Two brothers with Pelizaeus-Merzbacher disease presenting with neonatal hypotonia and hyporeflexia are reported from the Tuft’s University School of Medicine, and Massachusetts General Hospital, Boston, and the EKS Center for Mental Retardation, Waltham, MA. Patient 1 had Apgar scores of 0 at 1 minute and 3 at 5 minutes. The neonatal exam showed signs of spinal muscular atrophy: poor suck and swallow, tongue fasciculations, reduced muscle bulk and strength, severe hypotonia, absent deep tendon reflexes, and normal sensation. An older brother had a similar disease. Parents were not related. Nystagmoid eye movements were present shortly after birth and disappeared before 1 year. Optic atrophy and dystonic arm movements developed after several months. MRI showed diffuse hypomyelination. EMG demonstrated fibrillations, high-amplitude potentials, and acute denervation. Muscle biopsy was normal. The diagnosis of Pelizaeus-Merzbacher disease was confirmed by proteolipid protein genetic studies. 
COMMENT. Pelizaeus-Merzbacher disease should be included in the differential diagnosis of limp infant syndrome and as a cause of infantile spinal muscular atrophy.