S.W. Cheung

22q13.3 Deletion Syndrome: Clinical and Molecular Analysis Using Array CGH

The 22q13.3 deletion syndrome results from loss of terminal segments of varying sizes at 22qter. Few genotype–phenotype correlations have been found but all patients have mental retardation and severe delay, or absence of, expressive speech. We carried out clinical and molecular characterization of 13 patients. Developmental delay and speech abnormalities were common to all and comparable in frequency and severity to previously reported cases. Array‐based comparative genomic hybridization showed the deletions to vary from 95u2009kb to 8.5u2009Mb. We also carried out high‐resolution 244K array comparative genomic hybridization in 10 of 13 patients, that defined the proximal and distal breakpoints of each deletion and helped determine the size, extent, and gene content within the deletion. Two patients had a smaller 95u2009kb terminal deletion with breakpoints within the SHANK3 gene while three other patients had a similar 5.5u2009Mb deletion implying the recurrent nature of these deletions. The two largest deletions were found in patients with ring chromosome 22. No correlation could be made with deletion size and phenotype although complete/partial SHANK3 was deleted in all patients. There are very few reports on array comparative genomic hybridization analysis on patients with the 22q13.3 deletion syndrome, and we aim to accurately characterize these patients both clinically and at the molecular level, to pave the way for further genotype–phenotype correlations.

Microdeletions including YWHAE in the Miller-Dieker syndrome region on chromosome 17p13.3 result in facial dysmorphisms, growth restriction, and cognitive impairment

Background: Deletions in the 17p13.3 region are associated with abnormal neuronal migration. Point mutations or deletion copy number variants of the PAFAH1B1 gene in this genomic region cause lissencephaly, whereas extended deletions involving both PAFAH1B1 and YWHAE result in Miller–Dieker syndrome characterised by facial dysmorphisms and a more severe grade of lissencephaly. The phenotypic consequences of YWHAE deletion without deletion of PAFAH1B1 have not been studied systematically. Methods: We performed a detailed clinical and molecular characterization of five patients with deletions involving YWHAE but not PAFAH1B1, two with deletion including PAFAH1B1 but not YWHAE, and one with deletion of YWHAE and mosaic for deletion of PAFAH1B1. Results: Three deletions were terminal whereas five were interstitial. Patients with deletions including YWHAE but not PAFAH1B1 presented with significant growth restriction, cognitive impairment, shared craniofacial features, and variable structural abnormalities of the brain. Growth restriction was not observed in one patient with deletion of YWHAE and TUSC5, implying that other genes in the region may have a role in regulation of growth with CRK being the most likely candidate. Using array based comparative genomic hybridisation and long range polymerase chain reaction, we have delineated the breakpoints of these nonrecurrent deletions and show that the interstitial genomic rearrangements are likely generated by diverse mechanisms, including the recently described Fork Stalling and Template Switching (FoSTeS)/Microhomology Mediated Break Induced Replication (MMBIR). Conclusions: Microdeletions of chromosome 17p13.3 involving YWHAE present with growth restriction, craniofacial dysmorphisms, structural abnormalities of brain and cognitive impairment. The interstitial deletions are mediated by diverse molecular mechanisms.

Deletion of 7q31.1 supports involvement of FOXP2 in language impairment : Clinical report and review

We report on a young male with moderate mental retardation, dysmorphic features, and language delay who is deleted for 7q31.1‐7q31.31. His full karyotype is 46,XY,der(7)del(7)(q31.1q31.31)ins(10;7)(q24.3;q31.1q31.31)mat. This child had language impairment, including developmental verbal dyspraxia, but did not meet criteria for autism according to standardized ADOS testing. Our patients deletion, which is the smallest reported deletion including FOXP2, adds to the body of evidence that supports the role of FOXP2 in speech and language impairment, but not in autism. A reported association between autism and deletions of WNT2, a gene also deleted in our patient, is likewise not supported by our case. Previously, fine mapping with microsatellites markers within in a large three‐generation family, in which half the members had severe specific language impairment, aided the localization of the SPCH1 locus to 7q31 within markers D7S2459 (107.1 Mb) and D7S643 (120.5 Mb). Additionally, chromosome rearrangement of 7q31 and mutational analyses have supported the growing evidence that FOXP2, a gene within the SPCH1 region, is involved with speech and language development. It is unclear however whether the AUTS1 (autistic spectrum 1) locus, highly linked to 7q31, overlaps with the SPCH1 and FOXP2.

TBX6 Null Variants and a Common Hypomorphic Allele in Congenital Scoliosis

BACKGROUNDnCongenital scoliosis is a common type of vertebral malformation. Genetic susceptibility has been implicated in congenital scoliosis.nnnMETHODSnWe evaluated 161 Han Chinese persons with sporadic congenital scoliosis, 166 Han Chinese controls, and 2 pedigrees, family members of which had a 16p11.2 deletion, using comparative genomic hybridization, quantitative polymerase-chain-reaction analysis, and DNA sequencing. We carried out tests of replication using an additional series of 76 Han Chinese persons with congenital scoliosis and a multicenter series of 42 persons with 16p11.2 deletions.nnnRESULTSnWe identified a total of 17 heterozygous TBX6 null mutations in the 161 persons with sporadic congenital scoliosis (11%); we did not observe any null mutations in TBX6 in 166 controls (P<3.8×10(-6)). These null alleles include copy-number variants (12 instances of a 16p11.2 deletion affecting TBX6) and single-nucleotide variants (1 nonsense and 4 frame-shift mutations). However, the discordant intrafamilial phenotypes of 16p11.2 deletion carriers suggest that heterozygous TBX6 null mutation is insufficient to cause congenital scoliosis. We went on to identify a common TBX6 haplotype as the second risk allele in all 17 carriers of TBX6 null mutations (P<1.1×10(-6)). Replication studies involving additional persons with congenital scoliosis who carried a deletion affecting TBX6 confirmed this compound inheritance model. In vitro functional assays suggested that the risk haplotype is a hypomorphic allele. Hemivertebrae are characteristic of TBX6-associated congenital scoliosis.nnnCONCLUSIONSnCompound inheritance of a rare null mutation and a hypomorphic allele of TBX6 accounted for up to 11% of congenital scoliosis cases in the series that we analyzed. (Funded by the National Basic Research Program of China and others.).

Deletion 9q34.3 syndrome: genotype-phenotype correlations and an extended deletion in a patient with features of Opitz C trigonocephaly

Submicroscopic deletion del(9)(q34.3) is a rare constitutional microdeletion syndrome involving the gene-rich subtelomeric region of the long arm of chromosome 9, with about 30 cases reported.1,2,3,4,5,6,7,8,9,10,11,12 Visible constitutional 9q34 deletions are extremely rare, with only a few cases described.2,10,12 The low prevalence of large terminal deletions at the 9q34 chromosome region in liveborns is thought to reflect lethality in early embryogenesis.13nnAt least 18 patients with 9q34.3 microdeletions detected by fluorescence in situ hybridisation (FISH) testing, in whom normal karyotypes were initially obtained, have been reported.1,5–7,11 Many patients carry a cryptic del(9)(q34.3) that may result in a clinically recognisable phenotype characterised by severe developmental delay, mental retardation, hypotonia, congenital heart defects (CHD), seizures, and prominent craniofacial features including microcephaly, arched eyebrows, hypertelorism, short nose with anteverted nostrils, open mouth, and a protruding tongue.6,7,11 Recently, based on clinical and molecular breakpoint analyses using FISH, microsatellites, and single nucleotide polymorphism (SNP) genotyping, two research groups have independently identified an ∼1.0 Mb shortest region of overlap (SRO) of 9q34.3 deletions.6,11 Although the clinical criteria and incidence of the 9q34.3 deletion are not yet well established, the increasing number of patients reported with del(9)(q34.3) is probably related to the widespread clinical application of telomere FISH. Hence, this microdeletion syndrome may be more common than previously thought.nnWe have identified a 9q34.3 deletion in each of five unrelated patients, including a patient with clinical features similar to Opitz trigonocephaly C syndrome (OTCS; MIMu200a211750). A monogenic cause and autosomal recessive mode of inheritance have been considered probable in OTCS, usually associated with a normal karyotype.14–19 In contrast, several reports on patients with multiple congenital anomalies resembling OTCS and chromosomal …

Different-Sized Duplications of Xq28, Including MECP2, in Three Males With Mental Retardation, Absent or Delayed Speech, and Recurrent Infections

In XY males, duplication of any part of the X chromosome except the pseudoautosomal region leads to functional disomy of the corresponding genes. We describe three unrelated male patients with mental retardation (MR), absent or delayed speech, and recurrent infections. Using high‐resolution comparative genomic hybridization (HR‐CGH), whole genome array comparative genomic hybridization (array CGH), fluorescent in situ hybridization (FISH), and multiplex ligation probe amplification (MLPA), we have identified and characterized two different unbalanced Xq27.3‐qter translocations on the Y chromosome (approx. 9 and 12 Mb in size) and one submicroscopic interstitial duplication (approx. 0.3–1.3 Mb) involving the MECP2 gene. Despite the differences in size of the duplicated segments, the patients share a clinical phenotype that overlaps with the features described in patients with MECP2 duplication. Our data confirm previous observations that MECP2 is the most important dosage‐sensitive gene responsible for neurologic development in patients with duplications on the distal part of chromosome Xq.

Congenital diaphragmatic hernia in WAGR syndrome

Wilms tumor, aniridia, genitourinary anomalies, and mental retardation (WAGR) syndrome is a contiguous gene deletion syndrome involving the Wilms tumor 1 gene (WT1), the paired box gene 6 (PAX6), and possibly other genes on chromosome 11p13. WT1 is required for normal formation of the genitourinary system and the high incidence of Wilms tumor and genitourinary anomalies found in patients with WAGR are attributed to haploinsufficiency of this gene. It has been hypothesized that WT1 also plays an important role in the development of the diaphragm. During mammalian embryonic development, WT1 is expressed in the pleural and abdominal mesothelium that forms part of the diaphragm. Furthermore, mice that are homozygous for a deletion in the mouse homolog of WT1 have diaphragmatic hernias. Case reports describing congenital diaphragmatic hernias in infants with Denys–Drash and Frasier syndromes, both of which can be caused by mutations in WT1, provide additional support for this hypothesis. We report an infant with aniridia, bilateral cryptorchidism, vesicoureteral reflux, and a right‐sided Morgagni‐type diaphragmatic hernia. G‐banded chromosome analysis revealed a deletion of 11p12‐p15.1. Breakpoint regions were refined by fluorescence in situ hybridization (FISH) and deletion of the WAGR critical region, including WT1, was confirmed. A review of the medical literature identified a second patient with a deletion of 11p13, a left‐sided Bochdalek‐type diaphragmatic hernia, and anomalies that suggest a diagnosis of WAGR including bilateral microphthalmia, a small penis, bilateral cryptorchidism, and a hypoplastic scrotum. These cases demonstrate that congenital diaphragmatic hernia can be associated with WAGR syndrome and suggest that deletions of WT1 may predispose individuals to develop congenital diaphragmatic hernia.

Interstitial deletion of 10p and atrial septal defect in DiGeorge 2 syndrome

We present molecular genetic investigations of a 4‐year‐old boy with craniofacial dysmorphism and developmental delay. Trivial mitral and tricuspid regurgitation without gross structural abnormality was diagnosed by echocardiography. High‐resolution chromosome analysis revealed an interstitial deletion, del(10)(p12.1p12.32). To characterize the deletion size and breakpoints, we performed fluorescence in situ hybridization analysis using 27 BAC clones. Our data demonstrate an approximately 5.5u2003Mb deletion del(10)(p12.1p12.31). Surprisingly, the BAC clone RP11‐56H7 that contains NEBL, an apparent downstream gene of the cardiogenic transcription factor HAND2 previously shown to be deleted in the patients with DiGeorge 2 syndrome and 10p13 deletion, was deleted in our patient with 10p12.1‐p12.31 deletion. In addition, we provide clinical data and results of molecular analysis for a patient with multiple congenital anomalies including Ebsteins anomaly, kidney malformations, and 10p13‐p14 deletion. We also reviewed 19 patients with congenital heart defects and deletions involving 10p and propose that atrial septal defect (ASD) is a common cardiac anomaly associated with DiGeorge 2 syndrome. Based on genotype–phenotype analysis of published patients and those reported herein, we propose an approximately 1.0u2003Mb critical region between loci D10S547 and D10S2176 in 10p14 to be associated with ASD. Considering that septal defects are the most frequent congenital heart anomaly, we suggest that further investigations in the 10p critical region are important to identify gene(s) responsible for this common birth defect.

Somatic mosaicism detected by exon-targeted, high-resolution aCGH in 10 362 consecutive cases

Somatic chromosomal mosaicism arising from post-zygotic errors is known to cause several well-defined genetic syndromes as well as contribute to phenotypic variation in diseases. However, somatic mosaicism is often under-diagnosed due to challenges in detection. We evaluated 10u2009362 patients with a custom-designed, exon-targeted whole-genome oligonucleotide array and detected somatic mosaicism in a total of 57 cases (0.55%). The mosaicism was characterized and confirmed by fluorescence in situ hybridization (FISH) and/or chromosome analysis. Different categories of abnormal cell lines were detected: (1) aneuploidy, including sex chromosome abnormalities and isochromosomes (22 cases), (2) ring or marker chromosomes (12 cases), (3) single deletion/duplication copy number variations (CNVs) (11 cases), (4) multiple deletion/duplication CNVs (5 cases), (5) exonic CNVs (4 cases), and (6) unbalanced translocations (3 cases). Levels of mosaicism calculated based on the array data were in good concordance with those observed by FISH (10–93%). Of the 14 cases evaluated concurrently by chromosome analysis, mosaicism was detected solely by the array in 4 cases (29%). In summary, our exon-targeted array further expands the diagnostic capability of high-resolution array comparative genomic hybridization in detecting mosaicism for cytogenetic abnormalities as well as small CNVs in disease-causing genes.

Recurrent SOX9 deletion campomelic dysplasia due to somatic mosaicism in the father.

Haploinsufficiency of SOX9, a master gene in chondrogenesis and testis development, leads to the semi‐lethal skeletal malformation syndrome campomelic dysplasia (CD), with or without XY sex reversal. We report on two children with CD and a phenotypically normal father, a carrier of a somatic mosaic SOX9 deletion. This is the first report of a mosaic deletion of SOX9; few familial CD cases with germline and somatic mutation mosaicism have been described. Our findings confirm the utility of aCGH and indicate that for a more accurate estimate of the recurrence risk for a completely penetrant autosomal dominant disorder, parental somatic mosaicism should be considered in healthy parents.