Spinal muscular atrophy (SMA) is classified according to the age of onset and severity of the clinical manifesta tions into: acute (Werding-Hoffman disease or type I), intermediate (type II) and juvenile (Kugelberg-Wilander disease or type III) forms. All three SMAs have been linked to markers at 5q11.2-q13.3. Two candidate genes deleted in SMA patients are the survival motor neuron (SMN) gene and the neuronal apoptosis inhibitory protein (NAIP) gene. We have performed molecular analyses of these genes in 30 unrelated Macedonian families (17 with type I, eight with type II and five with type III forms of the disease). Deletions of exons 7 and 8 of the SMN gene were found in 76.6% (23/30) of patients (94.1% in type I, 87.5% in type II). Among these 23 families, 19 had both exons deleted, while four had deletions only of exon 7. Deletions of exon 5 of the NAIP gene were found in 41.2% (7/17) patients with type I SMA and in 12.5% (1/8) of patients with type II SMA. No deletions of the SMN gene were found in 30 parents and 30 normal controls. We found 2/30 (6.7%) parents to be homozygous for the dele tion of exon 5. Our data support the hypothesis that the telomeric SMN gene plays a major role in determining the clinical course of the disease, while the defects in the NAIP gene have only a modifying effect on the phenotype.

Key words: Spinal muscular atrophy (SMA); Survival motor neuron (SMN) gene; Neuronal apoptosis inhibitory protein (NAIP) gene