Identification of a base pair deletion within exon 10 of the HK gene. The amplified PCR fragments of exon 10 from normal human, the propositus', and all family members' DNA underwent direct nucleotide sequencing. The propositus exhibited a homozygous base pair deletion of an adenine at nucleotide position 367 in exon 10 (corresponding to position 1492 of the full-length mRNA and position 480 of the mature protein). All family members were heterozygous for the same defect in the PCR of their amplified DNA.