Brazilian family with pure autosomal dominant spastic paraplegia maps to 8q: Analysis of muscle beta 1 syntrophin

The autosomal dominant hereditary spastic paraplegias (AD‐HSP) are a heterogeneous group of degenerative disorders of the central motor system, characterized by progressive spasticity of the lower limbs. Five loci for pure AD‐HSP have been identified to date: SPG3 at 14q, SPG4 at 2p, SPG6 at 15q, SPG8 at 8q, and more recently SPG10 at 12q. We have analyzed a Brazilian family with 16 affected individuals by pure AD‐HSP who developed progressive gait disturbance with onset at age 18–26 years. Linkage analysis performed with 13 relatives (6 affected and 7 normal) excluded SPG3, SPG4, and SPG6 as candidate regions. However, positive LOD scores were obtained with markers flanking the candidate region for the SPG8 locus [maximum two point Lod score (Zmax) = 3.3 at theta = 0 for D8S1804]. In this region lies the syntrophin beta 1 gene (SNT2B1), a widely expressed dystrophin‐associated protein and therefore a good positional and functional candidate for this disease. Immunohistochemical and Western Blot (WB) studies showed that the distribution, expression, and apparent molecular weight of the beta 1 syntrophin protein were comparable to those of normal control individuals. Therefore, it is unlikely that defects in this protein are related to SPG8, at least in the present family. Am. J. Med. Genet. 92:122–127, 2000. © 2000 Wiley‐Liss, Inc.