Spinal and Bulbar Muscular Atrophy - Clinical Features and Pathogenesis

Clinical features SBMA, or Kennedy’s disease, is an inherited lower motor neuron disease characterised by adult-onset muscle atrophy, weakness, contraction, fasciculations, and bulbar involvement. The onset of weakness is usually between 30 and 50 years, but often preceded by nonspecific symptoms such as tremor, muscle cramps and fatigue. Muscle atrophy and weakness are predominant in the tongue and proximal musculature. Deep tendon reflex is diminished or absent with no pathological reflex. Sensory involvement is largely restricted to vibration sense which is affected distally in the legs. Male patients often demonstrate signs of androgen insensitivity such as gynecomastia, testicular atrophy, impotence and decreased fertility, some of which are detected before the onset of motor symptoms. Hyperlipidemia, liver dysfunction and glucose intolerance are also seen in some cases. SBMA chiefly affects males, whereas females with the mutation are usually asymptomatic even when homozygous. The prevalence of SBMA has been estimated 1 in 40000 in areas with high ascertainment, although a considerable number of patients may have been under diagnosed. The disease progresses slowly in general, although repetitive respiratory tract infection often occurs in the advanced stage of the disease, resulting in early death in some patients. No specific treatment for SBMA has been established. Testosterone has been used in some patients, although it has no effects on the progression of SBMA.