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A previously healthy girl died suddenly and unexpectedly at three months of age in her sleep and an autopsy failed to reveal an adequate cause of death. As the father was known to have myophosphorylase (PPL) deficiency (McArdle's disease), we performed molecular genetic analysis of the PPL gene in autopsy muscle of the proposita. The girl was homozygous for the nonsense mutation at codon 49 most commonly associated with typical McArdle's disease. This report suggests that among children presenting as Sudden Infant Death Syndrome (SIDS) there may be cases associated with myophosphorylase deficiency.

We describe two unrelated Spanish families with isolated sensorineural hearing loss. In both pedigrees, the deafness was transmitted maternally, which suggested a mitochondrial, DNA (mtDNA) defect. Within the same pedigree, some relatives showed aminoglycoside-induced deafness, whereas others were not exposed to aminoglycosides before the onset of hearing loss. Molecular genetic analysis in both families showed the A-to-G transition at nt 1555 (A1555G) in the mitochondrial 12S rRNA gene. In one pedigree, the mutation was homoplasmic; in the other, it was heteroplasmic. To assess the frequency of this mutation, we screened 42 patients of various ethnic backgrounds with isolated sensorineural hearing loss; none harbored the A1555G mutation. This is the first report of heteroplasmy in a family with isolated sensorineural deafness associated with the A1555G mutation.