Teepu Siddique

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.

Mutations in UBQLN2 cause dominant X-linked juvenile and adult-onset ALS and ALS/dementia

Amyotrophic lateral sclerosis (ALS) is a paralytic and usually fatal disorder caused by motor-neuron degeneration in the brain and spinal cord. Most cases of ALS are sporadic but about 5–10% are familial. Mutations in superoxide dismutase 1 (SOD1), TAR DNA-binding protein (TARDBP, also known as TDP43) and fused in sarcoma (FUS, also known as translocated in liposarcoma (TLS)) account for approximately 30% of classic familial ALS. Mutations in several other genes have also been reported as rare causes of ALS or ALS-like syndromes. The causes of the remaining cases of familial ALS and of the vast majority of sporadic ALS are unknown. Despite extensive studies of previously identified ALS-causing genes, the pathogenic mechanism underlying motor-neuron degeneration in ALS remains largely obscure. Dementia, usually of the frontotemporal lobar type, may occur in some ALS cases. It is unclear whether ALS and dementia share common aetiology and pathogenesis in ALS/dementia. Here we show that mutations in UBQLN2, which encodes the ubiquitin-like protein ubiquilin 2, cause dominantly inherited, chromosome-X-linked ALS and ALS/dementia. We describe novel ubiquilin 2 pathology in the spinal cords of ALS cases and in the brains of ALS/dementia cases with or without UBQLN2 mutations. Ubiquilin 2 is a member of the ubiquilin family, which regulates the degradation of ubiquitinated proteins. Functional analysis showed that mutations in UBQLN2 lead to an impairment of protein degradation. Therefore, our findings link abnormalities in ubiquilin 2 to defects in the protein degradation pathway, abnormal protein aggregation and neurodegeneration, indicating a common pathogenic mechanism that can be exploited for therapeutic intervention.

The gene encoding alsin, a protein with three guanine-nucleotide exchange factor domains, is mutated in a form of recessive amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) and primary lateral sclerosis (PLS) are neurodegenerative conditions that affect large motor neurons of the central nervous system. We have identified a familial juvenile PLS (JPLS) locus overlapping the previously identified ALS2 locus on chromosome 2q33. We report two deletion mutations in a new gene that are found both in individuals with ALS2 and those with JPLS, indicating that these conditions have a common genetic origin. The predicted sequence of the protein (alsin) may indicate a mechanism for motor-neuron degeneration, as it may include several cell-signaling motifs with known functions, including three associated with guanine-nucleotide exchange factors for GTPases (GEFs).

Pathological TDP‐43 distinguishes sporadic amyotrophic lateral sclerosis from amyotrophic lateral sclerosis with SOD1 mutations

Amyotrophic lateral sclerosis (ALS) is a common, fatal motor neuron disorder with no effective treatment. Approximately 10% of cases are familial ALS (FALS), and the most common genetic abnormality is superoxide dismutase‐1 (SOD1) mutations. Most ALS research in the past decade has focused on the neurotoxicity of mutant SOD1, and this knowledge has directed therapeutic strategies. We recently identified TDP‐43 as the major pathological protein in sporadic ALS. In this study, we investigated TDP‐43 in a larger series of ALS cases (n = 111), including familial cases with and without SOD1 mutations.

Presence of dendritic cells, MCP-1, and activated microglia/macrophages in amyotrophic lateral sclerosis spinal cord tissue

Dendritic cells are potent antigen‐presenting cells that initiate and amplify immune responses. To determine whether dendritic cells participate in inflammatory reactions in amyotrophic lateral sclerosis (ALS), we examined mRNA expression of dendritic cell surface markers in individual sporadic ALS (sALS), familial ALS (fALS), and nonneurological disease control (NNDC) spinal cord tissues using semiquantitative and real‐time reverse transcription polymerase chain reaction (RT‐PCR). Immature (DEC205, CD1a) and activated/mature (CD83, CD40) dendritic cell transcripts were significantly elevated in ALS tissues. The presence of immature and activated/mature dendritic cells (CD1a+ and CD83+) was confirmed immunohistochemically in ALS ventral horn and corticospinal tracts. Monocytic/macrophage/microglial transcripts (CD14, CD18, SR‐A, CD68) were increased in ALS spinal cord, and activated CD68+ cells were demonstrated in close proximity to motor neurons. mRNA expressions of the chemokine MCP‐1, which attracts monocytes and myeloid dendritic cells, and of the cytokine macrophage‐colony stimulating factor (M‐CSF) were increased in ALS tissues. The MCP‐1 protein was expressed in glia in ALS but not in control tissues and was increased in the CSF of ALS patients. Those patients who progressed most rapidly expressed significantly more dendritic transcripts than patients who progressed more slowly. These results support the involvement of immune/inflammatory responses in amplifying motor neuron degeneration in ALS.

Linkage of a gene causing familial amyotrophic lateral sclerosis to chromosome 21 and evidence of genetic-locus heterogeneity

BACKGROUND Amyotrophic lateral sclerosis is a progressive neurologic disorder that commonly results in paralysis and death. Despite more than a century of research, no cause of, cure for, or means of preventing this disorder has been found. In a minority of cases, it is familial and inherited as an autosomal dominant trait with age-dependent penetrance. In contrast to the sporadic form of amyotrophic lateral sclerosis, the familial form provides the opportunity to use molecular genetic techniques to localize an inherited defect. Furthermore, such studies have the potential to discover the basic molecular defect causing motor-neuron degeneration. METHODS AND RESULTS We evaluated 23 families with familial amyotrophic lateral sclerosis for linkage of the gene causing this disease to four DNA markers on the long arm of chromosome 21. Multipoint linkage analyses demonstrated linkage between the gene and these markers. The maximum lod score--5.03--was obtained 10 centimorgans distal (telomeric) to the DNA marker D21S58. There was a significant probability (P less than 0.0001) of genetic-locus heterogeneity in the families. CONCLUSIONS The localization of a gene causing familial amyotrophic lateral sclerosis provides a means of isolating this gene and studying its function. Insight gained from understanding the function of this gene may be applicable to the design of rational therapy for both the familial and sporadic forms of the disease.

Intense superoxide dismutase-1 immunoreactivity in intracytoplasmic hyaline inclusions of familial amyotrophic lateral sclerosis with posterior column involvement.

This report concerns retrospective immunohistochemical and immunoelectron microscopic studies on superoxide dismutase-1 (SOD1) in intracytoplasmic hyaline inclusions (IHIs) of the anterior horn cells of three patients with familial amyotrophic lateral sclerosis (ALS) with posterior column involvement. All of the patients were members of the American “C” family. Almost all of the IHIs, present in the soma and cordlike swollen neurites of some affected neurons of the three patients, were intensely stained by an antibody to human SOD1. By contrast, the cytoplasm of anterior horn cells of the ALS patients and of ten control individuals reacted only weakly with the antibody or not at all. Immunoelectron microscopy revealed that the granule-associated thick linear structures that composed the IHIs were intensely labeled by the antibody to SOD1. The IHIs were also positively stained by antibodies to ubiquitin and phosphorylated neurofilament protein, with the distribution of immunoreactivity resembling that seen with the anti-SOD1 antibody. The DNA analysis disclosed a single-site GCC to GTC substitution at codon 4 (Ala4 ± Val) in the SOD1 gene from the brain samples of the patients and from the peripheral blood of their family members. Our results suggest that SOD1 is a component of IHIs and may interact with ubiquitin and neurofilament protein, and point to the possibility that the presence of intense SOD1 immunoreactivity in the IHIs may be of relevance in processes involving structurally altered SOD1 molecules encoded by the mutated gene

Alpha subunit variants of the human glycine receptor: primary structures, functional expression and chromosomal localization of the corresponding genes.

Two cDNAs encoding variants (alpha 1 and alpha 2) of the strychnine binding subunit of the inhibitory glycine receptor (GlyR) were isolated from a human fetal brain cDNA library. The predicted amino acid sequences exhibit approximately 99% and approximately 76% identity to the previously characterized rat 48 kd polypeptide. Heterologous expression of the human alpha 1 and alpha 2 subunits in Xenopus oocytes resulted in the formation of glycine‐gated strychnine‐sensitive chloride channels, indicating that both polypeptides can form functional GlyRs. Using a panel of rodent‐human hybrid cell lines, the gene encoding alpha 2 was mapped to the short arm (Xp21.2‐p22.1) of the human X chromosome. In contrast, the alpha 1 subunit gene is autosomally located. These data indicate molecular heterogeneity of the human GlyR at the level of alpha subunit genes.

FUS-immunoreactive inclusions are a common feature in sporadic and non-SOD1 familial amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal disorder of motor neuron degeneration. Most cases of ALS are sporadic (SALS), but about 5 to 10% of ALS cases are familial (FALS). Recent studies have shown that mutations in FUS are causal in approximately 4 to 5% of FALS and some apparent SALS cases. The pathogenic mechanism of the mutant FUS‐mediated ALS and potential roles of FUS in non‐FUS ALS remain to be investigated.

Scapuloperoneal spinal muscular atrophy and CMT2C are allelic disorders caused by alterations in TRPV4

Scapuloperoneal spinal muscular atrophy (SPSMA) and hereditary motor and sensory neuropathy type IIC (HMSN IIC, also known as HMSN2C or Charcot-Marie-Tooth disease type 2C (CMT2C)) are phenotypically heterogeneous disorders involving topographically distinct nerves and muscles. We originally described a large New England family of French-Canadian origin with SPSMA and an American family of English and Scottish descent with CMT2C. We mapped SPSMA and CMT2C risk loci to 12q24.1–q24.31 with an overlapping region between the two diseases. Further analysis reduced the CMT2C risk locus to a 4-Mb region. Here we report that SPSMA and CMT2C are allelic disorders caused by mutations in the gene encoding the transient receptor potential cation channel, subfamily V, member 4 (TRPV4). Functional analysis revealed that increased calcium channel activity is a distinct property of both SPSMA- and CMT2C-causing mutant proteins. Our findings link mutations in TRPV4 to altered calcium homeostasis and peripheral neuropathies, implying a pathogenic mechanism and possible options for therapy for these disorders.