What Your Test Results Mean:

Carriers typically show no symptoms of MLC; however, carriers are at an increased risk of having a child with MLC. Risk for the current or future pregnancies is dependent on your partner’s carrier status. Carrier testing of your partner is recommended in addition to consultation with a genetic counselor for more detailed risk assessment.

Disease Explained:

MLC is an inherited brain disorder that causes progressive neurological complications. Affected individuals are born with enlarged heads (megalencephaly) and abnormalities in the brain’s white matter (myelin, which insulates and protects nerve fibers). They may have mild developmental delays early in life but over time, the white matter wastes away causing increased muscle spasticity, difficulty coordinating movements, and mild to moderate intellectual disability. Some affected individuals also experience seizures, poor muscle tone, and difficulties talking and swallowing. Treatment is supportive and most individuals with MLC live well into adulthood, though they may lose their ability to walk independently.

How the Genetics Works:

The majority of MLC is caused by pathogenic variants in the MLC1 gene. In general, individuals have two copies of the MLC1 gene. Carriers of MLC have a single variant in one copy of the MLC1 gene while individuals with MLC have variants in both copies of their genes, one inherited from each parent. Risk for two carriers to have a child with MLC is 25%.