Congenital hypothyroidism is one of the most common, preventable causes of mental retardation. Worldwide, congenital hypothyroidism affects one in 3,800 newborn babies on an average. Studies from Mumbai indicate it might be more common in India, with the disease occurring in one in 2,640 neonates, said Mediscan System director, Dr S Suresh.

In congenital hypothyroidism, the child suffers from mental retardation, and below-normal physical growth. If left untreated, the damage becomes irreversible. "When diagnosed early and treated adequately, children born with congenital hypothyroidism can experience normal physical growth and neurological development," he added.

Paediatrician Dr Sudha said most newborn babies with congenital hypothyroidism appear normal at birth, even if there is complete lack of development of the thyroid gland. This is because a small amount of thyroid hormone (T4) from the mother is transferred to the baby during pregnancy. Once a baby is diagnosed with congenital hypothyroidism, the baby is started on thyroid hormone replacement.

"Most of the children with congenital hypothyroidism need to take thyroid hormones for the rest of their lives. Early diagnosis and adequate treatment from the first weeks of life result in normal growth and intelligence," she added.

Sudha said most cases cannot be prevented. "However, there can be some modifiable causative factors like the mother taking anti-thyroid medications, or too much or too little iodine. In such cases, the doctor might be able to give appropriate advice," she said.