Two infants who were asymptomatic at birth and presented at 3 and 6 months of age with acute onset generalized muscle weakness and hypotonia following respiratory infection are reported from the Schneider’s Children Hospital, New Hyde Park, NY. A suspected diagnosis of Guillain-Barre syndrome and corroborating nerve conduction studies led to a trial of immunoglobulin therapy, with minimal and questionable benefit. Subsequent DNA analyses on blood showed homozygous deletion mutation in exons 7 and 8 of the survival motor neuron (SMN) gene. The final molecular diagnosis was SMA type I. One patient died at 5 months of age of pneumonia and respiratory failure, and the other was currently surviving on a respirator. 
COMMENT. Several atypical presentations of infantile spinal muscular atrophy are cited from the literature. The acute onset of weakness and areflexia following a respiratory infection suggested a Guillain Barre syndrome, and the NCS were confirmatory. The very young age, less than 6 months, and the absent response to immunoglobulin were against this diagnosis. SMA type I was established by DNA molecular analyses. The final outcome with respiratory failure was expected.