Clinical - All individuals reported have severe expressive language delay, behavioural disturbance (hyperactivity, aggressive outbursts) and hypotonia. The facial dysmorphic features are subtle and variable. Overgrowth has been reported. Hypotonia, usually acquired rather than neonatal is a common feature, present in >80% in Luciani's series. Severe expressive speech delay is a constant feature. Behavioural disorders are generally present in children >1yr eg. hyperactivity, sleep disturbance. SHANK3 (also known as ProSAP2) regulates the structural organization of dendritic spines and is a binding partner of neuroligins; genes encoding neuroligins are mutated in autism and Asperger syndrome. Durand et al recently showed that mutation of a single copy of SHANK3 on chromosome 22q13 can result in language and/or social communication disorders. >This observation explains why 22q13 deletion syndrome, which includes haploinsufficiency for SHANK3, is characterised by a severe linguistic and/or social communication disorder. No apparent life-threatening organic abnormalities accompany the diagnosis of deletion 22q13 (Phelan).
Size of deletion - Deletions are extremely variable in size from 160kB to 9Mb in the series reported by Luciani. The minimal critical region, associated with a phenotype of mild global developmental delay and severe language impairment is distal to the ARSA probe that is used as a 22q control for del (22q11.2). Wilson compared clinical features to deletion size and showed few correlations. Some measures of developmental assessment did correlate to deletion size; however, all patients showed some degree of mental retardation and severe delay or absence of expressive speech, regardless of deletion size. Similarly, Koolen in a study of 9 patients with deletions varying between 3.3-8.4Mb found that global developmental delay and absent or severely delayed speech were observed in all patients, with hypotonia present in 8/9. Bonaglia et al (2005) identified a common breapoint within a 15bp repeat unit in the SHANK3 gene in 2 patients, identical to that previously reported by Wong et al in 1997. The 3 patients showed mental retardation and developmental delay with severely delayed or absent expressive speech reinforcing the observation that the main phenotypic determinants of 22q13 syndrome lie in the terminal 100kb of 22q.
Origin of deletion - Luciani found a strong excess of paternal origin for all classes of rearrangement
Expert advisor: - Prof. Orsetta Zuffardi, Genetica Medica, Universit???? di Pavia, Pavia, Italy
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