[X chromosomal bulbospinal neuropathy (X-BSN, Kennedy syndrome): an illness with repetitive triplet sequences. Case report, differential diagnosis and molecular genetics aspects].

X-chromosomal recessive bulbospinal neuronopathy (X-BNS, Kennedy's disease) is an important differential diagnosis of amyotrophic lateral sclerosis. We present the data of ten own patients along with a review of the literature on this uncommon disease which is caused by an expanded CAG-repeat in the androgen receptor gene. This mutation probably affects the transcription regulating activity of the androgen receptor in neurons. Signs and symptoms of X-BSN can be derived from partial insensitivity for androgens and a mixed, mainly motor neuronopathy. The clinical diagnosis is based on: 1. lower motor neuron weakness of bulbar and proximal limb muscles with onset in the third to fifth decade, 2. cramps and pronounced fasciculations, particularly of facial muscles, 3. postural tremor, 4. diminished or absent sensory action potentials inspite of only minor sensory impairment, 5. gynecomastia, and 6. infertility, diabetes mellitus and hyperlipoproteinemia in a minority of cases. Unlike amyotrophic lateral sclerosis, disease progression is slow with barely shortened life expectancy, which should be stressed in patient counselling. Causal treatment is as yet unavailable but several aspects of palliative medicine should be considered.