Complete deletion of the aprataxin gene: Ataxia with oculomotor apraxia type 1 with severe phenotype and cognitive deficit

University of Toronto, 555 University Avenue, Ontario, M5G 1X8, Canada.
Case Reports 02/2009; 2009. DOI: 10.1136/bcr.08.2008.0688
Source: PubMed


Ataxia with oculomotor apraxia type 1 (AOA1) is a recently described autosomal-recessive neurodegenerative condition of childhood onset. It is caused by mutations in the APTX gene, which encodes the protein aprataxin. Clinical features include gait and limb ataxia, dysarthria, oculomotor apraxia, mild peripheral neuropathy and progression of neurological deficits.1 Some patients manifest parkinsonian symptoms or mental retardation, although the latter has been reported predominantly in Japanese patients.2 We report a patient with homozygous deletion of APTX, who presented with behavioural changes (social withdrawal), and subsequent rapid progression of neurological symptoms associated with severe cognitive decline. We suggest that complete deletion of APTX is associated with a more severe phenotype than that associated with point mutations.

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    ABSTRACT: DNA single-strand breaks (SSBs) are non-overlapping discontinuities in strands ofa DNA duplex. Significant attention has been given on the DNA SSB repair (SSBR) system in neurons, because the impairment of the SSBR causes human neurodegenerative disorders, including early-onset ataxia with ocular motor apraxia and hypoalbuminemia (EAOH), also known as ataxia-oculomotor apraxia Type 1 (AOA1). EAOH/AOA1 is characterized by early-onset slowly progressive ataxia, ocular motor apraxia, peripheral neuropathy and hypoalbuminemia. Neuropathological examination reveals severe loss of Purkinje cells and moderate neuronal loss in the anterior horn and dorsal root ganglia. EAOH/AOA1 is caused by the mutation in the APTX gene encoding the aprataxin (APTX) protein. APTX interacts with X-ray repair cross-complementing group 1 protein, which is a scaffold protein in SSBR. In addition, APTX-defective cells show increased sensitivity to genotoxic agents, which result in SSBs. These results indicate an important role ofAPTX in SSBR. SSBs are usually accompanied by modified or damaged 5'- and 3'-ends at the break site. Because these modified or damaged ends are not suitable for DNA ligation, they need to be restored to conventional ends prior to subsequent repair processes. APTX restores the 5'-adenylate monophosphate, 3'-phosphates and 3'-phosphoglycolate ends. The loss of function of APTX results in the accumulation of SSBs, consequently leading to neuronal cell dysfunction and death.
    Advances in Experimental Medicine and Biology 01/2010; 685:21-33. DOI:10.1007/978-1-4419-6448-9_3 · 1.96 Impact Factor
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    ABSTRACT: Background Autosomal recessive ataxias represent a group of clinically overlapping disorders. These include ataxia with oculomotor apraxia type1 (AOA1), ataxia with oculomotor apraxia type 2 (AOA2) and ataxia-telangiectasia-like disease (ATLD). Patients are mainly characterized by cerebellar ataxia and oculomotor apraxia. Although these forms are not quite distinctive phenotypically, different genes have been linked to these disorders. Mutations in the APTX gene were reported in AOA1 patients, mutations in SETX gene were reported in patients with AOA2 and mutations in MRE11 were identified in ATLD patients. In the present study we describe in detail the clinical features and results of genetic analysis of 9 patients from 4 Saudi families with ataxia and oculomotor apraxia. Methods This study was conducted in the period between 2005-2010 to clinically and molecularly characterize patients with AOA phenotype. Comprehensive sequencing of all coding exons of previously reported genes related to this disorder (APTX, SETX and MRE11). Results A novel nonsense truncating mutation c.6859 C > T, R2287X in SETX gene was identified in patients from one family with AOA2. The previously reported missense mutation W210C in MRE11 gene was identified in two families with autosomal recessive ataxia and oculomotor apraxia. Conclusion Mutations in APTX , SETX and MRE11 are common in patients with autosomal recessive ataxia and oculomotor apraxia. The results of the comprehensive screening of these genes in 4 Saudi families identified mutations in SETX and MRE11 genes but failed to identify mutations in APTX gene.
    BMC Medical Genetics 02/2011; 12. DOI:10.1186/1471-2350-12-27 · 2.08 Impact Factor