Inherited ataxias are heterogeneous disorders affecting both children and adults, with over 40 different causative genes, making molecular genetic diagnosis challenging. Although recent advances in next-generation sequencing have significantly improved mutation detection, few treatments exist for patients with inherited ataxia. In two patients with adult-onset cerebellar ataxia and coenzyme Q10 (CoQ10) deficiency in muscle, whole exome sequencing revealed mutations in ANO10, which encodes anoctamin 10, a member of a family of putative calcium-activated chloride channels, and the causative gene for autosomal recessive spinocerebellar ataxia-10 (SCAR10). Both patients presented with slowly progressive ataxia and dysarthria leading to severe disability in the sixth decade. Epilepsy and learning difficulties were also present in one patient, while retinal degeneration and cataract were present in the other. The detection of mutations in ANO10 in our patients indicate that ANO10 defects cause secondary low CoQ10 and SCAR10 patients may benefit from CoQ10 supplementation.Electronic supplementary materialThe online version of this article (doi:10.1007/s00415-014-7476-7) contains supplementary material, which is available to authorized users.

Zebrafish (Danio rerio) express two isoforms of the type IIb Na-dependent P(i) cotransporter (NaPi). Type NaPi-IIb1 has previously been cloned and characterized. Here, we report the cloning of the NaPi-IIb2 transcript from zebrafish kidney, its localization, and its functional characterization. RT-PCR with renal RNA and degenerate NaPi-IIb-specific primers resulted in a specific fragment. 3'-Rapid amplification of cDNA ends yielded a product that contained typical NaPi-IIb characteristics such as a cysteine-rich COOH terminus and a PDZ (PSD95- Dlg-zona occludens-1) binding motif. Several approaches were unsuccessful at cloning the 5' end of the transcript; products lacked an in-frame start codon. The missing information was obtained from an EST (GenBank accession number ). The combined clone displayed a high degree of homology with published type IIb cotransporter sequences. Specific antibodies were raised against a COOH-terminal epitope of both NaPi-IIb1 and NaPi-IIb2 isoforms. Immunohistochemical mapping revealed apical expression of both isoforms in zebrafish renal and intestinal epithelia, as well as in bile ducts. The novel clone was expressed in oocytes, and function was assayed by the two-electrode voltage-clamp technique. The function of the new NaPi-IIb2 clone was found to be significantly different from NaPi-IIb1 despite strong structural similarities. NaPi-IIb2 was found to be strongly voltage sensitive, with higher affinities for both sodium and phosphate than NaPi-IIb1. Also, NaPi-IIb2 was significantly less sensitive to external pH than NaPi-IIb1. The strong structural similarity but divergent function makes these zebrafish transporters ideal models for the molecular mapping of functionally important regions in the type II NaPi-cotransporter family.

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