Linkage of recessive familial amyotrophic lateral sclerosis to chromosome 2q33-q35

Inheritance of frontotemporal dementia

BACKGROUND

Previous studies of families with fronto-temporal dementia (FTD) support an autosomal dominant inheritance pattern, but most studies have described genetic transmission in individual families specifically selected for the presence of multiple affected individuals.

OBJECTIVE

To investigate the familial presentation and inheritance of FTD and related disorders among a large group of FTD index cases unselected for family history of dementia.

DESIGN AND SETTING

We interviewed family members and reviewed medical records and autopsy reports at a university hospital and a university-affiliated hospital to determine the frequency of familial FTD and the most likely mode of inheritance. Characteristic families with the disorder are described, along with the history, clinical findings, and neuroimaging results in affected members of these families.

PATIENTS AND PARTICIPANTS

The 42 index cases of FTD had a mean age of onset of 56.1 years (range, 40-69 years). Of these patients, 21 (50%) were women. All but one of the patients were white. Participants included male and female spouses and children of the index cases. family member with an FTD spectrum disorder and were considered familial cases. The majority (17 [89%]) of familial FTD cases showed a pattern consistent with dominant inheritance. If depression is excluded, familial cases decrease from 19 (45%) to 17 (40%), of which 15 (88%) showed a dominant transmission pattern. The initial presentations in the nonindex familial cases varied but most frequently consisted of personality and behavioral changes that preceded cognitive impairment (19 [43%]), followed by psychiatric illness (14 [33%]), dementia without behavioral change (5 [11%]), amyotrophic lateral sclerosis (5 [11%]), and parkinsonism (2[5%]). Two of the affected nonindex cases had dual presenting diagnoses. The average age of onset was 56.1 years and did not differ significantly between familial and nonfamilial cases. Onset of FTD-related symptoms occurred after the age of 65 years in only 4(10%) of 42 index cases and 3 (5%) of 60 affected relatives.

CONCLUSIONS

Familial FTD is usually inherited in an autosomal dominant pattern. The initial onset is insidious, often consisting of mood and behavioral changes occurring in presenile years that are often erroneously attributed to other nonneurologic causes. Although the precise incidence of FTD in North America is not known, it is one of the most common presenile dementias.

A yeast artificial chromosome-based physical map of the juvenile amyotrophic lateral sclerosis (ALS2) critical region on human chromosome 2q33-q34

The autosomal recessive form of juvenile amyotrophic lateral sclerosis (ALS2; RFALS Type 3) has previously been mapped to the 8-cM interval flanked by D2S115 and D2S155 on human chromosome 2q33-q34. We have established a yeast artificial chromosome (YAC) contig spanning an approximately 8-Mb region of the ALS2 candidate region and mapped 52 transcribed DNA sequences including 13 known genes and 39 expressed sequenced tags within this YAC contig. The establishment of a YAC contig and transcript map that spans the region containing the ALS2 mutation is an essential step in the identification of the ALS2 gene.

Identification of the mouse neuromuscular degeneration gene and mapping of a second site suppressor allele

The nmd mouse mutation causes progressive degeneration of spinal motor neurons and muscle atrophy. We identified the mutated gene as the putative transcriptional activator and ATPase/DNA helicase previously described as Smbp2, Rip1, Gf1, or Catf1. Mutations were found in two alleles-a single amino acid deletion in nmdJ and a splice donor mutation in nmd2J. The selective vulnerability of motor neurons is striking in view of the widespread expression of this gene, although the pattern of degeneration may reflect a specific threshold since neither allele is null. In addition, the severity of the nmd phenotype is attenuated in a semidominant fashion by a major genetic locus on chromosome (Chr) 13. The identification of the nmd gene and mapping of a major suppressor provide new opportunities for understanding mechanisms of motor neuron degeneration.

The genetic and molecular mechanisms of motor neuron disease

Significant progress has been made in the identification of genes and chromosomal loci associated with several types of motor neuron disease. Of particular interest is recent work on the pathogenic mechanisms underlying these diseases, especially studies in in vitro model systems and in transgenic and gene-targeted mice.

Serpin=serine protease-like complexes within neurofilament conglomerates of motoneurons in amyotrophic lateral sclerosis

Neurofilamentous conglomerates (NfCg), as axonal spheroids or conglomerates in motoneurons, are the histopathologic hallmarks for early stages of amyotrophic lateral sclerosis (ALS). We hypothesize that NfCg may be formed by post-translational modifications of altered Nf proteins that include: (1) hyperphosphorylation, (2) glycosylation (or glycoxidation), (3) nitration, (4) ubiquitination and/or (5) crosslinking by the Ca++-dependent transglutaminase (TGase). These, as well as other changes, are predicted to be initiated or accentuated by oxidative damage. The damaged Nf proteins then activate cascades of intracellular protein degradation which include ATP-dependent ubiquitin/proteasome proteolysis. Other proteolytic systems, either Ca++-dependent or independent, may also be activated, such as serine and cysteine protease systems. These enzymes, either lysosomal or non-lysosomal may also participate in the degradation of damaged Nf proteins being balanced by their cognate inhibitors. Protein complexes formed by these protease=inhibitor systems, along with damaged Nf proteins, may accumulate within the cell bodies as neuronal inclusions, since a number of intracellular inclusions are found in motor neurons in ALS. In the current study, we investigated the involvement of serine proteases and their serpins in NfCg formation. Pairs of three serine proteases (trypsin, chymotrypsin and thrombin) and their cognate serpins (alpha1-anti-trypsin, alpha1-anti-chymotrypsin, and protease nexin I) were probed in motoneurons with their antibodies for both NfCg and inclusions. Positive immunoreactivities for all serine proteases and their cognate serpins support the contention that the imbalance of serine proteases and internalized serpins may have a role in formation of NfCg and inclusions, and hence, the pathogenesis of ALS.

Identification of six novel SOD1 gene mutations in familial amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease characterized by the premature death of motor neurons. In approximately 10% of the cases the disease is inherited as autosomal dominant trait (FALS). It has been found that mutations in the Cu/Zn superoxide dismutase gene (SOD1) are responsible for approximately 15% of FALS kindreds. We screened affected individuals from 70 unrelated FALS kindreds and identified 10 mutations, 6 of which are novel. Surprisingly, we have found a mutation in exon 3, which includes most of the active site loop and Zn2+ binding sites, a region where no previous SOD1 mutations have been found. Our data increase the number of different SOD1 mutations causing FALS to 55, a significant fraction of the 154 amino acids of this relatively small protein.

Isolation and characterization of the human aldehyde oxidase gene: conservation of intron/exon boundaries with the xanthine oxidoreductase gene indicates a common origin

Aldehyde oxidase (AO) is a molybdo-flavo enzyme involved in the metabolism of various endogenous and exogenous N-heterocyclic compounds of pharmacological and toxicological importance. The enzyme is the product of a gene which is implicated in the aetio-pathogenesis of familial recessive amyotrophic lateral sclerosis. Here, we report the cloning and structural characterization of the human AO gene. AO is a single copy gene approximately 85 kb long with 35 transcribed exons. The transcription-initiation site and the sequence of the 5'-flanking region, containing several putative regulatory elements, were determined. The 5'-flanking region contains a functional promoter, as assessed by appropriate reporter constructs in transient transfection experiments. Comparison of the AO gene structure shows conservation of the position and type of exon/intron junctions relative to those observed in the gene coding for another molybdo-flavoprotein, i.e. xanthine oxidoreductase (XOR). As the two genes code for proteins with a high level of amino acid identity, our results strongly suggest that the AO and XOR genetic loci arose as the consequence of a duplication event. Southern blot analysis conducted on genomic DNA from various animal species with specific cDNA probes indicates that the AO gene is less conserved than the XOR gene during evolution.

Linkage of the gene for an autosomal dominant form of juvenile amyotrophic lateral sclerosis to chromosome 9q34

We performed genetic mapping studies of an 11-generation pedigree with an autosomal dominant, juvenile-onset motor-systems disease. The disorder is characterized by slow progression, distal limb amyotrophy, and pyramidal tract signs associated with severe loss of motor neurons in the brain stem and spinal cord. The gene for this disorder, classified as a form of juvenile amyotrophic lateral sclerosis (ALS), is designated "ALS4." We performed a genomewide search and detected strong evidence for linkage of the ALS4 locus to markers from chromosome 9q34. The highest LOD score (Z) was obtained with D9S1847 (Z=18.8, recombination fraction of .00). An analysis of recombinant events identified D9S1831 and D9S164 as flanking markers, on chromosome 9q34, that define an approximately 5-cM interval that harbors the ALS4 gene. These results extend the degree of heterogeneity within familial ALS syndromes, and they implicate a gene on chromosome 9q34 as critical for motor-neuron function.

Nab1, a corepressor of NGFI-A (Egr-1), contains an active transcriptional repression domain

Nab proteins constitute an evolutionarily conserved family of corepressors that specifically interact with and repress transcription mediated by three members of the NGFI-A (Egr-1, Krox24, zif/268) family of immediate-early gene transcription factors, which includes NGFI-C, Krox20, and Egr3. We explored the mechanism of Nab1 repression and identified structural domains required for Nab1 function. Nab1 does not act by blocking DNA binding or nuclear localization of NGFI-A. In fact, Nab1 repression is not unique to NGFI-A because multiple types of non-NGFI-A activation domains were repressed, as was a heterologous transcription factor carrying the NGFI-A R1 domain, which is required for Nab1 interaction. Additionally, Nab1 tethered directly to DNA repressed constitutively active promoters. Tethered repression was not dependent on the identity of the basal promoter elements, the presence of a distal enhancer, or the distance separating the binding sites from the promoter. These results suggest that Nab1 repression is not specific to particular activators and that Nab1 is an active repressor that works by a direct mechanism. We identified a bipartite-like nuclear localization sequence and localized the repression function to the Nab conserved domain 2 (NCD2), a region found in the carboxy-terminal half of all Nab proteins. Three small regions of homology between Nab1 and previously characterized corepressors, Dr1 and E1b 55-kDa protein, were identified within NCD2. Replacement mutagenesis of residues conserved between these proteins interfered with Nab1 repression, although Nab1 does not function by the same mechanism as Dr1. The human NAB1 genomic locus was mapped to chromosome 2q32.3-33.

Therapeutic advances in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a progressive and rapidly fatal neurodegenerative disease in which both upper and lower motoneurones are involved. The recent discovery of mutations affecting the superoxide dismutase (SOD) gene has given impetus to research on the role of oxidative stress in the pathogenesis of familial ALS, while further evidence for a role of excitotoxicity in the disease process has arisen. In this review, Erik Louvel, Jacques Hugon and Adam Doble discuss these findings and, in addition, describe how a number of large, well-controlled clinical trials have taken place to test potential therapies suggested by different aetiological hypotheses, including immunosuppressive therapies, neurotrophic factors, antioxidants and anti-excitotoxic drugs. These trials have led to the first modest steps in the treatment of this devastating neurological disease.

Epidemiology of mutations in superoxide dismutase in amyotrophic lateral sclerosis

We registered 366 families in a study of dominantly inherited amyotrophic lateral sclerosis. Two hundred ninety families were screened for mutations in the gene encoding copper-zinc cytosolic superoxide dismutase (SOD1). Mutations were detected in 68 families. The most common SOD1 mutation is an alanine for valine substitution in codon 4 (50%). We present clinical and genetic data concerning 112 families with 395 affected individuals. The clinical characteristics of patients with familial amyotrophic lateral sclerosis arising from SOD1 mutations are similar to those lacking SOD1 defects. Mean age at onset was earlier (Wilcoxon test, p = 0.004) in the SOD1 group (46.9 years [standard deviation, 12.5] vs 50.5 years [11.5] in the non-SOD1 group). Bulbar onset was associated with a later onset age. The presence of either of two mutations, G37R and L38V, predicted an earlier age at onset. Kaplan-Meier plots demonstrated shorter survival in the SOD1 group compared with the non-SOD1 group at early survival times (Wilcoxon test, p = 0.0007). The presence of one mutation, A4V, correlated with shorter survival. G37R, G41D, and G93C mutations predicted longer survival. This information suggests it will be productive to investigate other genetic determinants in amyotrophic lateral sclerosis and to use epidemiological characteristics of the disease to help discern molecular mechanisms of motor neuron cell death.

The relationship of spinal muscular atrophy to motor neuron disease: investigation of SMN and NAIP gene deletions in sporadic and familial ALS

Amyotrophic lateral sclerosis (ALS) is found in a familial form in around 5-10% of cases. Of these familial cases around 20% are associated with mutations of SOD-1. The genetic basis of the disease in the remaining familial cases, and genetic risk factors in sporadic cases, are unknown. Recently, the common forms of spinal muscular atrophy (SMA) have been associated with mutations of the SMN and NAIP genes on chromosome 5, in the region q11.2-13.3. Some patients with both familial and sporadic motor neuron disease show only lower motor neuron signs, in common with SMA patients, and families containing individuals with phenotypes of both childhood SMA and adult motor neuron disease have been reported. We therefore examined the SMA locus as a candidate for ALS, in 54 patients with sporadic motor neuron disease, and 10 single-generation familial patients (with no evidence of SOD-1 mutations), and in a single patient with Brown-Vialetto-Van Laere syndrome. No mutations of the SMN or NAIP genes were detected. The difficulties of classification of lower motor neuron presentations of motor neuron diseases are discussed. The demonstration that mutations diagnostic of SMA are not found in ALS patients helps distinguish these conditions.

Familial amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis is sporadic in ninety percent of cases and familial (FALS) in ten percent. Both forms of FALS whether transmitted as an autosomal dominant (DFALS) or as an autosomal recessive (RFALS) trait is genetically heterogeneous. The locus for one form of RFALS maps to chromosome 2q33. Fifteen percent of DFALS families have mutations in the gene for Cu, Zn superoxide dismutase (SOD1) gene which is coded on chromosome 21. These mutations result in decreased SOD1 activity and shortened half-life of the protein in most instances. Transgenic mice overexpressing mutated SOD1 protein develop an ALS-like disease which suggests that the degeneration of motor neurons in DFALS is caused by the gain of a novel toxic function by mutated SOD1 rather than by the decrease of SOD1 activity. Possible mechanisms of the novel neurotoxic function of mutated SOD1 are discussed.

Genetics of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a paralytic disorder caused by degeneration of motor neurons in the brain and spinal cord. Identification of mutations in the gene for Cu,Zn superoxide dismutase (SOD1) in a subset of ALS families made it possible to develop a transgenic mouse model of ALS and to investigate its pathogenesis. These investigations suggest that mutant SOD1 acts through a toxic gain of function which may involve generation of free radicals. Conformational change in the mutant SOD1 protein, especially the distortion of the 'rim' of the electrostatic guidance channel may be central to this toxic gain of function and to the pathogenesis of ALS.

Autosomal recessive paraparesis with amyotrophy of hands and feet and white matter lesions

We report two siblings with a hitherto undescribed syndrome of autosomal recessive spastic paraparesis accompanied by amyotrophy of hands and feet, and mental deterioration. Laboratory tests showed signs of lower motoneuron involvement in the four limbs, more accentuated in the distal regions. Brain MR showed bilateral symmetrical white matter lesions. We discuss the nosological status of this syndrome in relation to other similar forms of "complicated" spastic paraparesis.

Prevention of activity-dependent neuronal death: vasoactive intestinal polypeptide stimulates astrocytes to secrete the thrombin-inhibiting neurotrophic serpin, protease nexin I

Neuronal cell death occurs as a programmed, naturally occurring mechanism and is the primary regressive event in central nervous system development. Death of neurons also occurs on an injury-induced basis after trauma and in human neurodegenerative diseases. Classical neurotrophic factors can reverse this phenomenon in experimental models prompting initiation of clinical trials in conditions such as amyotrophic lateral sclerosis and Alzheimer's disease. The glial-derived protease nexin I (PNI), a known promoter of neurite outgrowth in cell culture and a potent inhibitor of serine proteases, also enhances neuronal cell survival. PNI, in nanomolar concentrations, rescues spinal cord motor neurons from both naturally-occurring programmed cell death in the chick embryo as well as following injury in the neonatal mouse. The potent neuromodulator, vasoactive intestinal polypeptide (VIP), influences neuronal survival through glial-mediated factors and also induces secretion of newly synthesized astrocyte PNI. We now report that subnanomolar amounts of PNI enhance neuronal survival in mixed spinal cord cell culture, especially when neuronal cells were made electrically silent by administration of tetrodotoxin. The mediation of this effect is by inhibition of the multifunctional serine protease, thrombin, because hirudin, a thrombin-specific inhibitor, has the same effect. In addition, spinal cord neurons are exquisitely sensitive to thrombin because picomolar and lower levels of the coagulation factor causes neuronal death. Thus, PNI is an astrocyte-derived, thrombin-inhibiting, activity-dependent neurotrophic agent, enhanced secretion of which by VIP may be one approach to treat neurological disorders.

Complete set of eleven region-specific microdissection libraries for human chromosome 2

The construction and characterization of 11 region-specific libraries for the entire human chromosome 2 have been completed, including four libraries for the short arm and six libraries for the long arm, plus a library for the centromere region. These libraries were constructed using the chromosome microdissection and microcloning technology. Eight libraries have been described previously. This paper presents the final three libraries: 2q21-q22 (designated 2Q5 library), 2q11-q14 (2Q6). and 2p11.1-q11.1 (2CEN). The sizes of the dissected regions ranged between 20 and 30 Mb, with the centromere region of about 4 Mb. All these libraries are large, potentially comprising hundreds of thousands of recombinant microclones. Between 77% and 97% of the microclones were shown to derive from respective dissected regions. From 26 to 66 unique sequence microlones were isolated and characterized in detail for each library. The microclones have short inserts, ranging between 50 and 600 bp, with a mean of about 200 bp. The short inserts can be conveniently sequenced as STSs to provide high density probes for the dissected region. A plasmid sub-library containing at least 20,000 microclones, and usually more, has been prepared from each library and deposited to ATCC for general distribution. The libraries have been used effectively in constructing high resolution physical maps and for contig assembly, as well as in positional cloning of disease genes assigned to the dissected region. Comparing to other chromosomes with detailed mapping information and densely populated probes, chromosome 2 remains largely under-exploited. The availability of a complete set of region-specific libraries and unique sequence microclones from the libraries should provide valuable resources for genome analysis, high resolution physical mapping, region-specific cDNA isolation, and positional cloning for chromosome 2.

Three region-specific microdissection libraries for the long arm of human chromosome 2, regions q33-q35, q31-q32, and q23-q24

Three region-specific libraries have been constructed from the long arm of human chromosome 2, including regions 2q33-35 (2Q2 library), 2q31-32 (2Q3) and 2q23-24 (2Q4). Chromosome microdissection and the MboI linker-adaptor microcloning techniques were used in constructing these libraries. The libraries comprised hundreds of thousands of microclones in each library. Approximately half of the microclones in the library contained unique or low-copy number sequence inserts. The insert sizes ranged between 50 and 800 bp, with a mean of 130-190 bp. Southern blot analysis of individual unique sequence microclones showed that 70-94% of the microclones were derived from the dissected region. 31 unique sequence microclones from the 2Q2 library, 31 from 2Q3, and 30 from 2Q4, were analyzed for insert sizes, the hybridizing genomic HindIII fragment sizes, and cross-hybridization to rodent species. These libraries and the short insert microclones derived from the libraries should be useful for high resolution physical mapping, sequence-ready reagents for large scale genomic sequencing, and positional cloning of disease-related genes assigned to these regions, e.g. the recessive familial amyotrophic lateral sclerosis assigned to 2q33-q35, and a type I diabetes susceptibility gene to 2q31-q33.

Amyotrophic lateral sclerosis is a multifactorial disease

Amyotrophic lateral sclerosis (ALS) is probably biphasic. An initial trigger(s) is followed by a terminal cascade coinciding with the onset of neurological deficits. The terminal cascade involves interactive multifactorial pathogenic mechanisms. Aging must play a crucial role leading to multiple defective or degraded gene products accumulating with progressing years. This in turn leads to failure of receptor integrity and resulting excitotoxicity, free radical accumulation, failure of neurotrophism, and possibly immunological disturbances. These events are predated by months or years by a trigger which is also likely to be multifactorial and cumulative. Evidence suggests that environmental factors may be important triggers. Failure of specific glutamate transporters and calcium binding proteins may account for selective vulnerability of the corticomotoneuronal system. It is postulated that in ALS the primary target cell is the corticomotoneuron or the local circuit interneurons which modulate its activity. Glia cells may play an important role in the demise of the corticomotoneuronal cell. The disordered corticomotoneuron induces excessive excitatory transmitter (glutamate?) release at the corticomotoneuronal-spinal-motoneuronal synapse resulting in the subsequent demise of this neuron.

Mechanisms in motor neurone disease: clues from genetic studies

Motor neurone disease is a rapidly progressive neurodegenerative disorder, characterized by muscular weakness and wasting with fasciculation and by spasticity. While most cases are sporadic, approximately 10% are inherited in an autosomal dominant mode. Recently, mutations in the gene encoding the free-radical scavenging enzyme superoxide dismutase-1 have been found to segregate with the disorder in 20% of familial cases. This is an exciting development, as free radical damage has long been implicated in the pathogenesis of motor neurone disease and it raises the possibility of novel therapeutic approaches in this otherwise fatal condition.

Sporadic ALS and chromosome 22: evidence for a possible neurofilament gene defect

ALS is associated with the P2 blood group phenotype. Molecular evidence now shows the gene encoding this antigen to be on the long arm of human chromosome 22 near the newly discovered gene for heavy neurofilament (NF-H). Since an ALS-type condition can be generated in transgenic mice expressing the human NF-H gene, and since the gene for the CNTF-related cytokine leukemia inhibitory factor (LIF) is located adjacent to this gene, it is hypothesized that a defect on the chromosome 22 band region q12 is involved in the pathogenesis of sporadic ALS.

Amyotrophic lateral sclerosis associated with homozygosity for an Asp90Ala mutation in CuZn-superoxide dismutase

Recent reports have shown heterozygosity for some twenty different mutations in the CuZn-superoxide dismutase (CuZn-SOD) gene in familial amyotrophic lateral sclerosis (FALS), and analysed samples from patients have shown decreased enzymic activity. Here we report homozygosity for an exon 4 mutation, Asp90Ala in fourteen patients among four unrelated ALS families and four apparently sporadic ALS patients from Sweden and Finland. The erythrocyte CuZn-SOD activity is essentially normal. Our findings suggest that this CuZn-SOD mutation causes ALS by a gain of function rather than by loss, and that the Asp90Ala mutation is less detrimental than previously reported mutations.

Analysis of aldehyde oxidase and xanthine dehydrogenase/oxidase as possible candidate genes for autosomal recessive familial amyotrophic lateral sclerosis

Recently, point mutations in superoxide dismutase 1 (SOD1) have been shown to lead to a subset of autosomal dominantly inherited familial amyotrophic lateral sclerosis (ALS). These findings have led to the hypothesis that defects in oxygen radical metabolism may be involved in the pathogenesis of ALS. Therefore, we decided to analyze other enzymes involved in oxygen radical metabolism for possible involvement in other forms of ALS. We report here analysis of two genes encoding the molybdenum hydroxylases aldehyde oxidase (AO) and xanthine dehydrogenase/oxidase (XDH) for involvement in ALS. Of particular interest, one gene identified as encoding aldehyde oxidase is shown to map to 2q33, a region recently shown to contain a gene responsible for a familial form of ALS with autosomal recessive inheritance (FALS-AR). The AO gene appears to be located within 280,000 bp of simple sequence repeat marker D2S116, which shows no recombination with the FALS-AR locus. The AO gene is highly expressed in glial cells of human spinal cord. In addition, we mapped a gene for XDH to 2p22, a region previously shown to contain a highly homologous but different form of XDH. Neither of these XDH genes appears to be highly expressed in human spinal cord. This evidence suggests that AO may be a candidate gene for FALS-AR.