X-linked spinal muscular atrophy 2 (SMAX2) is a form of spinal muscular atrophy

Spinal muscular atrophy

Spinal Muscular Atrophy is a neuromuscular disease characterized by degeneration of motor neurons, resulting in progressive muscular atrophy and weakness. The clinical spectrum of SMA ranges from early infant death to normal adult life with only mild weakness...

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It is similar to but distinguishable from Werdnig-Hoffmann disease. Typically it manifests at or before birth, which is unusual for SMN-SMA, and it only affects boys, where SMN-SMA affects both sexes equally.

The "2" is used to distinguish the condition from Kennedy disease

Kennedy disease

Kennedy's disease or X-linked Spinal and Bulbar Muscular Atrophy or Spinobulbar Muscular Atrophy or X-Linked Bulbo-Spinal Atrophy is an X-linked recessive, slow progressing, neurodegenerative disease associated with mutation of the androgen receptor...

. However, the "2" is not always used. In this context, the condition may simply be abbreviated "XL-SMA".

It is associated with UBE1

UBE1

Ubiquitin-like modifier activating enzyme 1, also known as UBA1, is an enzyme which in humans is encoded by the UBA1 gene.- Function :...

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