Abnormal dentatorubral-pallidoluysian atrophy (DRPLA) protein complex is pathologically ubiquitinated in DRPLA brains.

Dentatorubral-pallidoluysian atrophy (DRPLA) is caused by expansion of a glutamine repeat in DRPLA protein. DRPLA protein undergoes greater complex formation in DRPLA brain tissue, and expanded glutamine repeat enhances complex formation of DRPLA protein. Immunoblots with and without reduction show that the DRPLA protein complex is ubiquitinated only in DRPLA brain tissue. Moreover, immunoblots of regional DRPLA brain tissues reveal that pathological ubiquitination of DRPLA protein complex is found selectively in affected lesions. Double-labeling immunohistochemical studies with antibodies against DRPLA protein and ubiquitin demonstrate that the DRPLA protein is co-localized with ubiquitin in DRPLA neurons and show characteristic neuronal cytoplasmic inclusions with ubiquitinated DRPLA protein complex in the center. Our findings suggest that DRPLA protein undergoes abnormal complex formation with expanded glutamine repeat, and then the complex is pathologically ubiquitinated in DRPLA brain tissue. Pathological ubiquitination of abnormal DRPLA protein complex plays a role in DRPLA pathology.     

Distribution of CAG repeat size in the dentatorubral and pallidoluysian atrophy (DRPLA) gene in a normal population in Taiwan

Dentatorubral and pallidoluysian atrophy (DRPLA) is an autosomal dominant neurodegenerative disorder with expansion of trinucleotide CAG repeats in the coding region of the gene. Expansion of the repeat tract beyond the normal range produces gene products with extended polyglutamine tracts. In this study, we analyzed the distribution of the CAG repeats in the DRPLA alleles in a normal Taiwanese population. We observed 15 different alleles and found that the range of the CAG repeat number was from 7-21. The most frequent allele contained 15 CAG repeats that represented 20% of the total analyzed alleles, followed by the 17 repeats (15.8%). The heterozygosity rate of this locus was 88%. Twelve parents-to-children transmissions of the DRPLA alleles in a Machado-Joseph disease family appeared to be normal without any alteration of the CAG repeat numbers. Phenotypes of DRPLA overlapped those of autosomal dominant cerebellar ataxia (ADCA). In order to identify DRPLA patients in Taiwan, we screened six autosomal dominant cerebellar ataxia patients without expansion in known spinocerebellar ataxia genes. All six patients had the repeat numbers within the normal range; thus, the possibility of DRPLA could be excluded.     

Differential somatic CAG repeat instability in variable brain cell lineage in dentatorubral pallidoluysian atrophy (DRPLA): a laser-captured microdissection (LCM)-based analysis

Employing a laser-captured microdissection (LCM), we have investigated the somatic instability of CAG repeats in the variable brain cell lineage in three patients with dentatorubral pallidoluysian atrophy (DRPLA). LCM enables the isolation of single lineage brain cells for subsequent molecular analysis. We have found that CAG repeat size and the range of CAG repeats in the cerebellar granular cells is smaller than those in cerebellar glial cells. Similarly, those in the cerebral neuronal cells are significantly shorter than those in cerebral glial cells. These data directly indicate that the CAG repeat is relatively more stable in neuronal cells than in glial cells. Furthermore, cerebellar granular cells show significantly smaller main CAG repeat size and CAG repeat range than either Purkinje cells or cerebral neuronal cells, suggesting that somatic instability in the CAG repeat is markedly variable even among the different types of neuronal populations. The cell-specific CAG repeat instability may thus be more complex than has previously been considered. LCM is a powerful tool for elucidating the mechanism of the triplet repeat instability of each cell type.     

Linkage analysis in dominant optic atrophy

A kindred of German descent was studied for dominant optic atrophy, type Kjer (McKusick catalog no. 16540). One hundred twenty-three family members were examined clinically, and 36 affected, 81 normal, and six uncertain members were ascertained. Twenty-seven markers were analyzed for 121 members. The maximum lod score obtained was 2.0 at theta = .18 for linkage between the Kidd locus and dominant optic atrophy. Twenty-eight offspring were informative with 2-generation data. There was insufficient information for the acid phosphatase locus to aid gene localization. These data suggest that the locus for dominant optic atrophy is on chromosome 2.     

Dentatorubral-pallidoluysian atrophy (DRPLA): Close correlation of CAG repeat expansions with the wide spectrum of clinical presentations and prominent anticipation

Dentatorubral-pallidoluysian atrophy (DRPLA) is a rare autosomal dominant neurodegenerative disease characterized by various combinations of ataxia, choreoathetosis, myoclonus, epilepsy and dementia as well as various ages of onset. We have identified a specific unstable trinucleotide repeat expansion in a gene on the short arm of chromosome 12 as the pathogenic mutation for DRPLA. We investigated how the degree of the expansion of the CAG repeat affects the clinical manifestations of DRPLA. The sizes of the expanded alleles were well correlated with the ages of onset (r = −0.6955, P < 0.001). Patients with progressive myoclonus epilepsy (PME) phenotype had larger expansions (62–79 repeats) and earlier ages of onset (onset before age 20). Furthermore, most of the patients with PME phenotype inherited their expanded alleles from their affected fathers. On the other hand, patients with non-PME phenotype showed later ages of onset (onset after age 20) and smaller expansions (54–67 repeats). When ages of onset of each clinical symptom are compared with sizes of the CAG repeat, there is again a remarkably high correlation of the sizes of CAG repeat with each of the clinical symptoms. Thus the wide variation in clinical manifestations of DRPLA can now be clearly explained based on the degree of CAG repeat expansion, which strongly indicates that the expanded alleles are intimately involved in the neuronal degeneration in dentatofugal and pallidofugal systems.     

Precise chromosomal locations of the genes for dentatorubral-pallidoluysian atrophy (DRPLA), von Willebrand factor (F8vWF) and parathyroid hormone-like hormone (PTHLH) in human chromosome 12p by deletion mapping

The precise chromosomal localization of the gene for dentatorubral-pallidoluysian atrophy (DRPLA) was detected by deletion mapping. Segregation patterns of genotypes of polymerase chain reaction products of DRPLA, von Willebrand factor (F8vWF), antigen CD4(p55) (CD4) and parathyroid hormone-like hormone (PTHLH) loci were studied in patients with del(12)(p13.3p13.3), del(12)(p12.3-p11.2), del(12)(p12.1-p11.2), del(12) (p11.2p11.2) and their parents. The gene for DRPLA was assigned to p13.1-p12.3 of chromosome 12. In addition, genes for F8vWF and PTHLH were mapped to p13.2 and p11.2 of chromosome 12, respectively.     

A nonsense mutation in the optic atrophy 3 gene (OPA3) causes dilated cardiomyopathy in Red Holstein cattle

Cardiomyopathies are severe degenerative disorders of the myocardium that lead to heart failure. During the last three decades bovine dilated cardiomyopathy (BDCMP) was observed worldwide in cattle of Holstein-Friesian origin. In the Swiss cattle population BDCMP affects Fleckvieh and Red Holstein breeds. The heart of affected animals is enlarged due to dilation of both ventricles. Clinical signs are caused by systolic dysfunction and affected individuals die as a result of severe heart insufficiency. BDCMP follows an autosomal recessive pattern of inheritance and the disease-causing locus was mapped to bovine chromosome 18 (BTA18). In the present study we describe the successful identification of the causative mutation in the OPA3 gene located on BTA18 that was previously reported to cause 3-methylglutaconic aciduria type III in Iraqi-Jewish patients. We demonstrated conclusive genetic and functional evidence that the nonsense mutation c.343C>T in the bovine OPA3 gene causes the late-onset dilated cardiomyopathy in Red Holstein cattle.     

Autophagy controls the pathogenicity of OPA1 mutations in dominant optic atrophy

Optic Atrophy 1 (OPA1) gene mutations cause diseases ranging from isolated dominant optic atrophy (DOA) to various multisystemic disorders. OPA1, a large GTPase belonging to the dynamin family, is involved in mitochondrial network dynamics. The majority of OPA1 mutations encodes truncated forms of the protein and causes DOA through haploinsufficiency, whereas missense OPA1 mutations are predicted to cause disease through deleterious dominant‐negative mechanisms. We used 3D imaging and biochemical analysis to explore autophagy and mitophagy in fibroblasts from seven patients harbouring OPA1 mutations. We report new genotype–phenotype correlations between various types of OPA1 mutation and mitophagy. Fibroblasts bearing dominant‐negative OPA1 mutations showed increased autophagy and mitophagy in response to uncoupled oxidative phosphorylation. In contrast, OPA1 haploinsufficiency was correlated with a substantial reduction in mitochondrial turnover and autophagy, unless subjected to experimental mitochondrial injury. Our results indicate distinct alterations of mitochondrial physiology and turnover in cells with OPA1 mutations, suggesting that the level and profile of OPA1 may regulate the rate of mitophagy.