Homozygous survival motor neuron 2 gene deletion and sporadic lower motor neuron disease in children: case report and literature review.

A case of lower motor neuron disease with homozygous survival motor neuron 2 (SMN2) gene deletion is reported in this article. A 7-year-old boy was admitted to our hospital with main complaints of lower extremity weakness and difficulty squatting for the past year. SMN gene copies were quantified by multiplex ligation-dependent probe amplification. Exons 7 and 8 of the SMN1 gene were normal, but homozygous deletion of exons 7 and 8 of the SMN2 gene was identified. Homozygous deletion of exons 7 and 8 of the SMN centromeric gene was detected, and exons 7 and 8 of the SMN1 gene were found to be normal in the proband. Two copies of exons 7 and 8 of the SMN1 gene were identified, and zero copies of exons 7 and 8 of the SMN2 gene were found. We consider that this case represents a previously unrecognized type of lower motor neuron disease that resulted from homozygous deletion of the SMN2 gene.