Table 1.

Diagnostic criteria proposed by Pitt et al. to distinguish SMARD1 from other similar conditions and to facilitate the classification of the disease [81]

Clinical criteria	Histopathological criteria	EMG criteria
Low birth weight (< 3rd percentile)	Reduced myelinated fiber diameter in sural nerve biopsiesa	Evidence of acute or chronic distal denervation
Onset of symptoms within the first 3 months of life	Slight evidence of progressive myelinated fiber degeneration in biopsies taken up to 3–4 months of age	Evidence of significant slowing (< 70% of LLN) in one or more motor a/o sensory nerves
Unilateral or bilateral diaphragmatic weakness	No evidence of regeneration or demyelination that can justify the reduction in fiber size
Ventilator dependence within < 1 month of onset associated with an inability to wean
No evidence of other dysmorphology or other conditions

LLN lower limit of normal range

^aSince the thickness of the myelin sheath is appropriate for the axon size, its reduction in diameter originates from the axon, the size of which is similarly reduced