Scientists with the Indian Institute of Science (IISc) and the National Institute of Mental Health and Neurosciences (NIMHANS), Bangalore, have discovered a key gene behind microcephaly, a brain disorder.
Their findings have been published in the International Journal of Human Genetics. While Arun Kumar of the Department of Molecular Reproduction, Development and Genetics, IISc, is the lead author of the paper, Satish C Girimaji of the Department of Psychiatry, NIMHANS is a co-author.
The discovery may help develop a regular clinical screening tool to detect this severe disorder at the foetal stage itself, it is hoped.
Primary microcephaly (MCPH) is an autosomal-recessive congenital disorder characterized by smaller-than-normal brain size and mental retardation.
Typically, the brain of a microcephaly patient weighs 430 gm, whereas that of a normal person is 1,459 gm. Because of a smaller brain, the intelligent quotient for microcephaly patients ranges from mild (IQ 50-70) to severely (IQ 20-35) low. Though it is not fatal, patients remain mentally-challenged throughout their lives. Interestingly, a large number of microcephaly patients are found in Pakistan where they are dubbed "rat people," apparently because of their small brain.
Till now only four genes were known to cause this disease, which is hereditary. Now a fifth gene has been located.
"ASPM (one of the four already known genes) and STIL are important for Indian microcephaly patients," IISc geneticist Arun Kumar told Deccan Herald
Another gene, MCPH2, has been also found in a handful of Indian patients but other three genes have never been reported from India.
Researchers examined a large number of families in Bangalore, Mangalore, Mysore and places in Tamil Nadu. While doctors at the NIMHANS collected the blood, the analysis was carried out at the IISc.
Though there is no database, Kumar said the prevalence of the disorder could be one child per every 50,000 to 100,000 live births.
So far, though microcephaly can be diagnosed in the embryo, the results are not reliable until the third trimester. The problem is at such a late stage, even if a mother knows that her foetus is having microcephaly, she cannot abort because it is illegal and dangerous.
Besides its clinical significance, the discovery bears significance in the study of human brain evolution from the days of early hominids like Australopithecus.
Mutations in STIL (and in other four known genes) may help researchers understand evolution in the human brain. Primitive man like Australopithecus had small brain (450 gm), which is similar to the brains of microcephaly patients.
The genes could provide hints to how the cerebral cortex - the core of human brain - evolved faster to reach the present level, Arun Kumar added.