Betsy A. Hosler

Mutations in the FUS/TLS gene on chromosome 16 cause familial amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal degenerative motor neuron disorder. Ten percent of cases are inherited; most involve unidentified genes. We report here 13 mutations in the fused in sarcoma/translated in liposarcoma (FUS/TLS) gene on chromosome 16 that were specific for familial ALS. The FUS/TLS protein binds to RNA, functions in diverse processes, and is normally located predominantly in the nucleus. In contrast, the mutant forms of FUS/TLS accumulated in the cytoplasm of neurons, a pathology that is similar to that of the gene TAR DNA-binding protein 43 (TDP43), whose mutations also cause ALS. Neuronal cytoplasmic protein aggregation and defective RNA metabolism thus appear to be common pathogenic mechanisms involved in ALS and possibly in other neurodegenerative disorders.

A gene encoding a putative GTPase regulator is mutated in familial amyotrophic lateral sclerosis 2

Amyotrophic lateral sclerosis 2 (ALS2) is an autosomal recessive form of juvenile ALS and has been mapped to human chromosome 2q33. Here we report the identification of two independent deletion mutations linked to ALS2 in the coding exons of the new gene ALS2. These deletion mutations result in frameshifts that generate premature stop codons. ALS2 is expressed in various tissues and cells, including neurons throughout the brain and spinal cord, and encodes a protein containing multiple domains that have homology to RanGEF as well as RhoGEF. Deletion mutations are predicted to cause a loss of protein function, providing strong evidence that ALS2 is the causative gene underlying this form of ALS.

A locus on chromosome 9p confers susceptibility to ALS and frontotemporal dementia.

Objective: To perform genetic linkage analysis in a family affected with ALS and frontotemporal dementia (FTD). Methods: The authors performed a genome-wide linkage analysis of a four-generation, 50-member Scandinavian family in which five individuals were diagnosed with ALS and nine with FTD. Linkage calculations assuming autosomal dominant inheritance of a single neurodegenerative disease manifesting as either ALS or FTD with age-dependent penetrance were performed. Further analyses for ALS alone and FTD alone were performed. A parametric logarithm of odds (lod) score of 2.0 or greater was required for further study of a potential locus and crossover (haplotype) analysis. Results: A new ALS-FTD locus was identified between markers D9s1870 and D9s1791 on human chromosome 9p21.3-p13.3. A maximum multipoint lod score of 3.00 was obtained between markers D9s1121 and D9s2154. Crossover analysis indicates this region covers approximately 21.8 cM, or 14Mb. Conclusions: A locus on chromosome 9p21.3-p13.3 is linked to ALS-FTD.

Reduced expression of the Kinesin-Associated Protein 3 (KIFAP3) gene increases survival in sporadic amyotrophic lateral sclerosis.

Amyotrophic lateral sclerosis is a degenerative disorder of motor neurons that typically develops in the 6th decade and is uniformly fatal, usually within 5 years. To identify genetic variants associated with susceptibility and phenotypes in sporadic ALS, we performed a genome-wide SNP analysis in sporadic ALS cases and controls. A total of 288,357 SNPs were screened in a set of 1,821 sporadic ALS cases and 2,258 controls from the U.S. and Europe. Survival analysis was performed using 1,014 deceased sporadic cases. Top results for susceptibility were further screened in an independent sample set of 538 ALS cases and 556 controls. SNP rs1541160 within the KIFAP3 gene (encoding a kinesin-associated protein) yielded a genome-wide significant result (P = 1.84 × 10−8) that withstood Bonferroni correction for association with survival. Homozygosity for the favorable allele (CC) conferred a 14.0 months survival advantage. Sequence, genotypic and functional analyses revealed that there is linkage disequilibrium between rs1541160 and SNP rs522444 within the KIFAP3 promoter and that the favorable alleles of rs1541160 and rs522444 correlate with reduced KIFAP3 expression. No SNPs were associated with risk of sporadic ALS, site of onset, or age of onset. We have identified a variant within the KIFAP3 gene that is associated with decreased KIFAP3 expression and increased survival in sporadic ALS. These findings support the view that genetic factors modify phenotypes in this disease and that cellular motor proteins are determinants of motor neuron viability.

Identification of two novel loci for dominantly inherited familial amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a rapidly progressive, adult-onset motor neuron disease that arises as a dominantly inherited trait in approximately 10% of ALS cases. Mutations in one gene, cytosolic Cu/Zn superoxide dismutase (SOD1), account for approximately 25% of familial ALS (FALS) cases. We have performed a genetic linkage screen in 16 pedigrees with FALS with no evidence for mutations in the SOD1 gene and have identified novel ALS loci on chromosomes 16 and 20. The analysis of these genes will delineate pathways implicated as determinants of motor-neuron viability and provide insights into possible therapies for ALS.

Identification of three novel mutations in the gene for Cu/Zn superoxide dismutase in patients with familial amyotrophic lateral sclerosis.

Abstract About 10% of cases of amyotrophic lateral sclerosis (ALS), a paralytic disorder characterized by death of motor neurons in the brain and spinal cord, exhibit autosomal dominant inheritance. A subgroup of these familial cases are caused by mutations in the gene encoding Cu Zn superoxide dismutase (SOD1). We report here three additional mutations occurring in the SOD1 gene in three families with ALS. Two of these changes are missense mutations in exon 5 of the SOD1 gene, resulting in leucine 144 to serine and alanine 145 to threonine substitutions. The third, a single base pair change in intron 4 immediately upstream of exon 5, results in an alternatively spliced mRNA. The alternate transcript conserves the open reading frame of exon 5, producing an SOD1 protein with three amino acids inserted between exons 4 and 5 (following residue 118). These three mutations bring to 29 the total number of distinct SOD1 mutations associated with familial ALS.

Three novel mutations and two variants in the gene for Cu/Zn superoxide dismutase in familial amyotrophic lateral sclerosis

Autosomal dominant inheritance is exhibited by about 10% of cases of amyotrophic lateral sclerosis (ALS), a paralytic disorder characterized by the death of motor neurons in the brain and spinal cord. A subgroup of these familial cases are linked to mutations in the gene which codes for Cu/Zn superoxide dismutase (SOD1). We report three additional mutations occurring in the SOD1 gene in ALS patients and two single base pair variant changes. The single base pair change in an ALS family causes a glycine 93 to valine substitution, which is the fifth distinct amino acid change reported for the glycine 93 residue. One missense mutation in exon 5 would substitute neutral valine for the negatively-charged aspartate 124 (aspartate 124 to valine). An individual with an apparently sporadic case of ALS carries a three base pair deletion in exon 5 of the SOD1 gene. These three mutations bring to 38 the total number of distinct SOD1 mutations associated with familial ALS.

Survival motor neuron protein in the nucleolus of mammalian neurons.

Spinal muscular atrophy (SMA) is an inherited motor neuron disease caused by mutations in the survival motor neuron gene (SMN1). While it has been shown that the SMN protein is involved in spliceosome biogenesis and pre-mRNA splicing, there is increasing evidence indicating that SMN may also perform important functions in the nucleolus. We demonstrate here through the use of a previously characterized polyclonal anti-SMN antibody, abSMN, that the SMN protein shows a striking colocalization with the nucleolar protein, fibrillarin, in both nucleoli and Cajal bodies/gems of primary neurons. Immunoblot analysis with antifibrillarin and two different anti-SMN antibodies reveals that SMN and fibrillarin also cofractionate in the insoluble protein fraction of cultured cell lysates. Immunoprecipitation experiments using whole cell extracts of HeLa cells and cultured neurons revealed that abSMN coprecipitated small amounts of the U3 small nucleolar RNA (snoRNA) previously shown to be associated with fibrillarin in vivo. These studies raise the possibility that SMN may serve a function in rRNA maturation/ribosome synthesis similar to its role in spliceosome biogenesis.

Confirmation of linkage of type 1 hereditary sensory neuropathy to human chromosome 9q22

Objectives: 1) To confirm linkage of hereditary sensory neuropathy type 1 (HSN-I) to human chromosome 9q22 in a large American family of German origin. 2) To construct a yeast artificial chromosome (YAC) contig spanning the HSN-I candidate interval. 3) To investigate the HSN-I contig for potential candidate genes. Background: HSN-I is a rare peripheral neuropathy characterized by loss of temperature sensation, ulceration and osteomyelitis of the digits, and subtle distal weakness. A gene for HSN-I has previously been mapped to human chromosome 9q22.1-q22.3 between markers D9S318 and D9S176 in an 8-cM interval in four Australian families. Methods: In a large German-American family with HSN-I, genome-wide linkage analysis was performed on 68 family members extending over five generations and including 17 affected members. Genotyping was performed with PCR, and the resulting genotypes were analyzed with two-point linkage analysis with Fastlink. A YAC contig was constructed based on the Whitehead Institute YAC contig WC9.3. Results: Two-point linkage analysis resulted in a maximum lod score of 8.2 at θ = 0 for marker D9S1815. Haplotype analysis locates the HSN-I gene between markers D9S1797 and D9S197. Using YAC clones from the Centre d’Etude du Polymorphism Humain YAC Library, we constructed a YAC contig spanning these markers. Based on the radiation hybrid map of the human genome, we estimate that the size of this interval is less than 2,500 kb. Conclusions: Our study confirms linkage of a putative HSN-I gene to chromosome 9q22, considerably narrows the HSN-I locus, and provides a basis for identification of the HSN-I gene.

Refined mapping and characterization of the recessive familial amyotrophic lateral sclerosis locus (ALS2) on chromosome 2q33

ABSTRACT Amyotrophic lateral sclerosis (ALS) is a progressive degenerative neuromuscular disease that shows familial, autosomal dominant inheritance in 10%–15% of cases. Previous genetic analysis of one large family linked a recessive form of familial ALS (FALS-AR type 3) to the chromosome 2q33–35 region. Using additional polymorphic markers, we have narrowed the size of the linked region to approximately 1.7 cM by linkage and haplotype analysis. We have also established a yeast artificial chromosome contig across the locus that covers an approximate physical distance of 3 million bases. Based on this contig, genes and expressed sequences that map near the 2q33 region have been examined to determine whether they are located within this ALS2 candidate locus. Five identified genes and 34 expressed sequence tags map within the region defined by crossover analysis and merit further consideration as candidate genes for this disease.