Monoamine Oxidase Deficiency (MAO-D) is caused by genetic mutations or deletions in the DNA of the MAO A and / or MAO B genes. Both MAO A and B genes are located at position Xp11.3 on the X-Chromosome, and adjacent to each other.
How MAO Deficiency is Inherited:
• Children inherit one X chromosome from their mother and either an X or Y chromosome from their father.
For Sons:
• Sons get their X chromosome from their mother and a Y chromosome from their father.
• If the X from the mother is normal, the son will not have MAO deficiency.
• If the X from the mother is mutated, the son will have MAO deficiency.
For Daughters:
• Daughters get one X chromosome from each parent.
• The father always gives a normal X chromosome.
• Even if the mother’s X is mutated, the normal X from the father prevents MAO deficiency.
Key Takeaway:
• Only sons who inherit a mutated X from their mother will have MAO deficiency because they don’t have a second X to balance it out.