Which clinical history findings are characteristic of spinal muscular atrophy (SMA) type I (Werdnig-Hoffmann disease)?

Updated: Apr 28, 2014
  • Author: Hidehiro Takei, MD; Chief Editor: Adekunle M Adesina, MD, PhD  more...
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Type I SMA (Werdnig-Hoffmann disease)

Type I SMA is the most severe form. Patients present with profound hypotonia and generalized weakness (“floppy infants”) and never achieve the ability to sit. By definition, all patients present before age 6 months (sometimes with onset in the prenatal period). The diaphragm and the extraocular muscles tend to be spared (in contrast to SMA-plus disease types and severe congenital SMA). [30] No cardiac muscle involvement is seen. Creatine kinase is normal.

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