1. Diagnostic criteria for SMA type I.

Primary criteria

Age of onset before six months and have never been able to sit independently

Genetic analysis to confirm the diagnosis, with homozygous deletion or heterozygous mutation of the SMN1 gene (5q11.2‐13.3)

Supporting criteria

Symmetrical muscle weakness of limb and trunk

Proximal muscles more affected than distal muscles and lower limbs more than upper limbs

No abnormality of sensory function

Serum creatine kinase (CK) activity not more than five times the upper limit of normal

Denervation on electrophysiological examination, and no nerve conduction velocities below 70% of the lower limit of normal. There are no abnormal sensory nerve action potentials

Muscle biopsy showing atrophic fibres of both types, hypertrophic fibres of one type (usually type I), and in chronic cases type grouping

No involvement of the central neurological systems, like hearing or vision

No involvement of non‐neurological organs

SMN1 gene ‐ survival motor neurone 1 gene
 Zerres 1999