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The expanding spectrum of PRPS1-associated phenotypes: three novel mutations segregating with X-linked hearing loss and mild peripheral neuropathy.

ABSTRACT: Next-generation sequencing is currently the technology of choice for gene/mutation discovery in genetically-heterogeneous disorders, such as inherited sensorineural hearing loss (HL). Whole-exome sequencing of a single Italian proband affected by non-syndromic HL identified a novel missense variant within the PRPS1 gene (NM_002764.3:c.337G>T (p.A113S)) segregating with post-lingual, bilateral, progressive deafness in the proband's family. Defects in this gene, encoding the phosphoribosyl pyrophosphate synthetase 1 (PRS-I) enzyme, determine either X-linked syndromic conditions associated with hearing impairment (eg, Arts syndrome and Charcot-Marie-Tooth neuropathy type X-5) or non-syndromic HL (DFNX1). A subsequent screening of the entire PRPS1 gene in 16 unrelated probands from X-linked deaf families led to the discovery of two additional missense variants (c.343A>G (p.M115V) and c.925G>T (p.V309F)) segregating with hearing impairment, and associated with mildly-symptomatic peripheral neuropathy. All three variants result in a marked reduction (>60%) of the PRS-I activity in the patients' erythrocytes, with c.343A>G (p.M115V) and c.925G>T (p.V309F) affecting more severely the enzyme function. Our data significantly expand the current spectrum of pathogenic variants in PRPS1, confirming that they are associated with a continuum disease spectrum, thus stressing the importance of functional studies and detailed clinical investigations for genotype-phenotype correlation.

SUBMITTER: Robusto M

PROVIDER: S-EPMC4270732 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Phosphoribosyl 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.Whole 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.A 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.These 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.

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The expanding spectrum of PRPS1-associated phenotypes: three novel mutations segregating with X-linked hearing loss and mild peripheral neuropathy.

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