Kennedy-Alter-Sung (KAS) disease is a hereditary lower motor neuron disease. In this study, we investigated 2 KAS patients presenting with progressive muscle weakness and wasting, action tremor, perioral fasciculation and gynecomastia. Three carriers and 5 healthy members from this 3-generation KAS Chinese family and 60 normal Chinese controls were included in this study. Hormone studies revealed normal serum level in thyrotropin, prolactin, testosterone, leuteinizing hormone, follicle stimulating hormone, and estradiol. Lipid study disclosed type IV hyperlipoproteinemia in 2 KAS patients and 3 healthy members. Molecular studies revealed that the number of CAG triplet repeats in the first exon of androgen receptor gene of the normal allele is in the range of 15-19 and 12-25 in this family and normal controls, respectively. However, the number of CAG repeat of androgen receptor gene were unstable in the mutant alleles with a range of 41-4.5 and increased from generation to generation (genomic anticipation) in the 2 KAS patients and 3 female carriers. We conclude that the CAG triplet repeats in mutant alleles were unstable in the family with the KAS disease. Furthermore, type IV hyperlipoproteinemia may be a co-transmitted syndrome in the family with I KAS disease.