3-hydroxy-3-methylglutaric aciduria (HMG)
How is 3-Hydroxy-3-Methylglutaric Aciduria (HMG) inherited?
3-Hydroxy-3-methylglutaric aciduria is inherited in an autosomal recessive pattern. Each individual inherits one copy of every gene from their mother and one copy from their father. Autosomal recessive conditions are those in which both copies of a gene have a pathogenic variant or mutation. It is likely that one pathogenic variant came from the mother and the other pathogenic variant came from the father. Parents themselves are considered unaffected carriers. This means that they have one working copy of the HMGCL gene and one non-working copy of the HMGCL gene. Their one working copy of the HMGCL gene creates enough of the HMG CoA lyase enzyme for the parent to not have any symptoms.
Therefore, there is a 25% risk or 1 in 4 risk for both parents to pass on their non-working copies of the HMGCL gene. This risk exists for each pregnancy. There is a 50% or a 1 in 2 chance that only one parent would pass on a non-working copy of the HMGCL gene. These pregnancies or children would be unaffected carriers like their parents. Lastly, there is a 25% or 1 in 4 chance that both parents would pass on their working copies of the HMGCL gene and a child would not be a carrier or affected with HMG lyase deficiency.