| Mental retardation is the most common plague of mankind. It is a lifelong disease characterised by impairment of cognitive and adaptive skills. More than any other type of disorder, mental retardation has a predominating effect on the life of the patient and the relatives. Thus, mental retardation lays an unrivalled burden on society. Estimates regarding its frequency vary, but it is generally quoted that it affects one to three per cent of the population (1).The causes of the developmental delay are extremely heterogeneous, and although half of the mental retardation cases are of unknown etiology today, it has been estimated that half of all cases are due to environmental factors and the remaining half to genetic factors. Environmental factors include exposure to toxic substances (such as alcohol or drugs), radiation, infection and so on during pregnancy. |
