O Raoul

Array-based comparative genomic hybridisation identifies high frequency of cryptic chromosomal rearrangements in patients with syndromic autism spectrum disorders

Background: Autism spectrum disorders (ASD) refer to a broader group of neurobiological conditions, pervasive developmental disorders. They are characterised by a symptomatic triad associated with qualitative changes in social interactions, defect in communication abilities, and repetitive and stereotyped interests and activities. ASD is prevalent in 1 to 3 per 1000 people. Despite several arguments for a strong genetic contribution, the molecular basis of a most cases remains unexplained. About 5% of patients with autism have a chromosome abnormality visible with cytogenetic methods. The most frequent are 15q11–q13 duplication, 2q37 and 22q13.3 deletions. Many other chromosomal imbalances have been described. However, most of them remain undetectable using routine karyotype analysis, thus impeding diagnosis and genetic counselling. Methods and results: 29 patients presenting with syndromic ASD were investigated using a DNA microarray constructed from large insert clones spaced at approximately 1 Mb intervals across the genome. Eight clinically relevant rearrangements were identified in 8 (27.5%) patients: six deletions and two duplications. Altered segments ranged in size from 1.4 to 16 Mb (2–19 clones). No recurrent abnormality was identified. Conclusion: These results clearly show that array comparative genomic hybridisation should be considered to be an essential aspect of the genetic analysis of patients with syndromic ASD. Moreover, besides their importance for diagnosis and genetic counselling, they may allow the delineation of new contiguous gene syndromes associated with ASD. Finally, the detailed molecular analysis of the rearranged regions may pave the way for the identification of new ASD genes.

Spectrum of NSD1 mutations in Sotos and Weaver syndromes

Sotos syndrome is an overgrowth syndrome characterised by pre- and postnatal overgrowth, macrocephaly, advanced bone age, and typical facial features. Weaver syndrome is a closely related condition characterised by a distinctive craniofacial appearance, advanced carpal maturation, widened distal long bones, and camptodactyly. Haploinsufficiency of the NSD1 gene has recently been reported as the major cause of Sotos syndrome while point mutations accounted for a minority of cases. We looked for NSD1 deletions or mutations in 39 patients with childhood overgrowth. The series included typical Sotos patients (23/39), Sotos-like patients (lacking one major criteria, 10/39), and Weaver patients (6/39). We identified NSD1 deletions (6/33) and intragenic mutations (16/33) in Sotos syndrome patients. We also identified NSD1 intragenic mutations in 3/6 Weaver patients. We conclude therefore that NSD1 mutations account for most cases of Sotos syndrome and a significant number of Weaver syndrome cases in our series. Interestingly, mental retardation was consistently more severe in patients with NSD1 deletions. Macrocephaly and facial gestalt but not overgrowth and advanced bone age were consistently observed in Sotos syndrome patients. We suggest therefore considering macrocephaly and facial gestalt as mandatory criteria for the diagnosis of Sotos syndrome and overgrowth and advanced bone age as minor criteria.

Automated fluorescent genotyping detects 10% of cryptic subtelomeric rearrangements in idiopathic syndromic mental retardation

Recent studies have shown that cryptic unbalanced subtelomeric rearrangements contribute to a significant proportion of idiopathic syndromic mental retardation cases. Using a fluorescent genotyping based strategy, we found a 10% rate of cryptic subtelomeric rearrangements in a large series of 150 probands with severe idiopathic syndromic mental retardation and normal RHG-GTG banded karyotype. Fourteen children were found to carry deletions or duplications of one or more chromosome telomeres and two children had uniparental disomy. This study clearly shows that fluorescent genotyping is a sensitive and cost effective method that not only detects cryptic subtelomeric rearrangements but also provides a unique opportunity to detect uniparental disomies. We suggest giving consideration to systematic examination of subtelomeric regions in the diagnostic work up of patients with unexplained syndromic mental retardation.

Cryptic terminal deletion of chromosome 9q34: a novel cause of syndromic obesity in childhood?

Obesity is a symptom of diagnostic value in multiple congenital anomaly-mental retardation syndromes. While acquired non-specific weight gain related to drug intake or associated behavioural disorders occasionally occurs in the course of mental retardation, obesity is known to be a specific feature of several well defined conditions, including Bardet-Biedl syndrome, Prader-Willi syndrome, Cohen syndrome, fragile X syndrome, and several chromosomal anomalies. Yet a number of mentally retarded children with apparently early onset weight gain remain undiagnosed. Here, we report on a de novo deletion of chromosome 9q34 in two unrelated mentally retarded children with early onset obesity, distinctive facial features (brachycephaly, synophrys, anteverted nostrils, prognathism), sleep disturbances, and behavioural problems. FISH and microsatellite DNA analyses showed that the two children carried a similar small deletion (3 Mb) of the terminal long arm of chromosome 9 (del 9q34). We suggest therefore that the del 9q34 is a novel cause of syndromic obesity and mental retardation. Its association with distinctive facial features and behavioural problems should help in recognising this novel phenotype. Based on this observation, we suggest giving consideration to cryptic deletions of chromosome 9q34 in the diagnosis of unexplained obesity/mental retardation syndromesnn### Case 1nnA boy was born to unrelated, healthy parents after a term pregnancy and normal delivery (birth weight 3200 g, length 50 cm, OFC 34.5 cm). He was hypotonic in the first months of life but no feeding difficulties were originally noted. Excessive weight gain with increased appetite and food seeking behaviour were noted at 30 months of age. At 5 years, his weight was 26 kg (>+3 SD), length 112 cm (+1 SD), and OFC 48 cm (−2 SD) and at 9 years his weight was 72 kg (>+ 6 SD), length 144 cm (+2 SD), and OFC 52.5 cm (−0.5 SD) (figs 1A–C and 2A). Distinctive facial …

Comparative genomic hybridisation in mentally retarded patients with dysmorphic features and a normal karyotype.

Segmental aneusomy for small chromosomal regions has been shown to be a common cause of mental retardation and multiple congenital anomalies. A screening method for such chromosome aberrations that are not detected using standard cytogenetic techniques is needed. Recent studies have focused on detection of subtle terminal chromosome aberrations using subtelomeric probes. This approach however excludes significant regions of the genome where submicroscopic rearrangements are also liable to occur. The aim of the present study was to evaluate the efficiency of comparative genomic hybridisation (CGH) for screening of submicroscopic chromosomal rearrangements. CGH was performed in a cohort of 17 patients (14 families) with mental retardation, dysmorphic features and a normal karyotype. Five subtle unbalanced rearrangements were identified in 7 patients. Subsequent FISH studies confirmed these results. Although no interstitial submicroscopic rearrangement was detected in this small series, the study emphasises the value of CGH as a screening approach to detect subtle chromosome rearrangements in mentally retarded patients with dysmorphic features and a normal karyotype.

19q13.11 deletion syndrome: a novel clinically recognisable genetic condition identified by array comparative genomic hybridisation

Background: Deletions of chromosome 19 have rarely been reported, with the exception of some patients with deletion 19q13.2 and Blackfan–Diamond syndrome due to haploinsufficiency of the RPS19 gene. Such a paucity of patients might be due to the difficulty in detecting a small rearrangement on this chromosome that lacks a distinct banding pattern. Array comparative genomic hybridisation (CGH) has become a powerful tool for the detection of microdeletions and microduplications at high resolution in patients with syndromic mental retardation. Methods and results: Using array CGH, this study identified three interstitial overlapping 19q13.11 deletions, defining a minimal critical region of 2.87 Mb, associated with a clinically recognisable syndrome. The three patients share several major features including: pre- and postnatal growth retardation with slender habitus, severe postnatal feeding difficulties, microcephaly, hypospadias, signs of ectodermal dysplasia, and cutis aplasia over the posterior occiput. Interestingly, these clinical features have also been described in a previously reported patient with a 19q12q13.1 deletion. No recurrent breakpoints were identified in our patients, suggesting that no-allelic homologous recombination mechanism is not involved in these rearrangements. Conclusions: Based on these results, the authors suggest that this chromosomal abnormality may represent a novel clinically recognisable microdeletion syndrome caused by haploinsufficiency of dosage sensitive genes in the 19q13.11 region.

Phenotype-Genotype Correlations in 17 New Patients with an Xp11.23p11.22 Microduplication and Review of the Literature

Array comparative genomic hybridization (array CGH) has proven its utility in uncovering cryptic rearrangements in patients with X‐linked intellectual disability. In 2009, Giorda et al. identified inherited and de novo recurrent Xp11.23p11.22 microduplications in two males and six females from a wide cohort of patients presenting with syndromic intellectual disability. To date, 14 females and 5 males with an overlapping microduplication have been reported in the literature. To further characterize this emerging syndrome, we collected clinical and microarray data from 17 new patients, 10 females, and 7 males. The Xp11.23p11.2 microduplications detected by array CGH ranged in size from 331u2009Kb to 8.9u2009Mb. Five patients harbored 4.5u2009Mb recurrent duplications mediated by non‐allelic homologous recombination between segmental duplications and 12 harbored atypical duplications. The chromosomal rearrangement occurred de novo in eight patients and was inherited in six affected males from three families. Patients shared several common major characteristics including moderate to severe intellectual disability, early onset of puberty, language impairment, and age related epileptic syndromes such as West syndrome and focal epilepsy with activation during sleep evolving in some patients to continuous spikes‐and‐waves during slow sleep. Atypical microduplications allowed us to identify minimal critical regions that might be responsible for specific clinical findings of the syndrome and to suggest possible candidate genes: FTSJ1 and SHROOM4 for intellectual disability along with PQBP1 and SLC35A2 for epilepsy. Xp11.23p11.22 microduplication is a recently‐recognized syndrome associated with intellectual disability, epilepsy, and early onset of puberty in females. In this study, we propose several genes that could contribute to the phenotype.

Genome‐wide screening using automated fluorescent genotyping to detect cryptic cytogenetic abnormalities in children with idiopathic syndromic mental retardation

Mental retardation (MR) is the most common developmental disability, affecting approximately 2% of the population. The causes of MR are diverse and poorly understood, but chromosomal rearrangements account for 4–28% of cases, and duplications/deletions smaller than 5u2003Mb are known to cause syndromic MR. We have previously developed a strategy based on automated fluorescent microsatellite genotyping to test for telomere integrity. This strategy detected about 10% of cryptic subtelomeric rearrangements in patients with idiopathic syndromic MR. Because telomere screening is a first step toward the goal of analyzing the entire genome for chromosomal rearrangements in MR, we have extended our strategy to 400 markers evenly distributed along the chromosomes to detect interstitial anomalies. Among 97 individuals tested, three anomalies were found: two deletions (one in three siblings) and one parental disomy. These results emphasize the value of a genome‐wide microsatellite scan for the detection of interstitial aberrations and demonstrate that automated genotyping is a sensitive method that not only detects small interstitial rearrangements and their parental origin but also provides a unique opportunity to detect uniparental disomies. This study will hopefully contribute to the delineation of new contiguous gene syndromes and the identification of new imprinted regions.