top of page


collaboration and innovation

DSCAM, a conserved gene involved in neuronal differentiation, is a member of the Ig superfamily of cell adhesion molecules. Herein, we report the functional char- acterization of a human DSCAM (Down syndrome cell adhesion molecule) paralogue, DSCAML1, located on chromosome 11q23. The deduced DSCAML1 protein contains 10 Ig domains, six fibronectin-III domains, and an intracellular domain, all of which are structurally identical to DSCAM. When compared to DSCAM, DSCAML1 protein showed 64% identity to the extracellular domain and 45% identity to the cytoplasmic domain. In the mouse brain, DSCAML1 is predominantly expressed in Purkinje cells of the cerebellum, granule cells of the dentate gyrus, and in neurons of the cerebral cortex and olfactory bulb. Biochemical and immunofluorescence analyses indicated that DSCAML1 is a cell surface mol- ecule that targets axonal features in differentiated PC12 cells. DSCAML1 exhibits homophilic binding activity that does not require divalent cations. Based on its structural and functional properties and similarities to DSCAM, we suggest that DSCAML1 may be involved in formation and maintenance of neural networks. The chromosomal locus for DSCAML1 makes it an ideal can- didate for neuronal disorders (such as Gilles de la Tourette and Jacobsen syndromes) that have been mapped on 11q23.

Folate-sensitive fragile sites are associated with the expansion and hypermethylation of CCG-repeats. The fragile site in 11q23.3, FRA11B, has been shown to cause chromosome deletions in vivo, its expression being associated with Jacobsen (11q–) syndrome.However, the majority of Jacobsen deletions are distal toFRA11B and are not related to its expression. To test the hypothesis that other unidentified fragile sites might be located in 11q23.3–24 and may cause these deletions, we have identified and characterised CCG-trinucleotide repeats within a 40 Mb YAC contig spanning distal chro- mosome 11q. Only eight CCG-repeats were identified within the entire YAC contig (not including FRA11B), six of which map to the region of 11q23.3–24 that includes Jacobsen deletions. We have previously collated the deletion mapping data of 24 Jacobsen patients with the physical map of chromosome 11q, and accurately local- ised six breakpoints to short intervals corresponding to individual YAC clones. We now show that in each of these cases, YAC clones found to contain a deletion breakpoint also contain a CCG-repeat. The improved analysis of one of these deletions, together with those of several new Jacobsen cases, further strengthens this association by localising five breakpoints to individual PAC clones containing CCG-repeats. These data provide strong evidence for the non-random clustering of chromosome deletion breakpoints with CCG-repeats, and suggests that they may play an important role in a common mechanism of chromosome breakage.

A del(l1) (q24.2) was ascertained in a 2-year- old child and subsequently in her 20-year- old mother. Both mother and daughter had developmental delay, short stature, and “coarse”facial appearance.We compare our patients’manifestations to those associated with the distal llq2 deletion phenotype (“Jacobsen”syndrome),and to the one other reported case of del(W(q24.2).Our patients did not resemble this latter case, but had some findings in common with Jacobsen syndrome. We present our findings in order to contribute to the information on llq2 deletions.

The 11q terminal deletion disorder (11q-) is a rare chromosomal disorder caused by a deletion in distal 11q. Fifty-six percent of patients have clinically significant congenital heart defects. A cardiac ‘‘critical region’’ has been identified in distal 11q that contains over 40 annotated genes. In this study, we identify the distal breakpoint of a patient with a paracentric inversion in distal 11q who had hypoplastic left heart and congenital throm- bocytopenia. The distal breakpoint mapped to JAM-3, a gene previously identified as a candidate gene for causing HLHS in 11q-. To determine the role of JAM-3 in cardiac development, we performed a comprehensive cardiac phenotypic assessment in which the mouse homolog for JAM-3, JAM-C, has been deleted. These mice have normal cardiac structure and function, indicat- ing that haplo-insufficiency of JAM-3 is unlikely to cause the congenital heart defects that occur in 11q- patients. Notably, we identified a previously undescribed phenotype, jitteriness, in most of the sick or dying adult JAM-C knockout mice. These data provide further insights into the identification of the putative disease-causing cardiac gene(s) in distal 11q, as well as the functions of JAM-C in normal organ development.

Jacobsen syndrome is a rare disorder, caused by segmental monosomy for the distal end of the long arm of chromosome 11 with variable phenotypic expressivity. We report on the first male (6 years old) and female (3 years old) sibs with clinical and cytogenetics characterization of Jacobsen syndrome. Their karyotypes showed deletion 11q23.3-qter. Patients presented with growth and psychomotor retardation, facial dysmorphism, eye anomalies, and congenital heart disease (variable degrees of septal defect). Family history revealed a clinically similar brother, who died at 2 months old from cardiac anomalies in the form of single ventricle without being subjected to further investigations. Chromosomal analysis of the parents was normal. Karyotyping for the 2 patients and their parents was confirmed by fluorescence in situ hybridization analysis (FISH) using whole chromosome painting probes for 11 (WCP 11). Relevant investigations for both sibs showed mild thrombocytopenia with normal platelets morphology and striking periventricular demyelination on neuroimaging. Inguinal small testicles as well as focal epileptiform dysfunction were recorded in the male patient only. Abdominal ultrasound, hearing test, and DEXA scan were normal in both patients. Due to of the presence of apparently 3 affected offspring and normal parental karyotypes, an inherited predisposition was highly suspected. The large size of the distal deleted 11q segment in our patients support the recent hypothesis, that Jacobsen syndrome is a chromosomal deletion syndrome with genetic predisposition, due to expansion of p(CCG)n trinucleotide in the folate-sensitive fragile site FRA11B, at breakpoint 11q23.3. In conclusion, identification and further delineation of more similar patients will contribute to understanding the genetic basis of the 11q phenotype.

Jacobsen syndrome (JS), a rare disorder with multiple dysmorphic features, is caused by the terminal deletion of chromosome 11q. Short sta- ture has been reported in this syndrome, however very few of these patients have undergone endo- crine evaluation. Serum insulin-like growth fac- tor-1 (IGF-1) levels are an indirect indicator of growth hormone activity and are a useful initial screening tool in the assessment of an individual’s growth hormone axis. We studied nine children with JS, eight of whom had short stature. Four out of eight children with short stature (50%) had low IGF-1 values, with three low for age and one low for Tanner stage. Four out of six males (67%) had cryptorchidism, a potential sign of hypogonad- ism. We conclude that low IGF-1 is common in patients with JS and short stature, and that growth hormone status and possibly hypothala- mic-pituitary function should be evaluated in this patient population.

Paris-Trousseau syndrome (PTS; also known as Jacobsen syndrome) is characterized by several congenital anomalies including a dysmegakaryopoiesis with two morphologically distinct populations of megakaryocytes (MKs). PTS patients harbor deletions on the long arm of chromosome 11, including the FLI1 gene, which encodes a transcription factor essential for megakaryopoiesis. We show here that lentivirus-mediated overexpression of FLI1 in patient CD34+ cells restores the megakaryopoiesis in vitro, indicating that FLI1hemizygous deletion contributes to the PTS hematopoietic defects. FISH analysis on pre-mRNA and single-cell RT-PCR revealed that FLI1 expression is mainly monoallelic in CD41+CD42– progenitors, while it is predomi- nantly biallelic in the other stages of megakaryopoiesis. In PTS cells, the hemizygous deletion of FLI1 gener- ates a subpopulation of CD41+CD42– cells completely lacking FLI1 transcription. We propose that the absence of FLI1 expression in these CD41+CD42– cells might prevent their differentiation, which could explain the segregation of the PTS MKs into two subpopulations: one normal and one composed of small immature MKs undergoing a massive lysis, presumably originating from either FLI1+ or FLI1– CD41+CD42– cells, respectively. Thus, we point to the role of transient monoallelic expression of a gene essential for differentiation in the genesis of human haploinsufficiency-associated disease and suggest that such a mechanism may be involved in the pathogenesis of other congenital or acquired genetic diseases.

The ETS gene Fli-1 is involved in the induction of eryth- roleukemia in mice by Friend murine leukemia virus and Ewings sarcoma in children. Mice with a targeted null mutation in the Fli-1 locus die at day 11.5 of em- bryogenesis with loss of vascular integrity leading to bleeding within the vascular plexus of the cerebral meninges and specific downregulation of Tek/Tie-2, the receptor for angiopoietin-1. We also show that dysmegakaryopoiesis in Fli-1 null embryos resembles that frequently seen in patients with terminal deletions of 11q (Jacobsen or Paris-Trousseau Syndrome). We map the megakaryocytic defects in 14 Jacobsen pa- tients to a minimal region on 11q that includes the Fli-1gene and suggest that dysmegakaryopoiesis in these patients may be caused by hemizygous loss of Fli-1.

We report on two cases of distal monosomy 11q and partial trisomy 16q due to a familial subtle translocation detected by FISH subtelomere screening. Exact breakpoint analyses by FISH with panels of BAC probes demonstrated a 9.3 – 9.5 megabase partial monosomy of 11q24.2-qter and a 4.9–5.4 megabase partial trisomy of 16q24.1-qter. The index patient displayed craniofacial dysmorphisms, mild mental retardation and postnatal growth retardation, muscular hypotonia, mild periventricular leukodystrophy, patent ductus arteriosus, thrombocytopenia, recurrent infections, inguinal hernia, cryptorchidism, pes equinovarus, and hearing deficiencies. In his mother’s cousin who bears the identical unbalanced trans- location, mild mental retardation, patent ductus arteriosus, hypogammaglobulinemia, recurrent infections, unilateral kidney hypoplasia, pes equi- novarus, and hearing deficiencies were reported. Since only four descriptions of cryptic or subtle partial trisomies 16q have been published to date, our patients contribute greatly to the delineation of the phenotype of this genomic imbalance. In contrast to this, terminal deletions of the long arm of chromosome 11 cause a haploinsufficiency disorder (Jacobsen syndrome) in which karyo- type–phenotype correlations are already being established. Here, our findings contribute to the refinement of a phenotype map for several Jacob- sen syndrome features including abnormal brain imaging, renal malformations, thrombocytope- nia/pancytopenia, inguinal hernia, testicular ectopy, pes equinovarus, and hearing defi- ciency.

Here we report the association of giant platelets and an increase in platelet volume in a 19-month-old black female with de novo del 11q24-qter. The deletion, which was visi- ble on karyotype, was further confirmed and more precisely localized by fluorescence in situ hybridization studies (FISH) that sho- wed the deletion to lie distal to the MLL gene region (11q23). Clinically, the case pre- sented less severe symptoms than Jacobsen syndrome-the well known partial deletion of the distal end of chromosome 11. Platelet glycoproteins CD 41, CD 42a, C 42b, CD 61, and PAC-1 were also assayed and found to be normally expressed. To our knowledge, giant platelets are described for the first time in the relevant deleted region.

Fragile sites are heritable specific chromosome loci that exhibit an increased frequency of gaps, poor staining, constrictions or breaks when chromosomes are exposed to partial DNA replication inhibition. They constitute areas of chromatin that fail to compact during mitosis.
They are classified as rare or common depending on their frequency within the population and are further subdivided on the basis of their specific induction chemistry into different groups differentiated as folate sensitive or non-folate sensitive rare fragile sites, and as aphidicolin, bromodeoxyuridine (BrdU) or 5-azacytidine inducible common fragile sites. Most of the known inducers of fragility share in common their potentiality to inhibit the elongation of DNA replication, particularly at fragile site loci.
Seven folate sensitive (FRA10A, FRA11B, FRA12A, FRA16A, FRAXA, FRAXE and FRAXF) and two non-folate sensitive (FRA10B and FRA16B) fragile sites have been molecularly characterized. All have been found to represent expanded DNA repeat sequences resulting from a dynamic mutation involving the normally occurring polymorphic CCG/CGG trinucleotide repeats at the folate sensitive and AT-rich minisatellite repeats at the non-folate sensitive fragile sites. These expanded repeats were demonstrated, first, to have the potential, under certain conditions, to form stable secondary non-B DNA structures (intra-strand hairpins, slipped strand DNA or tetrahelical structures) and to present highly flexible repeat sequences, both conditions which are expected to affect the replication dynamics, and second, to decrease the efficiency of nucleosome assembly, resulting in decondensation defects seen as fragile sites. Thirteen aphidicolin inducible common fragile sites (FRA2G, FRA3B, FRA4F, FRA6E, FRA6F, FRA7E, FRA7G, FRA7H, FRA7I, FRA8C, FRA9E, FRA16D and FRAXB) have been characterized at a molecular level and found to represent relatively AT- rich DNA areas, but without any expanded repeat motifs. Analysis of structural characteristics of the DNA at some of these sites (FRA2G, FRA3B, FRA6F, FRA7E, FRA7G, FRA7H, FRA7I, FRA16D and FRAXB) showed that they contained more areas of high DNA torsional flexibility with more highly AT-dinucleotide-rich islands than neighbouring non-fragile regions. These islands were shown to have the potential to form secondary non-B DNA structures and to interfere with higher-order chromatin folding. Therefore, a common fragility mechanism, characterized by high flexibility and the potential to form secondary structures and interfere with nucleosome assembly, is shared by all the cloned classes of fragile sites.
From the clinical point of view, the folate sensitive rare fragile site FRAXA is the most important fragile site as it is associated with the fragile X syndrome, the most common form of familial mental retardation, affecting about 1/4000 males and 1/6000 females. Mental retardation in this syndrome is considered as resulting from the abolition of the FMR1 gene expression due to hypermethylation of the gene CpG islands adjacent to the expanded methylated trinucleotide repeat. FRAXE is associated with X-linked non-specific mental retardation, and FRA11B with Jacobsen syndrome. There is also some evidence that fragile sites, especially common fragile sites, are consistently involved in the in vivo chromosomal rearrangements related to cancer, whereas the possible implication of common fragile sites in neuropsychiatric and developmental disorders is still poorly documented.

We present a family with multiple cytogenetic abnormalities, identified through a girl with several dysmorphic features and cardiac problems, suspected for Jacobsen syndrome. Cytogenetic analysis showed a 46,XX,del(11)(qter) karyotype, which was confirmed by fluorescence in situ hybridization (FISH). Cyto- genetic investigation of the parents showed a chromosome aberration in both: the father had a t(11;12)(p13;q22) transloca- tion and the mother was carrier of an ins(4;11)(p14;q24q25). FISH analysis with an 11q-subtelomeric probe from the second- generation telomere clone set and BACs from 11q24-q25 sug- gested a complex maternal rearrangement. However, subsequent array analysis showed a single interstitial deletion in the proband, derived from the maternal insertion. The aberrant karyotypes in both parents implicated an increased risk of unbalanced fetal chromosome composition, thus high risk for a child with multiple congenital abnormalities. Therefore, dur- ing the next pregnancy, the couple opted for prenatal diagnosis by means of amniocentesis. An interphase FISH strategy for uncultured amniotic fluid cells predicted two possible un- balanced fetal chromosome constitutions. Karyotyping of cul- tured amniotic cells confirmed one of the predicted unbalanced cytogenetic options, demonstrating the value of a fast interphase strategy for parents who both are carriers of a chromosomal abnormality. In addition, we present an overview of patients with Jacobsen syndrome and an interstitial 11q deletion reported thus far in literature.

We describe a male infant with unusual facial appearance, relative pancytopenia, bilateral simian creases, and an accessory nipple. Cytogenetic analysis showed deletion of the long arm of chromosome 11 [46,XY,del(11)(pter→q23.2:)]. Bone-marrow study showed a myelodysplastic change of hemopoietic cells compatible with periph- eral blood findings. Pachygyria of the tem- poral and frontal lobes was demonstrated by magnetic resonance image (MRI) of the brain. We present our findings in order to contribute to the information on 11q23 deletion. Am. J. Med. Genet. 75:341–344, 1998.


Jacobsen syndrome is a MCA/MR contiguous gene syndrome caused by partial deletion of the long arm of chromosome 11. To date, over 200 cases have been reported. The prevalence has been estimated at 1/100,000 births, with a female/male ratio 2:1. The most common clinical features include pre- and postnatal physical growth retardation, psychomotor retardation, and characteristic facial dysmorphism (skull deformities, hypertelorism, ptosis, coloboma, downslanting palpebral fissures, epicanthal folds, broad nasal bridge, short nose, v-shaped mouth, small ears, low set posteriorly rotated ears). Abnormal platelet function, thrombocytopenia or pancytopenia are usually present at birth. Patients commonly have malformations of the heart, kidney, gastrointestinal tract, genitalia, central nervous system and skeleton. Ocular, hearing, immunological and hormonal problems may be also present. The deletion size ranges from ~7 to 20 Mb, with the proximal breakpoint within or telomeric to subband 11q23.3 and the deletion extending usually to the telomere. The deletion is de novo in 85% of reported cases, and in 15% of cases it results from an unbalanced segregation of a familial balanced translocation or from other chromosome rearrangements. In a minority of cases the breakpoint is at the FRA11B fragile site. Diagnosis is based on clinical findings (intellectual deficit, facial dysmorphic features and thrombocytopenia) and confirmed by cytogenetics analysis. Differential diagnoses include Turner and Noonan syndromes, and acquired thrombocytopenia due to sepsis. Prenatal diagnosis of 11q deletion is possible by amniocentesis or chorionic villus sampling and cytogenetic analysis. Management is multi-disciplinary and requires evaluation by general pediatrician, pediatric cardiologist, neurologist, ophthalmologist. Auditory tests, blood tests, endocrine and immunological assessment and follow-up should be offered to all patients. Cardiac malformations can be very severe and require heart surgery in the neonatal period. Newborns with Jacobsen syndrome may have difficulties in feeding and tube feeding may be necessary. Special attention should be devoted due to hematological problems. About 20% of children die during the first two years of life, most commonly related to complications from congenital heart disease, and less commonly from bleeding. For patients who survive the neonatal period and infancy, the life expectancy remains unknown.

Jacobsen syndrome is a haploinsufficiency disorder caused, most frequently by terminal deletion of part of the long arm of chromosome 11, with breakpoints in 11q23.3–11q24.2. Inheritance of an expanded p(CCG)ntrinucleotide repeat at the folate-sensitive fragile site FRA11B has been implicated in the generation of the chromosome breakpoint in several Jacobsen syndrome patients. The majority of such breakpoints, however, map distal to this fragile site and are not linked with its expression. To characterize these distal breakpoints and ultimately to further investigate the mechanisms of chromosome breakage, a 40-Mb YAC contig covering the distal long arm of chromosome 11 was assembled. The utility of the YAC contig was demonstrated in three ways: (1) by rapidly mapping the breakpoints from two new Jacobsen syndrome patients using FISH; (2) by demonstrating conversion to high resolution PAC contigs after direct screening of PAC library filters with a YAC clone containing a Jacobsen syndrome breakpoint; and (3) by placing 23 Jacobsen syndrome breakpoints on the physical map. This analysis has suggested the existence of at least two new Jacobsen syndrome breakpoint cluster regions in distal chromosome 11.

a-Tectorin is one of the major noncollagenous com- ponents of the mammalian tectorial membrane in the inner ear. We have mapped the gene encoding a-tect- orin to mouse chromosome 9 and human chromosome 11 in a known region of conserved synteny. Human YAC clones containing a-tectorin have been identified, demonstrating physical linkage to the anonymous marker D11S925. This places atectorin within the genetic interval that contains both the human nonsyndromic autosomal dominant deafness DFNA12 and the proximal limit of a subset of deletions within Jacobsen syndrome. Thus both DFNA12 and the hearing loss in some cases of Jacobsen syndrome may be due to haploinsufficiency for TECTA.

More than 70 patients with Jacobsen syndrome have been described [Penny et al., 1995; Pivnick et al., 1996; Ono et al., 1996]. The Jacobsen syndrome comprises mild to moderate psychomotor retardation, trigonocephaly, minor facial anomalies, cardiac defects, and thrombocytopenia. The syndrome is caused by distal deletions of chromosome arm 11q, including 11q24.1. Until now, no clear correlation between genotype and phenotype could be established. Recently, Michaelis et al. [1998] showed that in most cases in which the breakpoint was distal to marker D11S924, the deleted chromosome was paternal in origin. We describe a patient with Jacobsen syndrome, due to a de novo trans- location (6;11)(p21;q25).


The 11q terminal deletion disorder or Jacobsen syndrome is a contiguous gene disorder. It is characterized by psychomotor retardation, cardiac defects, blood dyscrasias (Paris- Trousseau syndrome) and craniofacial anomalies. We report on a female patient with an approximately 10 Mb interstitial deletion with many of the features of Jacobsen syndrome: A congenital heart defect, dysmorphic features, developmental delay, and Paris-Trousseau syndrome. The karyotype of the patient is 46,XX,del(11)(q24.1q24.3). The interstitial deletion was confirmed using FISH probes for distal 11q, and the breakpoints were characterized by microarray analysis. This is the first molecularly characterized interstitial deletion in a patient with the clinical features of Jacobsen syndrome. The deletion includes FLI-1, but not JAM-3, which will help to determine the critical genes involved in this syndrome.

Recent studies have identified a (CCG)n repeat in the 5􏰊 untranslated region of the CBL2 protooncogene (11q23.3) and have demonstrated that expansion of this repeat causes expression of the folate-sensitive fragile site FRA11B. It has also been demon- strated that FRA11B is the site of breakage in some cases of Jacobsen syndrome (JS) involving terminal deletions of chromosome 11q. We report on 2 patients with JS and a 46,XX,del(11)(q23.3) karyotype. In both cases, microsatellite and fluorescence in situ hybridization analyses indicated that the deletion breakpoint was approximately 1.5–3 Mb telomeric to FRA11B. There was no evidence of expansion of the CBL2 (CCG)nrepeat in the parents of either patient. The deleted chromosome was of paternal origin in both cases, although it was of maternal origin in the cases reported to be caused by FRA11B. These findings and those in previously reported patients suggest that the breakpoint for most 11q deletions in JS patients is telomeric to FRA11B, which raises the possibility that there may be other fragile sites in 11q23.3 in addition to FRA11B. These findings also support previous evidence that there may be a propensity for breakpoints to differ depending on the parental origin of the deleted chromosome.

A routine detailed ultrasound examination performed at 20 weeks’ gestation demonstrated the presence of nuchal thickening as an apparently isolated finding. The concentration of maternal α-fetoprote in was normal and the risk of Down’s syndrome was 1 in 6800. Amniocentesis was performed and chromosome analysis showed the karyo- type 46,XY, del(11)(q23) found in Jacobsen syndrome. Fetal autopsy performed following medical termination at 23 weeks confirmed the phenotype and internal abnormalties found in Jacobsen syndrome.

Purpose: To discuss the ophthalmic findings and their clinical significance in 10 new cases of Jacobsen syndrome (mental retardation, craniofacial anomalies, congenital heart defects, and blood dyscrasias) and to review the ophthalmic findings in all previously reported cases in the literature. Methods: Ten new cases of Jacobsen syndrome were collected and studied prospectively for detection of abnormal ophthalmologic examination findings. A total of 63 previously reported cases were identified from Medline and analyzed for ophthalmologic abnormalities. Results: The most common ophthalmologic findings in the new cases of Jacobsen syndrome included strabismus (90.0%), refractive error (90.0%), and ptosis (70.0%). Facial dysmorphism was also common and included hypertelorism, epicanthal folds, and down-slanting palpebral fissures. Uncommon ophthalmic findings included 5 patients with retinal vascular tortuosity, 1 with glaucoma, and 3 with amblyopia. In 63 cases reviewed, 36 reported ophthalmologic abnormalities. The most common findings included facial anomalies and ptosis. Only 5 of the 63 patients had evidence of strabismus, and none were reported to have retinal vascular tortuosity. Conclusions: To prevent unnecessary vision loss in children with Jacobsen syndrome, proper screening for amblyogenic factors is imperative. We recommend a baseline complete ophthalmologic examination with subsequent follow-up examinations depending on the particular findings noted during the initial screening visit.

The thrombocytopenia in an infant with clinical features of Jacobsen’s syndrome char- acterized by multiple congenital anomalies, cardiac defects, psychomotor retardation, and deletion of chromosome 11 at 11q23.3 has been evaluated. Study of his platelets in the electron microscope revealed giant alpha granules in his cells identical in appearance to those reported in the family with Paris-Trousseau syndrome. As a result, the Paris- Trousseau syndrome appears to be a variant of the Jacobsen syndrome, and the throm- bocytopenia observed in all cases of chromosome 11q23.3 deletion due to dysmega- karyopoieses. Giant alpha granules are frequently observed in normal platelets during long-term storage and may form in Jacobsen and Paris-Trousseau platelets during pro- longed residence in the bone marrow.

Two cases, a boy and a girl, with the 11q-(Jacobsen) syndrome are reported. Findings common to both and typical for this chromosome aberration include a narrow protruding forehead, hypertelorism, non-horizontal position of the eyes, ptosis, strabismus, broad root, and short upturned tip of thenose, carp mouth, receding chin, misshapen ears, simian creases, and severe mental retardation. In addition, one patient had pyloric stenosis and an inguinal hernia. Growth retardation and microcephaly were not found in either of them. The karyotypes revealed de novo-deletions of the long arm of one chromosome 11,del(11)(q23).


The clinical features of partial deletion 11q were correlated with the size of the deleted region. Ten Japanese children with partial deletion of 11q were investigated. They were divided into three groups. Three patients in the first group had interstitial deletions and preserved subband q24.1. Six patients in the second group demonstrated terminal deletion of 11q including subband q24.1, with typical features of 11q- syndrome (Jacobsen syndrome). The third group included only one patient, who had terminal deletion of 11q without characteristics of typical 11q- syndrome. Prominent features of patients in the first group included severe mental and motor developmental delay, seizures, cleft lip and palate, and ophthalmological findings. Patients in the second group showed mild to moderate developmental delays without deterioration. Abnormalities in neuroimages, high intensity in the cerebral white matter in T2-weighted magnetic resonance (MR) images, and recurrent infections were not observed after the age of 7 years. The subject in the third group, with the smallest amount of deleted chromosome, did not show developmental delays, suggesting that some unknown genes related to developmental delays may be located adjacent to subband q24.1. Variation in the deleted parts of 11q resulted in different clinical features in each group.

Autosomal fragile sites, unlike their X-llnked counterparts, are not known to be associated with disease. However, one case report has highlighted a possible relationship between the Inheritance of a rare folate-sensitive fragile site in band 11q23.3 (FRA11B) and the chromosome 11q23-qter deletion in Jacobsen (11q-) syndrome. The mother and brother of the reported Jacobsen syndrome child are FRA11B carriers, suggesting that In vivo breakage at the fragile site during early development could have given rise to the chromosome deletion. We have tested this hypothesis by high resolution physical mapping of FRA11B and of the deletion chromosome breakpoint in the Jacobsen syndrome patient. A detailed restriction map of 600 kb of human chromosome band 11q23.3 has been assembled which covers the PBGD, CBL2 and THY1 genes. FISH experiments with YACs and cosmlds from this region have localised FRA 11B to an interval of approximately 100 kb containing the 5' end of the CBL2 gene, which includes a CCG trinucieotide repeat. This class of repeat is expanded In the four cloned examples of fragile site and therefore the CBL2 repeat is a candidate for the location of FRA11B. Further, it is shown that the chromosomal deletion breakpoint of the Jacobsen syndrome child maps within the same interval as the fragile site. The breakpoint has apparently been repaired and stabilised by the de novo addition of a telomere. These data are consistent with a role for an inherited fragile site in the aetiology of a chromosome deletion syndrome.

Jacobsen syndrome and Paris-Trousseau Syndrome share similar congenital anomalies, thrombocytopenia, giant platelet alpha granules resulting from fusion of smaller organelles, and an 11q terminal deletion at 11q23.3. Similarities in the two cohorts have suggested that the Paris-Trousseau Syndrome is a variant of Jacobsen syndrome, or the same disorder. The present study has pointed out a significant difference between the two syndromes. Platelets from six patients with Jacobsen syndrome were markedly diminished in serotonin adenine nucleotide rich dense bodies, indicating the presence of platelet storage pool deficiency. Since platelet dense bodies are reported to be normal in size, number and distribution in the Paris-Trousseau Syndrome, the presence of platelet storage pool deficiency in six patients evaluated in the present study may distinguish the two disorders.

We report a 10-years-old female patient with a partial trisomy 18q and monosomy 11q due to a maternal translocation. The phenotype of our proband is partially common with Jacobsen syndrome and duplication 18q but she has also some atypical anomalies such as precocious puberty, a retinal albinism and hypermetropia. Based on cytogenetics and FISH analysis, the karyotype of the proband was 46,XX,der(11)t(11;18)(q24;q13). To the best of our knowledge, this is the first report of precocious puberty associated with either dup(18q) or del(11q) syndromes

Objective To describe the prenatal phenotype of the 11q deletion syndrome (Jacobsen syndrome) and present the molecular characterization of the deletion in the case presented.
Case Ultrasound at 18 and 20 weeks of gestation, on a 34-year-old woman who presented for amniocentesis, revealed slow movements, oligohydramnios and dilatation of the cerebral ventricles in the fetus. Maternal and paternal ages were 34 and 38 years, respectively.
Results Prenatal karyotyping of cultured amniotic fluid cells revealed an 11q terminal deletion, 46,XX,del(11)(q23) (Jacobsen syndrome). Real-time quantitative PCR analysis was used to identify and map the breakpoint physically to a 45-kb region located 14.5 Mb from the 11q telomere. Polymorphic DNA marker analysis showed that DNA sequences on the paternally derived chromosome are deleted.
At autopsy, facial dysmorphism without major malformations was recorded. Examination of the internal organs disclosed the following abnormalities: a Meckels’ diverticulum of 4-mm length, adhesion between the gall bladder and the transverse colon, and bilaterally bilobed lungs without further situs anomalies.
Conclusion Our case demonstrates significant phenotypic variability of Jacobsen syndrome at midtrimester pregnancy; the syndrome may be manifested at this stage only by mild to moderate ventriculomegaly of the brain. Copyright  2006 John Wiley & Sons, Ltd.

The phenotype of 11q terminal deletion also known as Jacobsen syndrome is a clinically well known entity whose diagnosis in infancy and childhood is based on clinical examination, hematological and cytogenetic findings. Hematological features in Jacobsen syndrome are very similar to those reported in PariseTrousseau syndrome (PTS) which is also associated with11q terminal deletion. Karyotype analysis shows a variable terminal deletion from 11q23 sub-band extending to the telomere. Most often in patients with Jacobsen syndrome, this chromosomal deletion is present in all metaphases. We report on the identification of a distal 11q deletion in mosaic (20% of deleted cells) in a fetus ascertained after amnio- centesis for maternal serum screening test indicative for Down syndrome. The present case is the third prenatal diagnosis of a mosaic for a distal 11q deletion with the lowest mosaicism rate. The 2D-ultrasound examination and cord blood hematological studies were useful to estimate the prognosis at term, considering the contribution of the mosaicism rate to the phenotypic variability in Jacobsen syndrome. The identification of mosaicism for distal 11q deletion is a very rare event in prenatal diagnosis. This case illustrates the complexity in genetic counselling for prenatally ascertained partial monosomy 11qter in mosaic.

We describe a 34-year-old male patient with Jacobsen syndrome associated with a broad spectrum of anomalies and an increased susceptibility to infections. Features commonly seen in Jacobsen syndrome were short stature, mental retardation, congenital heart disease, cryptorchidism, strabismus, distal hypospadia glandis, and mild thrombocytopenia. Chromosome anal- ysis disclosed a mosaic 46,XY,del(11)(q24.1)/ 46,XY karyotype with a very low percentage of normal cells. In addition, transverse upper limb defect, imperforate anus, and hearing impairment were noted. Cellular anomalies include functional impairment and deficiency of T-helper cells, and a low serum immunoglobulin M (IgM)-level. The presence of a transverse limb defect and primary immunodeficiency has not been reported previously in Jacobsen syndrome.

Characteristics of sleep and sleep problems were investigated in 43 individuals with 11q terminal deletion disorder (Jacobsen syndrome). Data were collected using a sleep questionnaire. Ten individuals (23%) had a sleep problem. Settling problems, frequent night waking and early waking occurred in 2 (4%), 7 (16%) and 2 (6%) individuals, respectively. Twenty-two individuals (54%) had a history of sleep problems. Twenty-five individuals (60%) showed restless sleep and 23 individuals (54%) slept in an unusual position. Apart from frequent coughs, no significant relationships were found between the presence of a sleep problem and other variables, such as age, level of ID, breathing problems, heart defects, constipation, daytime activity and behavioral diagnosis, restless sleep and sleeping in an unusual positions.

Background: Jacobsen syndrome is a rare contiguous gene disorder that results from a terminal deletion of the long arm of chromosome 11. It is typically characterized by intellectual disability, a variety of physical anomalies and a distinctive facial appearance. The 11q deletion has traditionally been identified by routine chromosome analysis. Array-based comparative genomic hybridization (array-CGH) has offered new opportunities to identify and refine chromosomal abnormalities in regions known to be associated with clinical syndromes.

Results: Using the 1 Mb BAC array (Spectral Genomics), we screened 70 chromosomally normal children with idiopathic intellectual disability (ID) and congenital abnormalities, and identified five cases with submicroscopic abnormalities believed to contribute to their phenotypes. Here, we provide detailed molecular cytogenetic descriptions and clinical presentation of two unrelated subjects with de novo submicroscopic deletions within chromosome bands 11q24-25. In subject 1 the chromosome rearrangement consisted of a 6.18 Mb deletion (from 128.25–134.43 Mb) and an adjacent 5.04 Mb duplication (from 123.15–128.19 Mb), while in subject 2, a 4.74 Mb interstitial deletion was found (from 124.29–129.03 Mb). Higher resolution array analysis (385 K Nimblegen) was used to refine all breakpoints. Deletions of the 11q24-25 region are known to be associated with Jacobsen syndrome (JBS: OMIM 147791). However, neither of the subjects had the typical features of JBS (trigonocephaly, platelet disorder, heart abnormalities). Both subjects had ID, dysmorphic features and additional phenotypic abnormalities: subject 1 had a kidney abnormality, bilateral preauricular pits, pectus excavatum, mild to moderate conductive hearing loss and behavioral concerns; subject 2 had macrocephaly, an abnormal MRI with delayed myelination, fifth finger shortening and squaring of all fingertips, and sensorineural hearing loss.

Conclusion: Two individuals with ID who did not have the typical clinical features of Jacobsen syndrome were found to have deletions within the JBS region at 11q24-25. Their rearrangements facilitate the refinement of the JBS critical region and suggest that a) deletion of at least 3 of the 4 platelet function critical genes (ETS-1, FLI-1 and NFRKB and JAM3) is necessary for thrombocytopenia; b) one of the critical regions for heart abnormalities (conotruncal heart defects) may lie within 129.03 – 130.6 Mb; c) deletions of KCNJ1 and ADAMTS15 may contribute to the renal anomalies in Jacobsen Syndrome; d) the critical region for MRI abnormalities involves a region from 124.6 – 129.03 Mb. Our results reiterate the benefits of array-CGH for description of new phenotype/genotype associations and refinement of previously established ones.


We report on 3 kindred patients with terminal 11q monosomy and distal 22q trisomy involving theSHANK3 gene, resulting from a subtle familial translocation t(11;22)(q24.2;q13.33). The patients presented with the characteristic symptoms of Jacobsen syndrome (JBS), including: mental retardation, short stature, and craniofacial dysmorphism in all 3 cases; cardiac defects in 2 cases; and thrombocytopenia, brain abnormality, eye coloboma, recurrent infections, cryptorchidism and toe anomalies in single cases. The oldest patient also had Hashimoto disease and diabetes mellitus type 2. So far, these 2 conditions have not been reported in adult patients with JBS. Features typical for distal 22q trisomy in our patients include muscular hypotonia and prenatal failure to thrive, seen in 2 and 1 cases, respectively. We also present a family member with 11q24.2-qter trisomy and 22q13.33-qter monosomy, whose clinical phenotype is partially overlapping with several dysmorphic features of JBS. In addition, multiple pregnancy losses and infantile deaths occurred in this family, suggesting that these chromosomal imbalances may produce a lethal phenotype. FISH with a panel of BAC probes determined the ac- curate sizes of the deletion 11q (9.9 Mb) and trisomy 22q (0.8 Mb). To date, only 5 cases of submicroscopic 22q13.3-qter trisomy have been reported. A detailed clinical description of our patients, along with a precise cytogenetic designation of chromosomal breakpoints, allow further refinement of genotype-phenotype correla- tion for distal imbalances in 11q and 22q.

An apparently new syndrome of congenital cataracts, sensorineural deafness, Down syndrome-like facial appearance, short stature, and mental retardation was described by Gripp et al. [1996]. The authors reported on two unrelated patients with congenital cataracts, sensorineural deafness, distinctive facial appearance, mental retardation, postnatal short stature, and skeletal changes. We report on two additional patients with findings most similar to the reported patients by Gripp et al. [1996], including bilateral congenital cataracts, hearing loss, craniofacial abnormalities, short stature, skeletal abnormalities, and developmental delay. Both of the patients reported herein had chromosome microarray analysis, which showed normal results in Patient 2 but abnormal results in Patient 1 and his mother who both had a chromosome 11q25 subtelomere deletion. Patient 1 and his mother’s findings are atypical for the common
findings reported in Jacobsen syndrome (11q terminal deletion syndrome), and consistent with the patients reported by Gripp et al. [1996]. The etiology for these cases has been unknown. The microarray results on Patient 1 suggest that the other patients with findings of developmental delay, short stature, congenital cataracts, sensorineural hearing loss, and similar craniofacial features may have either a microdeletion of chromosome 11q terminal region or haploinsufficiency of a gene localized to this region.

We performed a prospective study of 110 patients (75 not previously published) with the 11q term- inal deletion disorder (previously called Jacobsen syndrome), diagnosed by karyotype. All the patients have multiple dysmorphic features. Nearly all the patients (94%) have Paris-Trous- seau syndrome characterized by thrombocytope- nia and platelet dysfunction. In total, 56% of the patients have serious congenital heart defects. Cognitive function ranged from normal intelli- gence to moderate mental retardation. Nearly half of the patients have mild mental retardation with a characteristic neuropsychiatric profile demon- strating near normal receptive language ability, but mild to moderate impairment in expressive language. Ophthalmologic, gastrointestinal, and genitourinary problems were common, as were gross and fine motor delays. Infections of the upper respiratory system were common, but no life-threatening infections were reported. We include a molecular analysis of the deletion breakpoints in 65 patients, from which genetic ‘‘critical regions’’ for 14 clinical phenotypes are defined, as well as for the neuropsychiatric profiles. Based on these findings, we provide a comprehensive set of recommendations for the clinical management of patients with the 11q terminal deletion disorder.

Fragile X syndrome is now a well established common clinical entity and most of those who are aware of the condition probably know that it takes its name from a rare fragile site (FRAXA) on the X chromo- some. This is the best known fragile site and its clinical significance is clear. Similar, but a little less known is FRAXE, a fragile site close to that associated with fragile X syndrome, but in this case associated with a mild form of non-specific X-linked mental retardation. These are the only two fragile sites that are unequivocally of clinical significance. A fragile site within the CBL2 oncogene on chromosome 11 has been mapped very close to the deletion breakpoint in a handful of patients with Jacobsen syndrome. It is doubtful that parents with FRA11B are at increased risk of having children with Jacobsen syndrome, but this cannot be ruled out.
The common fragile sites have been implicated in oncogenesis since shortly after their discovery in the early 1980s. While a couple of these are within genes that have been implicated in cancer it is unclear whether either the fragile sites, or the genes in which they are located are important in cancer. It may be that the common fragile sites are regions of genomic instability and that this instability is increased in malignant cells, analogous to the enhanced instability seen at mi- crosatellite loci in a number of tumours. Since we all have the common fragile sites there is no suggestion that they give anyone an increased risk of developing malignant disease.
In dealing with patients who are found to have fragile sites, other than FRAXA, FRAXE and possibly FRA11B, considerable reassurance can be given that they are not at increased risk of having children with congenital disease or developing disease themselves because of their fragile sites.

We report ophthalmic manifestations in four Jacobsen syndrome cases, review the liter- ature, and suggest phenotype-genotype correlations. Methods: Chart review of Ocular Genetics Program patients at The Hospital for Sick Children, Toronto, Canada. Results: Four del11qter cases are presented. Hypertelorism/telecanthus, abnormally slanted palpebral fissures, abnor- mal retinal findings, nasolacrimal duct obstruction, anomalous extraocular muscles, amblyopia, and microcornea were found. Conclusions: We report typical findings and novel ocular presen- tations. Visual prognosis is generally good. Retinal dysplasia and coloboma seem associated with del11q23. ABCG4, NCAM, and Mfrp are candidate genes in this region that theoretically may be disrupted.

Loss of PTEN causes unregulated activation of downstream components of phosphatidylinositol 3-kinase (PI3K) signaling, including PDK1, and disrupts normal nervous system development and homeostasis. We tested the contribution of Pdk1 to the abnormalities induced by Pten deletion in the brain. Conditional deletion ofPdk1 caused microcephaly. Combined deletion of Pdk1and Pten rescued hypertrophy, but not migration defects of Pten-deficient neurons. Pdk1 inactivation induced strik- ingly different effects on the regulation of phosphorylated Akt in glia versus neurons. Our results show Pdk1- dependent and Pdk1-independent abnormalities in Pten- deficient brains, and demonstrate cell type specific dif- ferences in feedback regulation of the ubiquitous PI3K pathway.

bottom of page