The secrets of mental retardation revealed: Scientists say mothers pass on mental retardation gene to offspring

By Syed Akbar

Hyderabad: City geneticists have found that mutations in X

chromosomes, contributed by mother, will lead to mental retardation in children.

A joint study by L Hemabindu, PP Reddy and others from the department of

environmental toxicology, Institute of Genetics and Hospital for Genetic Diseases,

Osmania University, detected L1 CAM mutations in X-linked mental retardation. L1 CAM is a

neural cell adhesion molecule (CAM) belonging to the superfamily of the immunoglobulins and is

critical for proper central nervous system development in humans. Since mutations on X

chromosome is now linked to mental retardation, it simply means that mothers pass on the

defect to their children.

The research team screened as many as 15 cases with mental retardation

analysing genomic DNA from the patients and control subjects. The team detected mutations in

two out of 15 patients. "It is worthwhile to screen idiopathic mental retardation cases

for L1 CAM mutations to reduce genetic morbidity in the population by offering genetic counselling

and prenatal diagnosis," the study pointed out.

Mental retardation is caused by genetic and non-genetic factors. Among the

genetic factors, chromosomal anomalies and metabolic disorders were found to be causative

factors in 50 per cent of the cases with mental retardation. However in the remaining 50 per

cent of cases, the cause is not established.

Studies conducted in the field of molecular genetics and developmental

neurobiology revealed that some types of brain malformations and mental retardation are due to

mutations in L1 gene. Cell adhesion molecule (L1CAM) plays a key role in the development of

nervous system. The gene encoding L1 is located on the X chromosome.

Patients suspected for mental retardation from different hospitals and clinics were referred to the Institute of

Genetics and Hospital for Genetic Diseases for confirmation. After initial examination, unknown

cases of mental retardation were included for the study. Fifteen children in the age group

of 6 months to 15 years were selected. For comparison, an equal number of healthy and normal

children in the same age group and socio-economic status were selected as controls.

The patients and the healthy subjects were clinically examined and

information on their age, sex, physical features, pedigree and health status was recorded in a

standard questionnaire. Psychological assessment was performed using standard IQ assessment tests.