What is Megalencephaly

Megalencephaly is a rare condition in which a baby or a child develops an abnormally large brain. While a normal adult brain weighs between 1, 300 and 1, 400 grams, a megalencephalic brain weighs more than 1, 600 grams. A baby may be born with megalencephaly or might develop it over time. Though rare, but the condition may cause the brain to weigh twice more than the actual weight.

Megalencephaly if occurs alone, may or may not show any symptoms. It may also occur with a wide range of neurological problems and/or birth defects. It is often confused with macrocephaly, which is characterised by a large head, which may not necessarily be abnormal.

Types of Megalencephaly

This condition has three broad types.

• primary megalencephaly, or benign familial megalencephaly
• secondary megalencephaly, which occurs as the result of another disorder
• unilateral megalencephaly, or hemimegalencephaly, which is the enlargement of one half of the brain and is very rare

Causes of Megalencephaly

Megalencephaly is caused by defects in the way the brain controls cell production. When the brain is normal, the correct number of cells grow in the right place at the right time. But when the brain produces too many cells or cells that are too large, megalencephaly occurs. An abnormal collection of metabolic byproducts and matter can also cause megalencephaly.

Genetic factors can cause the condition. It can also result from genetic conditions of the nervous system. These include:

• Alexander disease
• neurofibromatosis
• tuberous sclerosis
• overgrowth disorders, like Sotos syndrome and Beckwith-Wiedemann syndrome.
• chromosomal disorders, like Klinefelter syndrome

Non-genetic causes include disorders of the cerebral spinal fluid. And sometimes there is no known cause.

Males are at an increased risk of three to four times of having megalencephaly than women. It affects between 10 and 30 percent of patients with macrocephaly (CPN). Asymptomatic cases may not be reported, so the exact incidence is not clear.

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