Autosomal recessive spastic paraplegias types 7 and 76

Introduction. Since 2017, the Research Centre for Medical Genetics has been conducting the first clinical and molecular study in Russia of a heterogeneous spastic paraplegia group based on the MPS high throughput sequencing method. Our group of molecularly diagnosed SPGs (types with known genes) includes 122 families with 22 SPG types. This article continues the publication series on the study results. The study aimed to determine the proportion and analyze the clinical, molecular, and genetic characteristics of two autosomal recessive forms, SPG7 and SPG76, in a group of identified SPGs. Materials and methods. We assessed three non-inbred Russian families: two with SPG7 (a non-familial and a familial case) and one with SPG76 (a non-familial cases). Molecular genetic methods included massive parallel sequencing (MPS) panel for spastic paraplegia, Sanger sequencing, and multiplex ligation-dependent probe amplification (MLPA)). Results. SPG7 was detected in 2 families and accounted for 1.6% of the entire SPG group and 8.7% of the autosomal recessive subgroup (less than in several other studies). The compound heterozygous genotypes in both families included the most frequent mutation in the SPG7 gene, c.1529CT (p.Ala510Val); the allelic mutation in one case was a 4-exon deletion not previously described, while the other was a known mutation, c.228TC (p.Ile743Thr). Despite a similar age at onset (end of the 3rd4th decade), the symptoms were different: uncomplicated spastic paraplegia in the non-familial case, while in the affected brothers prevailed ataxia; in both families, brain MRI showed cerebellar atrophy. The SPG76 case is a rare one, especially in a non-inbred family, and the first in Eastern Europe. A total of 28 families, mostly inbred, have been described worldwide. Two new mutations were found in the CAPN1 gene in the compound heterozygous state: c.398_399insAGTGGTTCCGCCGGCC (p. Arg133Glnfs*39) and c.1535GA (p.Arg512His). Clinical features of the 30-year-old patient were typical, with onset at 20 years of age, spastic paraplegia and ataxia, and without brain MRI abnormalities. Conclusion. The range of autosomal recessive SPGs in Russian patients includes both common and very rare forms occurring in non-inbred families. Of the 5 mutations found in the SPG7 and CAPN1 genes, 3 have not been previously described. Our observations demonstrate the close relationship between spastic paraplegia and ataxia and the significance of MPS and MLPA technologies in the diagnostics of SPG.