"Familial" versus "Sporadic" intellectual disability: contribution of common microdeletion and microduplication syndromes

Among 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%.This 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.Intellectual Disability, formerly Mental Retardation, is caused by heterogeneous genetic and non-genetic causes and affects 1-3% of the general population [1,2]. Regarding the heavy burden of ID, familial ID imposes much more burden on the affected families, society and health care system. Therefore, determining a specific genetic diagnosis facilitates both comprehensive medical care and accurate recurrence risk assessment for the family. As familial ID has a much lower incidence in western countries, its genetic basis has not been investigated to the extent of sporadic ID. Familial ID could be due to both chromosomal abnormalities and single gene disorders. In recent years the genetic basis of X-linked and autosomal recessive ID (ARID) has been thoroughly investigated and has lead to the identification of new genes and mutations [3-6]. However, no large scale study has so far been conducted to delineate the other underlying genetic causes of familial ID.Chromosomal aberrations are considered to be the most frequent cause of unexplained developmental delay (DD), ID and multiple congenital anomalies (MCA) [7,8]. Emerging new molecular cytogenetic techniques like fluorescence in situ hybridization (FISH), multiplex ligation-dependent probe amplification (MLPA) and array-based whole genome screening has shown tha