ARMS-PCR products of 172 bp obtained using the normal and mutant forward primers. All relations are defined with respect to the patient. N, normal forward primer; M, mutant forward primer. The molecular weight marker used is the 100-bp ladder (BRL). Only the mutant primer gives a PCR product from the patient, indicating that the patient is mutant homozygous. Both the normal and mutant primers give PCR products from the mother, brother, and daughter, suggesting that they are all heterozygous for this mutation. The father, wife, and unrelated normal control give a PCR product with the normal primer but not with the mutant primer, confirming that they are normal homozygous. This latter pattern was obtained from all the 124 normal controls analyzed.