Novel mutations in ATP13A2 associated with mixed neurological presentations and iron toxicity due to nonsense-mediated decay

Background: Kufor-Rakeb Syndrome (KRS) is an autosomal recessive disease characterized by Parkinsonism, pyramidal signs, dementia, and supranuclear gaze palsy. KRS is caused by mutations in ATP13A2 producing a transmembrane protein responsible for the regulation of intracellular inorganic cations. Objective: Two siblings born to a Turkish family of consanguineous marriage had mixed neurological presentations with the presence of hypointense images on T2-weighted MRI and were pre-diagnosed as having autosomal recessive spastic paraparesis or ataxia. We aimed to identify the disease-causing mutation by whole-exome sequencing and elucidate the underlying molecular mechanism of the causative mutation. Methods: Prussian blue staining was conducted for the detection of cellular iron accumulation. Disease-causing mutation in ATP13A2 was detected by whole-exome sequencing. Expression levels of ATP13A2 mRNA and protein were assessed by qRT-PCR and Western Blot. Results: Iron deposits in the patients’ fibroblasts were detected by Prussian blue staining. Novel homozygous mutation c.1422_1423del:p.P474fs was detected in the ATP13A2. As this mutation caused a premature termination codon (PTC), the expression of mutant ATP13A2 mRNA through qRT-PCR analysis was found to be degraded by nonsense-mediated decay and this prevented the expression of ATP13A2 protein in the patients’ fibroblasts. Conclusions: Novel frameshift mutation causing a PTC in ATP13A2 lead to degradation of ATP13A2 mRNA by NMD. Iron accumulation due to the absence of ATP13A2 protein in the patient's fibroblasts and hypointense areas on T2-weighted images may expand the spectrum of KRS to consider it as neurodegeneration with brain iron accumulation disorders.