SPATACSIN mutations cause autosomal recessive juvenile amyotrophic lateral sclerosis

Abstract

The mutation of the spatacsin gene is the single most common cause of autosomal recessive hereditary spastic paraplegia with thin corpus callosum. Common clinical, pathological and genetic features between amyotrophic lateral sclerosis and hereditary spastic paraplegia motivated us to investigate 25 families with autosomal recessive juvenile amyotrophic lateral sclerosis and long-term survival for mutations in the spatascin gene. The inclusion criterion was a diagnosis of clinically definite amyotrophic lateral sclerosis according to the revised El Escorial criteria. The exclusion criterion was a diagnosis of hereditary spastic paraplegia with thin corpus callosum in line with an established protocol. Additional pathological and genetic evaluations were also performed. Surprisingly, 12 sequence alterations in the spatacsin gene (one of which is novel, IVS30 + 1 G > A) were identified in 10 unrelated pedigrees with autosomal recessive juvenile amyotrophic lateral sclerosis and long-term survival. The countries of origin of these families were Italy, Brazil, Canada, Japan and Turkey. The variants seemed to be pathogenic since they co-segregated with the disease in all pedigrees, were absent in controls and were associated with amyotrophic lateral sclerosis neuropathology in one member of one of these families for whom central nervous system tissue was available. Our study indicates that mutations in the spatascin gene could cause a much wider spectrum of clinical features than previously recognized, including autosomal recessive juvenile amyotrophic lateral sclerosis.

Figure 1

Ten ARJALS families linked to the SPG11 locus. Their origin is reported in brackets. The solid symbols refer to affected individuals as well as carriers of the SPG11 mutations; circles = females; squares = males and slashes = deceased. The code numbers of all sampled individuals (asterisks) are reported below the symbols. Colour barcodes designate haplotypes in each pedigree. Haplotypes created with markers D15S146, D15S537 and D15S123 (from top to bottom) are reported under each family member investigated. The SPG11 gene is localized between markers D15S537 and D15S123. Inferred alleles are indicated by parentheses and question marks represent alleles not able to be inferred. Key recombination events are observed between markers D15S537 and D15S123 in Patient 1810 (Family RM171) as well as among markers D15S537 and D15S123 in Patient 3011 (Family RM303).

Figure 2

(A) Family RM 257. Black symbols designate affected individuals and carriers of SPG11 mutation. White symbols symbolize unaffected subjects. Circles indicate females and squares represent males. The proband is designated with an arrow. The numbers are an internal reference for each subject. Asterisks indicate sampled individuals. (B) Electropherogram of exon/intron 30 of the SPG11 gene. The new homozygous substitution (G > A) is clearly defined in the affected individuals (Subjects 2539, 2561 and 2562) as well as the heterozygous status in the parents (Subjects 2532 and 2534) and in a sibling (Subject 2537). (C) Restriction digestion assay in the family members. Heterozygous individuals showed two bands at 600 and 500 base pairs, wild-type samples showed one band at 500 base pairs and the homozygous affected individuals remain uncleaved after digestion with EcoP15I.

Figure 3

Histopathological findings on spinal cord post-mortem samples in Patient 1737 from Family RM168. (A) Low magnification photomicrograph of the anterior horn at L1 shows a striking decrease of large motoneurons. (B) At higher magnification, several large motoneurons display central chromatolysis. (C) Most of the remaining neurons are laden with dark lipofuscin granules (pigmentary degeneration) and contain round hyaline inclusions (arrows). Klüver-Barrera staining. Bar = 800 µm (A); 100 µm (B, C).