A large-scale mutation search reveals genetic heterogeneity in 3M syndrome

The 3M syndrome is a rare autosomal recessive disorder recently ascribed to mutations in the CUL7 gene and characterized by severe pre- and postnatal growth retardation. Studying a series of 33 novel cases of 3M syndrome, we have identified deleterious CUL7 mutations in 23/33 patients, including 19 novel mutations and one paternal isodisomy of chromosome 6 encompassing a CUL7 mutation. Lack of mutations in 10/33 cases and exclusion of the CUL7 locus on chromosome 6p21.1 in six consanguineous families strongly support the genetic heterogeneity of the 3M syndrome.     

Further expanding the mutational spectrum and investigation of genotype–phenotype correlation in 3M syndrome

3M syndrome is characterized by severe pre‐ and postnatal growth retardation, typical facial features, and normal intelligence. Homozygous or compound heterozygous mutations in either CUL7, OBSL1, or CCDC8 have been identified in the etiology so far. Clinical and molecular features of 24 patients (23 patients and a fetus) from 19 unrelated families with a clinical diagnosis of 3M syndrome were evaluated and genotype–phenotype correlations were investigated with the use of DNA sequencing, chromosomal microarray, and whole exome sequencing accordingly. A genetic etiology could be established in 20 patients (n = 20/24, 83%). Eleven distinct CUL7 or OBSL1 mutations, among which eight was novel, were identified in 18 patients (n = 18/24, 75%). Ten patients had CUL7 (n = 10/18, 56%) while eight had OBSL1 (n = 8/18, 44%) mutations. Birth weight and height standard deviation scores at admission were significantly (p < 0.05) lower in patients with CUL7 mutation compared to that of patients with OBSL1 mutation. Two patients with a similar phenotype had a de novo 20p13p deletion involving BMP2. No genetic etiology could be established in four patients (n = 4/28, 17%). This study yet represents the largest cohort of 3M syndrome patients from a single center in Turkey. Microdeletions involving BMP2 may cause a phenotype similar to 3M syndrome with some distinctive features. Larger cohort of patients are required to establish genotype–phenotype correlations in 3M syndrome.     

OBSL1 mutations in 3‐M syndrome are associated with a modulation of IGFBP2 and IGFBP5 expression levels

3‐M syndrome is an autosomal recessive disorder characterized by severe pre‐ and postnatal growth retardation and minor skeletal changes. We have previously identified CUL7 as a disease‐causing gene but we have also provided evidence of genetic heterogeneity in the 3‐M syndrome. By homozygosity mapping in two inbred families, we found a second disease locus on chromosome 2q35–36.1 in a 5.2‐Mb interval that encompasses 60 genes. To select candidate genes, we performed microarray analysis of cultured skin fibroblast RNA from one patient, looking for genes with altered expression; we found decreased expression of IGFBP2 and increased expression of IGFBP5. However, direct sequencing of these two genes failed to detect any anomaly. We then considered other candidate genes by their function/location and found nine distinct mutations in the OBSL1 gene in 13 families including eight nonsense and one missense mutations. To further understand the links between OBSL1, CUL7, and insulin‐like growth factor binding proteins (IGFBPs), we performed real‐time quantitative PCR (RT‐PCR) analysis for OBSL1, CUL7, IGFBP2, and IGFBP5, using cultured fibroblast RNAs from two patients with distinct OBSL1 mutations (p.F697G; p.H814RfsX15). We found normal CUL7 mRNA levels but abnormal IGFBP2 and IGFBP5 mRNA levels in the two patients, suggesting that OBSL1 modulates the expression of IGFBP proteins. Hum Mutat 30:1–7, 2009. © 2009 Wiley‐Liss, Inc.     

A novel nonsense mutation in CUL4B gene in three brothers with X‐linked mental retardation syndrome

Badura‐Stronka M, Jamsheer A, Materna‐Kiryluk A, Sowińska A, Kiryluk K, Budny B, Latos‐Bieleńska A. A novel nonsense mutation in CUL4B gene in three brothers with X‐linked mental retardation syndrome. Cabezas syndrome (MIM 300354) is a recently identified syndromic form of X‐linked mental retardation (XLMR) caused by mutations in the CUL4B gene. In total, nine XLMR families carrying mutations in the CUL4B gene have been described to date. Here, we present a detailed clinical phenotype of three affected brothers of Polish descent. Based on the symptoms, we made a clinical diagnosis of Cabezas syndrome, which was subsequently confirmed by identification of a novel nonsense mutation (c.2107A→T, p.703K→X) in exon 18 of the CUL4B gene. The mutation was inherited from an asymptomatic mother and was present in all three affected brothers. The patients presented with typical features of Cabezas syndrome, such as severe mental retardation, speech impairment, hyperactivity, seizures, intention tremor, inguinal hernia, small feet, and craniofacial dysmorphism. In addition to previously described symptoms, syndactyly of the second and third toes and skin manifestations (hyperhydrosis and keratosis pilaris) were present in our cases. Our report provides further support that Cabezas syndrome is a recognizable syndromic form of XLMR. We conclude that the CUL4B gene should be screened in males with severe speech impairment and primary intention tremor, especially if characteristic facial dysmorphism is also present.     

Interstitial deletion in 3q in a patient with blepharophimosis-ptosis-epicanthus inversus syndrome (BPES) and microcephaly, mild mental retardation and growth delay: clinical report and review of the literature

We present a boy with blepharophimosis, ptosis, epicanthus inversus, microcephaly, mild mental retardation, and growth delay. Chromosomal analysis revealed a male karyotype with an interstitial deletion in the long arm of chromosome 3. DNA-analysis showed that the deletion is of maternal origin and encompasses the region between markers D3S1535 and D3S1593. The deletion contains not only the FOXL2 gene, but also the gene encoding ataxia-telangiectasia and Rad3-related protein (ATR). Mutations in FOXL2 have been shown to cause blepharophimosis-ptosis-epicanthus inversus syndrome (BPES). ATR has been identified as a candidate gene for Seckel syndrome, an autosomal recessive syndrome that comprises growth retardation, microcephaly, and mental retardation. We hypothesize that our patient has a contiguous gene syndrome and that the non-BPES-associated abnormalities (microcephaly, mild mental retardation, and growth delay) are the result of the deletion of the maternal ATR gene. However, it has not yet been excluded that haploinsufficiency of some other gene in this region plays a role.     

Is autosomal recessive Silver–Russel syndrome a separate entity or is it part of the 3‐M syndrome spectrum?

Intrauterine growth retardation (IUGR) is a nonspecific finding that occurs in approximately 0.17% of all live-births. However, IUGR can also be a significant feature of many recognized genetic syndromes including Silver-Russel syndrome (SRS), Three M syndrome (3-M), Dubowitz syndrome, and Mulibrey nanism. Differentiation of 3-M syndrome from autosomal recessive SRS has been difficult because of the phenotypic variability of the latter. Limb length asymmetry is seen in over half of those with autosomal recessive SRS, but not in individuals with 3-M syndrome. Characteristic radiologic findings of 3-M syndrome are not present in SRS. We used single nucleotide polymorphism (SNP) microarrays to investigate the cause of phenotypic features of SRS that shows autosomal recessive inheritance in three consanguineous families, two from United Arab Emirates (UAE), and one from Jordan. The mapped regions contained CUL7 and OBSL1, the genes that have recently been shown to cause 3-M syndrome. Subsequently, direct DNA sequencing of CUL7 and OBSL1 genes revealed novel mutations in both genes including two mutations in OBSL1 [c.1119G>C (p.W373C) and c.681_682delinsTT (p.Q228X)], and a nonsense mutation in CUL7 [c.203G>A (p.W68X)]. In addition, a six nucleotide deletion in CUL7 [c.649_654delAGCCGC (p.217_218delSR)] was found in a consanguineous family from UAE that had the typical features of 3-M. As a result of these findings, we question the identity of the autosomal recessive SRS and suggest that all apparently recessive SRS families should be tested for mutations in CUL7 and OBSL1.     

Maternal uniparental disomy of chromosome 4 in a patient with limb-girdle muscular dystrophy 2E confirmed by SNP array technology

The limb-girdle muscular dystrophies (LGMDs) are a heterogenous group of diseases characterized by shoulder-girdle and pelvic muscle weakness and wasting. LGMD 2E is an autosomal recessively inherited form of the disease caused by mutations in the β-sarcoglycan (SGCB) gene located at 4q12. In this report, we describe a patient who demonstrates non-Mendelian inheritance of a homozygous missense mutation in SGCB resulting in disease expression. A combination of single-nucleotide polymorphism (SNP) array technology and microsatellite analysis revealed the occurrence of maternal uniparental disomy (UPD) for chromosome 4 in the patient. As a consequence of segmental isodisomy at 4q12, the patient inherited two identical SGCB alleles carrying a missense mutation predicted to result in abnormal protein function. SNP array technology proved to be an elegant means to determine the most probable mechanism of UPD formation in this case, and enabled us to determine the location of recombination events along chromosome 4. In our patient, UPD likely arose from a trisomy rescue event due to maternal meiotic non-disjunction that we speculate may have been caused by abnormal recombination at the pericentromeric region. Maternal UPD 4 is a rare finding, and to our knowledge this is the first reported case of UPD in association with LGMD.     

Poland anomaly--report of an unusual family

Angelman syndrome (AS) is a neurodevelopmental disorder characterized by mental retardation, speech impairment, ataxia, and happy disposition with frequent smiling. AS results from the loss of expression of a maternal imprinted gene, UBE3A, mapped within 15q11-q13 region, due to different mechanisms: maternal deletion, paternal UPD, imprinting center mutation, and UBE3A mutation. Deletion AS patients may exhibit hypopigmentation of skin, eye, and hair correlating with deletion of P gene localized in the distal part of Prader-Willi (PWS)/AS region. Our patient presented developmental delay, severe mental retardation, absence of speech, outbursts of laughter, microcephaly, ataxia, hyperactivity, seizures, white skin, no retinal pigmentation, and gold yellow hair. His parents were of African ancestry. The SNURF-SNRPN methylation analysis confirmed AS diagnosis and microsatellite studies disclosed deletion with breakpoints in BP2 and BP3. All of the 25 exons and flanking introns of the P gene of the patient, his father, and mother were investigated. The patient is hemizygous for the deleted exon 7 of the P gene derived from his father who is a carrier of the deleted allele. Our patient manifests OCA2 associated with AS due to the loss of the maternal chromosome 15 with the normal P allele, and the paternal deletion in the P gene. As various degrees of hypopigmentation are associated with PWS and AS patients, the study of the P gene in a hemizygous state could contribute to the understanding of its effect on human pigmentation during development and to disclose the presence of modifier pigmentation gene(s) in the PWS/AS region.     

Characterization of a familial balanced rec(13) in a child with mild MR and his half-sibling with two structurally rearranged chromosomes 13

In this report, we describe a 7-year-old child with mild mental retardation, developmental delay, and learning disabilities. His karyotype contained a rearrangement of chromosome 13, which appeared to include a duplication of 13q31-qter and a deletion of 13p12-pter regions. The chromosomal origin of the additional material was confirmed by fluorescence in situ hybridization (FISH) using a whole chromosome painting probe specific for chromosome 13. Family studies showed that his mother carried a balanced inversion of chromosome 13 and that his half-brother carried the balanced pericentric inversion of chromosome 13 from his mother as well as another structural rearrangement involving chromosome 13 presumably from his father. The findings from this study suggested that the proband's abnormal 13 resulted from an unbalanced crossing-over between the normal and maternal inverted chromosome 13.     

First reported case of intrachromosomal cryptic inv dup del Xp in a boy with developmental retardation

We report here on a 6-year-old boy referred to the laboratory for karyotyping and SHOX microdeletion testing. The most significant clinical findings in this boy were small stature, Madelung deformity, facial dysmorphism, mild mental retardation and behavioral problems. R-, G- and RTBG-banding chromosome analysis showed a normal male karyotype. Fine molecular characterization, by FISH, of terminal Xp microdeletion revealed an associated partial duplication. Further refinement of the molecular analysis indicated an inverted duplication of the Xp22.31-Xp22.32 (13.7 Mb) region including the STS, VCX-A and KAL1 genes, associated with a terminal Xp deletion Xp22.33-Xpter (3.6 Mb) encompassing the SHOX and ARSE genes. Such rearrangements have been characterized for other chromosomal pairs, but this is the first reported male patient involving the short arm of the X chromosome. Molecular analysis of the maternal and patient's microsatellite markers showed interchromatid mispairing leading to non-allelic homologous recombination to be the most likely mechanism underlying this rearrangement. This case highlights the importance of clinically driven FISH investigations in order to uncover cryptic micro-rearrangements.     

Christianson syndrome in a patient with an interstitial Xq26.3 deletion

Interstitial deletions of chromosome band Xq26.3 are rare. We report on a 2-year-old boy in whom array comparative genomic hybridization analysis revealed an interstitial 314 kb deletion in Xq26.3 affecting SLC9A6 and FHL1. Mutations in SLC9A6 are associated with Christianson syndrome (OMIM 300243), a syndromic form of X-linked mental retardation (XLMR) characterized by microcephaly, severe global developmental delay, ataxia and seizures. FHL1 mutations cause Emery-Dreifuss muscular dystrophy (OMIM 310300), X-linked myopathy with postural muscle atrophy (XMPMA, OMIM 300696), scapuloperoneal myopathy (OMIM 300695), or reducing body myopathy (OMIM 300717, 300718). The clinical problems of the patient reported here comprised severe intellectual disability, absent speech, ataxia, epilepsy, and gastroesophageal reflux, and could mostly be attributed to SLC9A6 insufficiency. In contrast to the majority of reported Christianson syndrome patients who were microcephalic, this patient was normocephalic, but his head circumference had decelerated from the 50th centile at birth to the 25th centile at the age of 2 2/12 years. Muscle problems due to the FHL1 deletion are not to be expected before late childhood, which is the earliest age of onset for FHL1 associated Emery-Dreifuss muscular dystrophy. This patient broadens the spectrum of SLC9A6 mutations and contributes to the clinical delineation of Christianson syndrome. This is also the first patient with a deletion affecting both SLC9A6 and the complete FHL1 gene.     

Silver-Russell syndrome due to maternal uniparental disomy 7 and a familial reciprocal translocation t(7;13)

Behnecke A, Hinderhofer K, Jauch A, Janssen JWG, Moog U. Silver-Russell syndrome due to maternal uniparental disomy 7 and a familial reciprocal translocation t(7;13). Silver-Russell syndrome (SRS) is a genetically heterogeneous disorder characterized by intrauterine and postnatal growth retardation, typical facial features and a spectrum of additional features including body and limb asymmetry and clinodactyly. Maternal uniparental disomy for chromosome 7 (upd(7)mat) was shown to occur in 5-10% of patients with SRS. Maternal UPD7 is clinically often associated with mild SRS. Parents of an affected child are given a negligible recurrence risk as all reported cases with upd(7)mat have been sporadic so far. In general, chromosomal rearrangements-like translocations increase the likelihood of uniparental disomy (UPD) for the chromosomes involved. However, SRS as the result of a upd(7)mat in association with an inherited chromosomal translocation involving chromosome 7 has only been reported once before. Here, we describe the second case of SRS with upd(7)mat due to a familial reciprocal translocation t(7;13). This emphasizes the importance of chromosome analysis in SRS patients with upd(7)mat to rule out chromosomal rearrangements despite their rare occurrence as they are of great relevance for genetic counseling of SRS families.     

Transmission of ring chromosome 13 from a mother to daughter with both having a 46,XX, r(13)(p13q34) karyotype

Ring chromosomes are thought to be the result of breakage in both arms of a chromosome, with fusion of the points of fracture and loss of the distal fragments. Another mechanism of ring formation is believed to be the simple fusion of chromosome ends with preservation of telomeric and subtelomeric sequences. Ring chromosome 13 was first described in 1968 and its incidence estimated at 1 in 58,000 live births. Severe phenotypes associated with large deletions of 13q have been described as "ring chromosome 13 syndrome." Features of the "ring chromosome 13 syndrome" include mental retardation (often severe), growth retardation, microcephaly, facial dysmorphism, and hand, foot or toe abnormalities. We report on a case of a mother and daughter with r(13) and mild phenotypes. Our patient, IA, had chromosome analysis performed at about 4(1/2) years of age due to some developmental delay. This revealed 46,XX, r(13)(p13q34) karyotype with no loss of any chromosomal band. Her mother, EA, was subsequently found to have the same ring 13. IA's maternal grandmother had a normal karyotype while her maternal grandfather was unavailable for testing. Fluorescence in situ hybridization (FISH) analysis showed loss of a specific subtelomeric 13q region in r(13) in the mother. Clinically, IA had macular hyperpigmentation on the chin and mild delay in speech and fine motor skills. EA, 22 years of age, had mild short stature and borderline mental retardation. To our knowledge, this is the first report of a case of familial transmission of r(13). We compare phenotypes of our cases with those from other reported cases of r(13) and discuss the possible mechanism of formation of this ring chromosome.     

Autism, language delay and mental retardation in a patient with 7q11 duplication

Background

Chromosomal rearrangements, arising from unequal recombination between repeated sequences, are found in a subset of patients with autism. Duplications involving loci associated with behavioural disturbances constitute an especially good candidate mechanism. The Williams–Beuren critical region (WBCR), located at 7q11.23, is commonly deleted in Williams–Beuren microdeletion syndrome (WBS). However, only four patients with a duplication of the WBCR have been reported to date: one with severe language delay and the three others with variable developmental, psychomotor and language delay.

Objective and Methods

In this study, we screened 206 patients with autism spectrum disorders for the WBCR duplication by quantitative microsatellite analysis and multiple ligation‐dependent probe amplification.

Results

We identified one male patient with a de novo interstitial duplication of the entire WBCR of paternal origin. The patient had autistic disorder, severe language delay and mental retardation, with very mild dysmorphic features.

Conclusion

We report the first patient with autistic disorder and a WBCR duplication. This observation indicates that the 7q11.23 duplication could be involved in complex clinical phenotypes, ranging from developmental or language delay to mental retardation and autism, and extends the phenotype initially reported. These findings also support the existence of one or several genes in 7q11.23 sensitive to gene dosage and involved in the development of language and social interaction.     

Trisomy 7 mosaicism prenatally misdiagnosed and maternal uniparental disomy in a child with pigmentary mosaicism and Russell- Silver syndrome

Prenatal diagnosis of true mosaic trisomy 7 is rare in amniotic fluid and can be misinterpreted as pseudomosaic. The phenotype is highly variable and may be modified by a maternal uniparental disomy of chromosome 7 leading to mild Russell-Silver syndrome (RSS). We report here the third postnatal case of mosaic trisomy 7 with maternal uniparental disomy of chromosome 7 in a boy presenting a mild RSS. Fetal karyotype performed in amniocentesis for intrauterine growth retardation was considered normal. Mosaic trisomy 7 was diagnosed after birth, on fibroblasts karyotype performed for blaschkolinear pigmentary skin anomalies and failure to thrive. Maternal uniparental disomy of chromosome 7 was observed in blood sample. Retrospectively, trisomic 7 cells were identified in one prenatal long-term flask culture revealing a prenatal diagnosis failure. This report emphasizes the difficulty of assessing fetal mosaicism and distinguishing it from pseudomosaicism in cultured amniocytes. It is important to search for uniparental disomy as an indirect clue of trisomy 7 mosaicism and a major prognosis element. Although there are only few prenatal informative cases, detection of trisomy 7 in amniocentesis appears to be associated with a relatively good outcome when maternal uniparental disomy has been ruled out.     

An infant with deletion of the distal long arm of chromosome 15 (q26.1→qter) and loss of insulin-like growth factor 1 receptor gene

We report on an infant with a previously undescribed chromosome 15 deletion (q26.1→qter) and compare the clinical findings with those of 7 reported patients with deletions of distal 15q, as well as ring chromosome 15 syndrome patients. Most of the patients with deletions of distal 15q, including our patient, have intrauterine growth retardation (IUGR), microcephaly, abnormal face and ears, micrognathia, highly arched palate, renal abnormalities, lung hypoplasia, failure to thrive, and developmental delay/mental retardation. Several genes have been assigned to the 15q25→qter region, including insulin-like growth factor 1 receptor (IGF1R). DNA analysis from our patient documented the loss of one IGF1R gene copy. Our study further localizes the IGF1R gene distal to the 15q26.1 band. It is interesting to speculate that the severe IUGR and postnatal growth deficiency of our patient and other patients with similar chromosome 15 deletions are related to the loss of an IGF1R gene copy which may lead to an abnormal number and/or structure of the receptors.     

A 6Mb deletion in band 2q22 due to a complex chromosome rearrangement associated with severe psychomotor retardation, microcephaly and distinctive dysmorphic facial features

High-resolution analyses of complex chromosome rearrangements (CCR) have demonstrated in individuals with abnormal phenotypes that not all seemingly balanced CCRs based on G-banding are completely balanced at breakpoint level. Here we report on an apparently balanced de novo CCR involving chromosomes 2, 3 and 5 present in a 6-month-old girl. She was referred for genetic evaluation because of severe psychomotor retardation, distinctive dysmorphic features and microcephaly. A 1Mb resolution array-CGH analysis of DNA from the patient revealed a deletion of about 6Mb for chromosome 2. FISH analysis showed that the deletion interval found in band 2q22 mapped at the translocation breakpoint, and that the ZFHX1B gene, which is known to be involved in the Mowat-Wilson syndrome, is located within the deletion interval. To our knowledge this is the first case of a complex chromosomal rearrangement associated with Mowat-Wilson syndrome. Our data illustrate the important role for high-resolution investigation of apparently balanced chromosome rearrangements in patients with unexplained psychomotor retardation and/or other clinical features, and should contribute to our understanding of the mechanisms involved in chromosome rearrangement.     

Uniparental disomy 7 in Silver--Russell syndrome and primordial growth retardation

Maternal uniparental disomy for the entire chromosome 7 hasso far been reported in three patients with intrauterine andpostnatal growth retardation. Two were detected because theywere homozygous for a cystic fibrosis mutation for which onlythe mother was heterozygous, and one because he was homozygousfor a rare COL1A2 mutation. We investigated 35 patients witheither the Silver-Russell syndrome or primordial growth retardationand their parents with PCR markers to search for uniparentaldisomy 7. Four of 35 patients were found to have maternal disomy,including three with isodisomy and one with heterodisomy. Thedata confirm the hypothetical localization of a maternally imprintedgene (or more than one such gene) on chromosome 7. It is suggestedto search for UPD 7 in families with an offspring with sporadicSilver-Russell syndrome or primordial growth retardation.