SMN2-deletion in childhood-onset spinal muscular atrophy.
The human genome has two homologous survival motor neuron genes, SMN1 and SMN2. Although deletions of SMN1 are frequently reported in childhood-onset spinal muscular atrophy (SMA), SMN2 have been found to be intact in patients with the disorder. We report on a 5-year-old boy with childhood-onset SMA who has a homozygous deletion of SMN2. He had wasting, weakness, and hyporeflexia, predominantly in the distal muscles. The muscles involved showed chronic neurogenic changes on electromyogram. There was no sensory involvement. A nerve conduction study showed near normal conduction velocity with reduction in the amplitude of the compound muscle action potential. Analysis of polymerase chain reaction-restriction fragment length polymorphism as well as single-strand conformation polymorphism on exons 7 and 8 of the SMN genes revealed the SMN2-deletion. Base sequencing and densitometric analysis of the critical region (exon 7) did not show any microdeletion or duplication of SMN1, but confirmed the deletion of SMN2. We conclude that a deletion of SMN2 may also result in the SMA phenotype.
Srivastava
S
S
Department of Medical Genetics, Sanjay Gandhi Postgraduate Institute of Medical Sciences, Lucknow, India.
Mukherjee
M
M
Panigrahi
I
I
Shanker Pandey
G
G
Pradhan
S
S
Mittal
B
B
D002648:Child; D017362:Cyclic AMP Response Element-Binding Protein; D004247:DNA / Q000235:genetics; D005192:Family Health; D017353:Gene Deletion; D006801:Humans; D008297:Male; D009134:Muscular Atrophy, Spinal / Q000235:genetics* / Q000473:pathology; D009419:Nerve Tissue Proteins / Q000235:genetics*; D010375:Pedigree; D012150:Polymorphism, Restriction Fragment Length; D016601:RNA-Binding Proteins; D055532:SMN Complex Proteins; D055533:Survival of Motor Neuron 1 Protein; D055540:Survival of Motor Neuron 2 Protein
D017362:Cyclic AMP Response Element-Binding Protein; D009419:Nerve Tissue Proteins; D016601:RNA-Binding Proteins; D055532:SMN Complex Proteins; C526471:SMN1 protein, human; C526477:SMN2 protein, human; D055533:Survival of Motor Neuron 1 Protein; D055540:Survival of Motor Neuron 2 Protein; D004247:DNA