Spinal muscular atrophy in trizygotic triplets.

The clinical, electrophysiological, pathological and genetic findings in trizygotic triplets with spinal muscular atrophy (SMA) are reported. The first child was clinically affected shortly after birth and the third one first showed symptoms at 1 month of age. Electromyography and a muscle biopsy provided evidence of lower motor neuron disease. The second child remains clinically normal, but electromyography showed fibrillation potentials and regular spontaneous motor unit activity at rest. Genetic linkage analysis revealed that the two siblings with typical type 1 SMA had the same chromosome 5q haplotype, and that the second child had a different haplotype. It is considered that in this family there is a link to SMA 5q and there is little possibility that the second child is affected. These data emphasize the need to adhere to strict clinical criteria for the diagnosis of chromosome 5q SMA.