Smith-Magenis syndrome (SMS) is a complex disorder whose clinical features include mild to severe intellectual disability with speech delay, growth failure, brachycephaly, flat midface, short broad hands, and behavioral problems. SMS is typically caused by a large deletion on 17p11.2 that encompasses multiple genes including the retinoic acid induced 1, RAI1, gene or a mutation in the RAI1 gene. Here we have evaluated 30 patients with suspected SMS and identified SMS-associated classical 17p11.2 deletions in six patients, an atypical deletion of B139 kb that partially deletes the RAI1 gene in one patient, and RAI1 gene nonsynonymous alterations of unknown significance in two unrelated patients. The RAI1 mutant proteins showed no significant alterations in molecular weight, subcellular localization and transcriptional activity. Clinical features of patients with or without 17p11.2 deletions and mutations involving the RAI1 gene were compared to identify phenotypes that may be useful in diagnosing patients with SMS. European Journal of Human Genetics (2012) 20, 148-154; doi:10.1038/ejhg.2011.167; published online 7 September 2011Keywords: Smith-Magenis syndrome; 17p11.2; RAI1; arrayCGH; mutation; deletion INTRODUCTION Smith-Magenis syndrome (SMS, MIM 182290) is a multiple congenital anomalies and intellectual disability syndrome associated with a deletion of chromosome 17p11. 2. The incidence of SMS is estimated to be B1:15 000-1:25 000 births. 1 SMS is most commonly characterized by a variable degree of intellectual disability including speech and motor delay, craniofacial and skeletal anomalies, sleep disturbance, self-injurious and attention-seeking behaviors. 1,2 Craniofacial features include brachycephaly, midface hypoplasia, tented upper lip, relative prognathism with age and deep-set and hypoteloric eyes. 3,4 Skeletal features include brachydactyly, short stature and short/ broad hands. 3,4 The behavioral phenotype includes onychotillomania, polyembolokoilamania, 'hand licking and page flipping' , 'self-hugging' and hyperactivity. 5 Sleep disturbance is present in 88% of SMS patients and is characterized by difficulty getting to sleep, frequent nocturnal awakenings, early sleep offset and daytime sleepiness with a need for daytime naps. 6,7 SMS clinical features overlap with other intellectual disability syndromes such as Prader-Willi, Williams and Down's syndromes, which often complicate its clinical diagnosis.A majority, B90%, of SMS patients have a deletion of chromosome 17p11.2 that includes the RAI1 gene. 3 The classical SMS deletions span B3.5 Mb of 17p11.2 and are present in B70% of affected individuals.
ABSTRACT. Smith-Magenis syndrome (SMS) is a complex congenital anomaly characterized by craniofacial anomalies, neurological and behavioral disorders. SMS is caused by a deletion in region 17p11.2, which includes the RAI1 gene (90% of cases), or by point mutation in the RAI1 gene (10% of cases). Laboratory diagnosis is through cytogenetic analysis by GTG banding and molecular cytogenetic analysis by FISH. We carried out an active search for patients in Associations of Parents and Friends of Exceptional Children (APAE) of São Paulo and genetic centers in Brazil. Forty-eight patients were screened for mental retardation, craniofacial abnormalities and stereotyped behavior with a diagnosis of SMS. In seven of them, chromosome banding at high resolution demonstrated chromosome 17p11.2 deletions, confirmed by FISH. We also made a meta-analysis of 165 cases reported between 1982 and 2010 to compare with the clinical data of our sample. We demonstrated differences between the frequencies of clinical signs among the cases reported and seven Brazilian cases of this study, such as dental anoma- Brazilian cases of Smith-Magenis syndrome lies, strabismus, ear infections, deep hoarse voice, hearing loss, and cardiac defects. Although the gold standard for diagnosis of SMS is FISH, we found that the GTG banding technique developed to evaluate chromosome 17 can be used for the SMS diagnosis in areas where the FISH technique is not available.
Terminal deletion in the short arm of chromosome 1 results in a disorder described as 1p36 deletion syndrome. The resulting phenotype varies among patients including mental retardation, developmental delay, sensorineural hearing loss, seizures, heart defects, and distinct facies. In the present case, we performed array-comparative genomic hybridization in a boy with multiple congenital malformations presenting some features overlapping the 1p36 deletion phenotype for whom chromosomal analysis did not reveal a terminal deletion in 1p. Results showed complex chromosome rearrangements involving the 1p36.33-p35.3 region. While the mechanism of origin of these rearrangements is still unclear, chromothripsis-a single catastrophic event leading to shattering chromosomes or chromosome regions and rejoining of the segments-has been described to occur in a fraction of cancers. The presence of at least 12 clustered breaks at 1p and apparent lack of mosaicism in the present case suggests that a single event like chromothripsis occurred. This finding suggests that chromothripsis is responsible for some constitutive complex chromosome rearrangements.
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