Aetiologic spectrum of mental retardation & developmental delay in India

Background & objectives: The aetiology of mental retardation is varied and difficult to establish. Reports from India on the spectrum of underlying causative conditions are lacking. This retrospective study was conducted to establish the various aetiologies of mental retardation (MR) and developmental delay (DD) in patients attending a medical genetics centre in north India and to assess the contribution of genetic disorders. Methods: This retrospective study was conducted at a tertiary care centre in north India. All patients attending the centre with MR or DD from January 2007 to December 2009 were included. The aetiology of MR/DD was ascertained after clinical assessment and targeted laboratory evaluation. The spectrum of causative conditions and contribution of genetic disorders was established. Results: A total of 338 patients were included in the study, of whom definite diagnosis was established in 253 (74.8%). The various aetiological categories were: chromosomal disorders in 112 (33.1%), non chromosomal syndromes in 32 (9.5%), neurometabolic disorders in 34 (10.1%), central nervous system structural defects in 25 (7.4%), cerebral palsy in 43 (12.7%) and environmental insults in 7 (2%). Eighty five patients (25.2%) had idiopathic mental retardation. A total of 196 (58%) patients had a genetic disorder as the cause of MR/DD. Interpretation & conclusions: The aetiology of MR/DD is varied and difficult to establish in a significant proportion of patients. Chromosomal and various monogenic disorders contribute to a large number of MR/DD cases and hence a genetic work up is essential for all such patients.