What is the role of genetic testing in the workup of spinal muscular atrophy (SMA)?

Updated: May 29, 2019
  • Author: Jeffrey Rosenfeld, MD, PhD, FAAN; Chief Editor: Stephen L Nelson, Jr, MD, PhD, FAACPDM, FAAN, FAAP  more...
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Answer

Both prenatal and postnatal tests are now commercially available.

Homozygous SMN1 gene deletion is 95% sensitive and nearly 100% specific for the diagnosis of SMA. In patients with suspected disease and no gene deletion, SMN1 copy testing with sequencing of coding regions of SMN1 copy (if present) is suggested. [38]  Molecular testing for homozygous deletion or mutation of the SMN1 gene allows efficient and specific diagnosis. [39]

The 1992 ISMAC found that the accuracy of prenatal prediction by means of chorionic villi sampling and amniocentesis was 88-99%.

Caution should be exercised when prenatal prediction is done in the presence of atypical features (see SMA variants in Physical) because these clinical variations may represent other pathogenic processes.


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