BackgroundPhosphoribosyl pyrophosphate synthetase (PRS) I deficiency is a rare medical condition caused by missense mutations in PRPS1 that lead to three different phenotypes: Arts Syndrome (MIM 301835), X-linked Charcot-Marie-Tooth (CMTX5, MIM 311070) or X-linked non-syndromic sensorineural deafness (DFN2, MIM 304500). All three are X-linked recessively inherited and males affected display variable degree of central and peripheral neuropathy. We applied whole exome sequencing to a three-generation family with optic atrophy followed by retinitis pigmentosa (RP) in all three cases, and ataxia, progressive peripheral neuropathy and hearing loss with variable presentation.MethodsWhole exome sequencing was performed in two affecteds and one unaffected member of the family. Sanger sequencing was used to validate and segregate the 12 candidate mutations in the family and to confirm the absence of the novel variant in PRPS1 in 191 controls. The pathogenic role of the novel mutation in PRPS1 was assessed in silico and confirmed by enzymatic determination of PRS activity, mRNA expression and sequencing, and X-chromosome inactivation.ResultsA novel missense mutation was identified in PRPS1 in the affected females. Age of onset, presentation and severity of the phenotype are highly variable in the family: both the proband and her mother have neurological and ophthalmological symptoms, whereas the phenotype of the affected sister is milder and currently confined to the eye. Moreover, only the proband displayed a complete lack of expression of the wild type allele in leukocytes that seems to correlate with the degree of PRS deficiency and the severity of the phenotype. Interestingly, optic atrophy and RP are the only common manifestations to all three females and the only phenotype correlating with the degree of enzyme deficiency.ConclusionsThese results are in line with recent evidence of the existence of intermediate phenotypes in PRS-I deficiency syndromes and demonstrate that females can exhibit a disease phenotype as severe and complex as their male counterparts.Electronic supplementary materialThe online version of this article (doi:10.1186/s13023-014-0190-9) contains supplementary material, which is available to authorized users.

Dystonia is a neurological movement disorder that is clinically and genetically heterogeneous. Herein, we report the identification a novel homozygous missense mutation, c.156 C > A in VPS16, co-segregating with disease status in a Chinese consanguineous family with adolescent-onset primary dystonia by whole exome sequencing and homozygosity mapping. To assess the biological role of c.156 C > A homozygous mutation of VPS16, we generated mice with targeted mutation site of Vps16 through CRISPR-Cas9 genome-editing approach. Vps16 c.156 C > A homozygous mutant mice exhibited significantly impaired motor function, suggesting that VPS16 is a new causative gene for adolescent-onset primary dystonia.

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Background: Several retinal dystrophies are associated with syndromic features including such conditions as Bardet-Biedl and Joubert syndromes. Cohen syndrome is an autosomal recessive disorder associated with multiple clinical manifestations including developmental delay, acquired microcephaly, myopia, pigmentary retinopathy, joint hypermobility, truncal obesity, friendly disposition and intermittent neutropenia. In young patients, diagnosis is difficult, because several of the characteristic features may not be present until school age or later years and the intermittent neutropenia is not always detectable.