BackgroundInterstitial Microdeletion and Microduplication syndromes have been proposed as a significant cause of sporadic intellectual disability (ID) but the role of such aberrations in familial ID has not yet been investigated. As the balanced chromosomal abnormalities commonly lead to the recurrent ID or multiple congenital anomalies, this study was designed to evaluate whether it was justified to investigate such aberrations in familial ID patients. Three hundred and twenty eight patients from 101 unrelated Iranian families with more than two ID patients in the first-degree relatives, have been investigated. Assessment of a panel of 21 common Microdeletion and Microduplication syndromes (CMMS) was carried out using Multiplex Ligation-Dependent Probe Amplification (MLPA) technique.ResultsAmong the families studied, 27.7% had 4-12, 35.6% had 3 and 36.6% had 2 affected individuals in the first-degree relatives. An autosomal dominant inheritance of Williams-Beuren syndrome (WBS) was detected in a family with no clinical suspicion of WBS. The prevalence of CMMS was therefore,0.99%.ConclusionThis is the first investigation of a panel of CMMS in a large sample set of "familial ID patients". The findings of this study showed the low prevalence of CMMSs in "familial ID" patients in spite of the significant contribution of such aberrations in "sporadic ID" which has a very useful practical impact by avoiding unnecessary diagnostic tests in "familial ID" patients.
Williams-Beuren syndrome (WBS), a contiguous gene deletion syndrome, mostly occurs sporadically. Although a few cases of familial WBS have been reported in the literature, molecular confirmation of the deletion has not been carried out in all of them. Here, we report on the eighth clinically and molecularly confirmed inherited WBS detected in a family with 'familial mental retardation.' A comprehensive screening approach to mental retardation that included stepwise karyotyping, assessment for fragile-X syndrome, subtelomeric rearrangements and known microdeletion/microduplication syndromes, and a genome-wide array-CGH study was applied. The father, the mother, and their daughter were all mentally handicapped with nonspecific clinical manifestations and dysmorphic features. The first child of the family died from multiple congenital anomalies. The father and his daughter, who had never been suspected to have WBS, were diagnosed as having a deletion of the WBS critical region. No other abnormalities were detected in the family. Unlike other previously reported cases, in which the disease was ascertained on the basis of clinical manifestations, the present report represents an example of the detection of cryptic chromosomal abnormalities in mental retardation patients by the stepwise application of high-throughput screening methods.
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