TARDBP mutations in individuals with sporadic and familial amyotrophic lateral sclerosis

Recently, TDP-43 was identified as a key component of ubiquitinated aggregates in amyotrophic lateral sclerosis (ALS), an adult-onset neurological disorder that leads to the degeneration of motor neurons. Here we report eight missense mutations in nine individuals--six from individuals with sporadic ALS (SALS) and three from those with familial ALS (FALS)--and a concurring increase of a smaller TDP-43 product. These findings further corroborate that TDP-43 is involved in ALS pathogenesis.     

ANG mutations segregate with familial and 'sporadic' amyotrophic lateral sclerosis

We recently identified angiogenin (ANG) as a candidate susceptibility gene for amyotrophic lateral sclerosis (ALS), a neurodegenerative disorder characterized by adult-onset loss of motor neurons. We now report the finding of seven missense mutations in 15 individuals, of whom four had familial ALS and 11 apparently 'sporadic' ALS. Our findings provide further evidence that variations in hypoxia-inducible genes have an important role in motor neuron degeneration.     

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).     

Mutations in mRNA export mediator GLE1 result in a fetal motoneuron disease

The most severe forms of motoneuron disease manifest in utero are characterized by marked atrophy of spinal cord motoneurons and fetal immobility. Here, we report that the defective gene underlying lethal motoneuron syndrome LCCS1 is the mRNA export mediator GLE1. Our finding of mutated GLE1 exposes a common pathway connecting the genes implicated in LCCS1, LCCS2 and LCCS3 and elucidates mRNA processing as a critical molecular mechanism in motoneuron development and maturation.     

CFH haplotypes without the Y402H coding variant show strong association with susceptibility to age-related macular degeneration

In developed countries, age-related macular degeneration is a common cause of blindness in the elderly. A common polymorphism, encoding the sequence variation Y402H in complement factor H (CFH), has been strongly associated with disease susceptibility. Here, we examined 84 polymorphisms in and around CFH in 726 affected individuals (including 544 unrelated individuals) and 268 unrelated controls. In this sample, 20 of these polymorphisms showed stronger association with disease susceptibility than the Y402H variant. Further, no single polymorphism could account for the contribution of the CFH locus to disease susceptibility. Instead, multiple polymorphisms defined a set of four common haplotypes (of which two were associated with disease susceptibility and two seemed to be protective) and multiple rare haplotypes (associated with increased susceptibility in aggregate). Our results suggest that there are multiple disease susceptibility alleles in the region and that noncoding CFH variants play a role in disease susceptibility.     

Spontaneous activity of opsin apoprotein is a cause of Leber congenital amaurosis

Mutations in Rpe65 disrupt synthesis of the opsin chromophore ligand 11-cis-retinal and cause Leber congenital amaurosis (LCA), a severe, early-onset retinal dystrophy. To test whether light-independent signaling by unliganded opsin causes the degeneration, we used Rpe65-null mice, a model of LCA. Dark-adapted Rpe65-/- mice behaved as if light adapted, exhibiting reduced circulating current, accelerated response turn-off, and diminished intracellular calcium. A genetic block of transducin signaling completely rescued degeneration irrespective of an elevated level of retinyl ester. These studies clearly show that activation of sensory transduction by unliganded opsin, and not the accumulation of retinyl esters, causes light-independent retinal degeneration in LCA. A similar mechanism may also be responsible for degeneration induced by vitamin A deprivation.     

Genetic inroads in familial ALS

Amyotrophic lateral sclerosis (ALS) is a common neurodegenerative disease causing cell death of motor neurons and progressive muscle weakness. The disease is familial in ten percent of cases, of which one-fifth are due to mutations in the gene encoding Cu/Zn superoxide dismutase (SOD1). Two papers in this issue of Nature Genetics describe homozygous mutations in a new gene on chromosome 2q33 in 4 families of Arabian origin with a rare form of juvenile onset ALS (ALS2). The predicted protein structure has domains homologous to GTPase regulatory proteins, and both the types of mutation and the pattern of inheritance suggest that motor neuron degeneration is the result of a loss of function. Further work will determine the relevance of this breakthrough to other, more common forms of ALS.     

Uncontrolled C3 activation causes membranoproliferative glomerulonephritis in mice deficient in complement factor H

The alternative pathway of complement is activated continuously in vivo through the C3 'tick-over' pathway. This pathway is triggered by the hydrolysis of C3, resulting in the formation of C3 convertase. This, in turn, generates C3b, which mediates many of the biological functions of complement. Factor H, the main regulator of this activation, prevents formation and promotes dissociation of the C3 convertase enzyme, and, together with factor I, mediates the proteolytic inactivation of C3b. Factor H deficiency, described in 29 individuals from 12 families and in pigs, allows unhindered activation of fluid-phase C3 and severe depletion of plasma C3 (ref. 11). Membranoproliferative glomerulonephritis (MPGN) occurs in factor H-deficient humans and pigs. Although MPGN has been reported in other conditions in which uncontrolled activation of C3 occurs, the role of C3 dysregulation in the pathogenesis of MPGN is not understood. Here we show that mice deficient in factor H (Cfh(-/-) mice) develop MPGN spontaneously and are hypersensitive to developing renal injury caused by immune complexes. Introducing a second mutation in the gene encoding complement factor B, which prevents C3 turnover in vivo, obviates the phenotype of Cfh(-/-) mice. Thus, uncontrolled C3 activation in vivo is essential for the development of MPGN associated with deficiency of factor H.     

Variation in factor B (BF) and complement component 2 (C2) genes is associated with age-related macular degeneration

Age-related macular degeneration (AMD) is the most common form of irreversible blindness in developed countries. Variants in the factor H gene (CFH, also known as HF1), which encodes a major inhibitor of the alternative complement pathway, are associated with the risk for developing AMD. Here we test the hypothesis that variation in genes encoding other regulatory proteins of the same pathway is associated with AMD. We screened factor B (BF) and complement component 2 (C2) genes, located in the major histocompatibility complex class III region, for genetic variation in two independent cohorts comprising approximately 900 individuals with AMD and approximately 400 matched controls. Haplotype analyses identify a statistically significant common risk haplotype (H1) and two protective haplotypes. The L9H variant of BF and the E318D variant of C2 (H10), as well as a variant in intron 10 of C2 and the R32Q variant of BF (H7), confer a significantly reduced risk of AMD (odds ratio = 0.45 and 0.36, respectively). Combined analysis of the C2 and BF haplotypes and CFH variants shows that variation in the two loci can predict the clinical outcome in 74% of the affected individuals and 56% of the controls. These data expand and refine our understanding of the genetic risk for AMD.     

Rom-1 is required for rod photoreceptor viability and the regulation of disk morphogenesis

The homologous membrane proteins Rom-1 and peripherin-2 are localized to the disk rims of photoreceptor outer segments (OSs), where they associate as tetramers and larger oligomers. Disk rims are thought to be critical for disk morphogenesis, OS renewal and the maintenance of OS structure, but the molecules which regulate these processes are unknown. Although peripherin-2 is known to be required for OS formation (because Prph2-/- mice do not form OSs; ref. 6), and mutations in RDS (the human homologue of Prph2) cause retinal degeneration, the relationship of Rom-1 to these processes is uncertain. Here we show that Rom1-/- mice form OSs in which peripherin-2 homotetramers are localized to the disk rims, indicating that peripherin-2 alone is sufficient for both disk and OS morphogenesis. The disks produced in Rom1-/- mice were large, rod OSs were highly disorganized (a phenotype which largely normalized with age) and rod photoreceptors died slowly by apoptosis. Furthermore, the maximal photoresponse of Rom1-/- rod photoreceptors was lower than that of controls. We conclude that Rom-1 is required for the regulation of disk morphogenesis and the viability of mammalian rod photoreceptors, and that mutations in human ROM1 may cause recessive photoreceptor degeneration.     

A rare variant in CFH directly links age-related macular degeneration with rare glomerular nephropathies

A careful analysis of risk haplotypes in relation to age-related macular degeneration (AMD) susceptibility has led to the identification of a rare, high-penetrance variant in the complement factor H (CFH) gene that is also causally associated with atypical hemolytic uremic syndrome (aHUS) and related glomerulopathies. This finding provides a convincing causal mechanism linking the two diseases and develops a paradigm for the genetic architecture of a common and complex disease.     

Structural diversity and African origin of the 17q21.31 inversion polymorphism

The 17q21.31 inversion polymorphism exists either as direct (H1) or inverted (H2) haplotypes with differential predispositions to disease and selection. We investigated its genetic diversity in 2,700 individuals, with an emphasis on African populations. We characterize eight structural haplotypes due to complex rearrangements that vary in size from 1.08-1.49 Mb and provide evidence for a 30-kb H1-H2 double recombination event. We show that recurrent partial duplications of the KANSL1 gene have occurred on both the H1 and H2 haplotypes and have risen to high frequency in European populations. We identify a likely ancestral H2 haplotype (H2') lacking these duplications that is enriched among African hunter-gatherer groups yet essentially absent from West African populations. Whereas H1 and H2 segmental duplications arose independently and before human migration out of Africa, they have reached high frequencies recently among Europeans, either because of extraordinary genetic drift or selective sweeps.     

Mitochondrial dysfunction and apoptosis in myopathic mice with collagen VI deficiency

Collagen VI is an extracellular matrix protein that forms a microfilamentous network in skeletal muscles and other organs. Inherited mutations in genes encoding collagen VI in humans cause two muscle diseases, Bethlem myopathy and Ullrich congenital muscular dystrophy. We previously generated collagen VI-deficient (Col6a1-/-) mice and showed that they have a muscle phenotype that strongly resembles Bethlem myopathy. The pathophysiological defects and mechanisms leading to the myopathic disorder were not known. Here we show that Col6a1-/- muscles have a loss of contractile strength associated with ultrastructural alterations of sarcoplasmic reticulum (SR) and mitochondria and spontaneous apoptosis. We found a latent mitochondrial dysfunction in myofibers of Col6a1-/- mice on incubation with the selective F1F(O)-ATPase inhibitor oligomycin, which caused mitochondrial depolarization, Ca2+ deregulation and increased apoptosis. These defects were reversible, as they could be normalized by plating Col6a1-/- myofibers on collagen VI or by addition of cyclosporin A (CsA), the inhibitor of mitochondrial permeability transition pore (PTP). Treatment of Col6a1-/- mice with CsA rescued the muscle ultrastructural defects and markedly decreased the number of apoptotic nuclei in vivo. These findings indicate that collagen VI myopathies have an unexpected mitochondrial pathogenesis that could be exploited for therapeutic intervention.     

Mice deficient in protein tyrosine phosphatase receptor type Z are resistant to gastric ulcer induction by VacA of Helicobacter pylori

The vacuolating cytotoxin VacA produced by Helicobacter pylori causes massive cellular vacuolation in vitro and gastric tissue damage in vivo, leading to gastric ulcers, when administered intragastrically. Here we report that mice deficient in protein tyrosine phosphatase receptor type Z (Ptprz, also called PTP-zeta or RPTP-beta, encoded by Ptprz) do not show mucosal damage by VacA, although VacA is incorporated into the gastric epithelial cells to the same extent as in wild-type mice. Primary cultures of gastric epithelial cells from Ptprz+/+ and Ptprz-/- mice also showed similar incorporation of VacA, cellular vacuolation and reduction in cellular proliferation, but only Ptprz+/+ cells showed marked detachment from a reconstituted basement membrane 24 h after treatment with VacA. VacA bound to Ptprz, and the levels of tyrosine phosphorylation of the G protein-coupled receptor kinase-interactor 1 (Git1), a Ptprz substrate, were higher after treatment with VacA, indicating that VacA behaves as a ligand for Ptprz. Furthermore, pleiotrophin (PTN), an endogenous ligand of Ptprz, also induced gastritis specifically in Ptprz+/+ mice when administered orally. Taken together, these data indicate that erroneous Ptprz signaling induces gastric ulcers.     

Dysregulation of TGF-beta activation contributes to pathogenesis in Marfan syndrome

Marfan syndrome is an autosomal dominant disorder of connective tissue caused by mutations in fibrillin-1 (encoded by FBN1 in humans and Fbn1 in mice), a matrix component of extracellular microfibrils. A distinct subgroup of individuals with Marfan syndrome have distal airspace enlargement, historically described as emphysema, which frequently results in spontaneous lung rupture (pneumothorax; refs. 1-3). To investigate the pathogenesis of genetically imposed emphysema, we analyzed the lung phenotype of mice deficient in fibrillin-1, an accepted model of Marfan syndrome. Lung abnormalities are evident in the immediate postnatal period and manifest as a developmental impairment of distal alveolar septation. Aged mice deficient in fibrillin-1 develop destructive emphysema consistent with the view that early developmental perturbations can predispose to late-onset, seemingly acquired phenotypes. We show that mice deficient in fibrillin-1 have marked dysregulation of transforming growth factor-beta (TGF-beta) activation and signaling, resulting in apoptosis in the developing lung. Perinatal antagonism of TGF-beta attenuates apoptosis and rescues alveolar septation in vivo. These data indicate that matrix sequestration of cytokines is crucial to their regulated activation and signaling and that perturbation of this function can contribute to the pathogenesis of disease.     

Identification of the gene causing mucolipidosis type IV

Mucolipidosis type IV (MLIV) is an autosomal recessive, neurodegenerative, lysosomal storage disorder characterized by psychomotor retardation and ophthalmological abnormalities including corneal opacities, retinal degeneration and strabismus. Most patients reach a maximal developmental level of 12?15 months. The disease was classified as a mucolipidosis following observations by electron microscopy indicating the lysosomal storage of lipids together with water-soluble, granulated substances. Over 80% of the MLIV patients diagnosed are Ashkenazi Jews, including severely affected and mildly affected patients. The gene causing MLIV was previously mapped to human chromosome 19p13.2-13.3 in a region of approximately 1 cM (ref. 7). Haplotype analysis in the MLIV gene region of over 70 MLIV Ashkenazi chromosomes indicated the existence of two founder chromosomes among 95% of the Ashkenazi MLIV families: a major haplotype in 72% and a minor haplotype in 23% of the MLIV chromosomes (ref. 7, and G.B., unpublished data). The remaining 5% are distinct haplotypes found only in single patients. The basic metabolic defect causing the lysosomal storage in MLIV has not yet been identified. Thus, positional cloning was an alternative to identify the MLIV gene. We report here the identification of a new gene in this human chromosomal region in which MLIV-specific mutations were identified.