Q: What type of tests could be done to check whether my children are at risk for muscular dystrophy? My husband comes from a family of six children, two of whom have limb-girdle muscular dystrophy. He doesn’t have it though. Does a female have a greater chance of passing on the gene to her child?
A: The genetics of limb-girdle muscular dystrophy haven’t been sorted out completely yet. Several chromosomal loci have been identified for autosomal dominant (5q [no known gene product]) and recessive (2q, 4q [beta-sarcoglycan], 13q [gamma-sarcoglycan], 15q [calpain, a calcium-activated protease], and 17q [alpha-sarcoglycan, or adhalin]) forms.
Autosomal dominant means that a person only needs one abnormal allele of a gene for it to lead to an autosomal dominant disorder.
In general, the following rules apply:
1. An affected person has an affected parent.
2. An affected person and an unaffected person have, on average, an equal number of affected and unaffected children.
3. Unaffected children of an affected parent have unaffected children and grandchildren.
4. Males and females are equally likely to be affected.
5. The risk for occurrence among children of an affected person is 50%.
In an autosomal recessive disorder, the following rules of inheritance apply:
1. Normal parents have an affected child, both parents are heterozygotes, and, on average, 1/4 of their children will be affected, 1/2 will be heterozygotes, and 1/4 will be normal.
2. All children of an affected person and a genotypically normal person will be phenotypically normal heterozygotes.
3. On average, 1/2 the children of an affected person and a heterozygote will be affected, and 1/2 will be heterozygotes.
4. All children of two affected persons will be affected.
5. Males and females are equally likely to be affected.
6. Heterozygotes are phenotypically normal but are carriers of the trait. If the disease is caused by a defect of a specific protein (e.g. an enzyme), the carrier usually has a reduced amount of that protein. If the mutation is known, molecular genetic techniques can identify heterozygous phenotypically normal persons.
So, the chance of your children being affected is remote, but you can have your husband tested to find out whether he is a carrier, or not.
Best of luck!