Identification of APTX disease-causing mutation in two unrelated Jordanian families with cerebellar ataxia and sensitivity to DNA damaging agents.

BACKGROUND: Ataxia with oculomotor apraxia type 1 (AOA1) is a rare autosomal recessive cerebellar ataxia, caused by mutations in the APTX gene. The disease is characterized by early-onset cerebellar ataxia, oculomotor apraxia and severe axonal polyneuropathy. The aim of this study was to detect the disease-causing variants in two unrelated consanguineous Jordanian families with cerebellar ataxia using whole exome sequencing (WES), and to correlate the identified mutation(s) with the clinical and cellular phenotypes. METHODS: WES was performed in three affected individuals and segregation analysis of p.W279* APTX candidate variant was performed. Expression levels of APTX were measured in patients' skin fibroblasts and peripheral blood mononuclear cells, followed by western blot analysis in skin fibroblasts. Genotoxicity assay was performed to detect the sensitivity of APTX mutated cells to H2O2, MMC, MMS and etoposide. RESULTS: A recurrent homozygous nonsense variant in APTX gene (c.837G>A, p.W279*) was revealed in all affected individuals. qRT-PCR showed normal APTX levels in peripheral blood and lower levels in fibroblast cells. However, western blot showed the absence of APTX protein in patients' skin fibroblasts. Significant hypersensitivity to H2O2, MMC and etoposide and lack of sensitivity to MMS were noted. CONCLUSIONS: This is the first study to report the identification of a nonsense variant in the APTX gene (c.837G>A; p.W279*) in AOA1 patients within the Jordanian population. This study confirmed the need of WES to assist in the diagnosis of cerebellar ataxia and it emphasizes the importance of studying the pathophysiology of the APTX gene.

Generation and characterization of induced pluripotent stem cell (iPSC) line (JUCTCi002-A) from a patient with ataxia with oculomotor apraxia type 1 (AOA1) harboring a homozygous mutation in the APTX gene.

Ataxia with Oculomotor Apraxia Type 1 (AOA1) is an autosomal-recessive cerebellar ataxia characterized by early-onset cerebellar atrophy and axonal sensorimotor polyneuropathy. AOA1 is related to mutations in the aprataxin (APTX) gene encoding for the aprataxin protein. The aprataxin protein has been reported to be involved in DNA single-strand break repair (SSBR) machinery and it localizes to the mitochondria to preserve the mitochondrial function. Here, we demonstrate the generation of induced pluripotent stem cell (iPSC) line (JUCTCi002-A) from AOA1 patient's skin dermal fibroblasts. The selected line showed normal karyotype, expression of pluripotency markers and the ability to differentiatie in vitro into the three germ layers.