CRAMPS AND MINIMAL EMG ABNORMALITIES AS PRECLINICAL MANIFESTATIONS OFSPINAL MUSCULAR-ATROPHY PATIENTS WITH HOMOZYGOUS DELETIONS OF THE SMNGENE

The characterization of deletions in the SMN gene provides a helpful t ool to confirm the diagnosis of spinal muscular atrophy (SMA). However , there may be homozygous deletions of the SMN gene in some unaffected siblings of SMA type IT and III patients. We present two SMA families with affected siblings demonstrating a homozygous deletion of the SMN gene with extremely different phenotypes. We propose a preclinical ca tegory of an SMA patient with homozygous deletion of the SMN gene: tho se with minimal expression of the disease including cramps and EMG abn ormalities that may develop the complete SMA phenotype in the future.