What is the role of genetic testing in the workup of focal muscular atrophy (FMA)?

Updated: Feb 20, 2018
  • Author: Sridharan Ramaratnam, MD, MBBS; Chief Editor: Helmi L Lutsep, MD  more...
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Bulbospinal muscular atrophy (ie, Kennedy disease) is associated with an increase in the number of polymorphic tandem CAG repeats in exon 1 of the AR gene on the proximal long arm at Xq11 locus.

The gene candidates for spinal muscular atrophy include the genes for the survival motoneuron (SMN) and the neuronal apoptosis inhibitory protein (NAIP). Both genes are duplicated on chromosome 5. Genetic mutations have been identified in the major motor neuron diseases, including ALS (SOD1 gene), the hereditary spastic paraplegias, and rarer conditions such as GM2 gangliosidosis (hexosaminidase A deficiency).

Patients with hereditary neuropathy with tendency to pressure palsies may have a deletion on chromosome 17p11.2.

Xp21 deletion may suggest a diagnosis of Becker muscular dystrophy when the patient presents clinically with a quadriceps myopathy.

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