Spinal and bulbar muscular atrophy

Spinal and bulbar muscular atrophy (SBMA), popularly known as Kennedy's disease, is a progressive debilitating neurodegenerative disorder resulting in muscle cramps and progressive weakness due to degeneration of motor neurons in the brainstem and spinal cord.Muscular Spinal and bulbar muscular atrophy (SBMA), popularly known as Kennedy's disease, is a progressive debilitating neurodegenerative disorder resulting in muscle cramps and progressive weakness due to degeneration of motor neurons in the brainstem and spinal cord. The condition is associated with mutation of the androgen receptor (AR) gene and is inherited in an X-linked recessive manner. As with many genetic disorders, no cure is known, although research continues. Because of its endocrine manifestations related to the impairment of the AR gene, SBMA can be viewed as a variation of the disorders of the androgen insensitivity syndrome (AIS). It is also related to other neurodegenerative diseases caused by similar mutations, such as Huntington's disease. Individuals with SBMA have muscle cramps and progressive weakness due to degeneration of motor neurons in the brain stem and spinal cord. Ages of onset and severity of manifestations in affected males vary from adolescence to old age, but most commonly develop in middle adult life. The syndrome has neuromuscular and endocrine manifestations. Early signs often include weakness of tongue and mouth muscles, fasciculations, and gradually increasing weakness of limb muscles with muscle wasting. Neuromuscular management is supportive, and the disease progresses very slowly, but can eventually lead to extreme disability. Further signs and symptoms include: Homozygous females, both of whose X chromosomes have a mutation leading to CAG expansion of the AR gene, have been reported to show only mild symptoms of muscle cramps and twitching. No endocrinopathy has been described. The genetics of spinal and bulbar muscular atrophy have to do with the mutated androgen receptor gene located on the X chromosome. The effects of the mutation may be androgen-dependent, thus only males are fully affected. Females are rarely affected; female carriers tend to have a relatively mild expression of the disease if they show symptoms at all. The mechanism behind SBMA is caused by expansion of a CAG repeat in the first exon of the androgen receptor gene (trinucleotide repeats). The CAG repeat encodes a polyglutamine tract in the androgen receptor protein. The greater the expansion of the CAG repeat, the earlier the disease onset and more severe the disease manifestations. The repeat expansion likely causes a toxic gain of function in the receptor protein, since loss of receptor function in androgen insensitivity syndrome does not cause motor neuron degeneration. Spinal and bulbar muscular atrophy may share mechanistic features with other disorders caused by polyglutamine expansion, such as Huntington's disease. No cure for SBMA is known. In regards to the diagnosis of spinal and bulbar muscular atrophy, the AR Xq12 gene is the focus. Many mutations are reported and identified as missense/nonsense, that can be identified with 99.9% accuracy. Test for this gene in the majority of affected patients yields the diagnosis.