Metachromatic Leukodystrophy - Genetics

Genetics

MLD has an autosomal recessive inheritance pattern. The inheritance probabilities per birth are as follows:

• If both parents are carriers:
  • 25% (1 in 4) children will have the disorder
  • 50% (2 in 4) children will be carriers (but unaffected)
  • 25% (1 in 4) children will be free of MLD - unaffected child that is not a carrier

• If one parent is affected and one is free of MLD:
  • 0% (0) children will have the disorder - only one parent is affected, other parent always gives normal gene
  • 100% (4 in 4) children will be carriers (but unaffected)

• If one parent is a carrier and the other is free of MLD:
  • 50% (2 in 4) children will be carriers (but unaffected)
  • 50% (2 in 4) children will be free of MLD - unaffected child that is not a carrier

In addition to these frequencies there is a 'pseudo'-deficiency that affects 7%-15% of the population. People with the pseudo deficiency do not have any MLD problems unless they also have affected status. With the current diagnostic tests, Pseudo-deficiency reports as low enzyme levels but sulfatide is processed normally so MLD symptoms do not exist.

For further information, see recessive gene and dominance relationship. Also, consult the MLD genetics page at the MLD Foundation.