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Pathogenic variants in the PJVK gene cause the DFNB59 type of autosomal recessive non-syndromic hearing impairment (AR-NSHI). Phenotypes are not homogeneous, as a few subjects show auditory neuropathy spectrum disorder (ANSD), while others show cochlear hearing loss. The numbers of reported cases and pathogenic variants are still small to establish accurate genotype-phenotype correlations. We investigated a cohort of 77 Spanish familial cases of AR-NSHI, in whom DFNB1 had been excluded, and a cohort of 84 simplex cases with isolated ANSD in whom OTOF variants had been excluded. All seven exons and exon-intron boundaries of the PJVK gene were sequenced. We report three novel DFNB59 cases, one from the AR-NSHI cohort and two from the ANSD cohort, with stable, severe to profound NSHI. Two of the subjects received unilateral cochlear implantation, with apparent good outcomes. Our study expands the spectrum of PJVK mutations, as we report four novel pathogenic variants: p.Leu224Arg, p.His294Ilefs*43, p.His294Asp and p.Phe317Serfs*20. We review the reported cases of DFNB59, summarize the clinical features of this rare subtype of AR-NSHI and discuss the involvement of PJVK in ANSD.

Pathogenic variants in the PJVK gene cause the DFNB59 type of autosomal recessive non-syndromic hearing impairment (AR-NSHI). Phenotypes are not homogeneous, as a few subjects show auditory neuropathy spectrum disorder (ANSD), while others show cochlear hearing loss. The numbers of reported cases and pathogenic variants are still small to establish accurate genotype-phenotype correlations. We investigated a cohort of 77 Spanish familial cases of AR-NSHI, in whom DFNB1 had been excluded, and a cohort of 84 simplex cases with isolated ANSD in whom OTOF variants had been excluded. All seven exons and exon-intron boundaries of the PJVK gene were sequenced. We report three novel DFNB59 cases, one from the AR-NSHI cohort and two from the ANSD cohort, with stable, severe to profound NSHI. Two of the subjects received unilateral cochlear implantation, with apparent good outcomes. Our study expands the spectrum of PJVK mutations, as we report four novel pathogenic variants: p.Leu224Arg, p.His294Ilefs*43, p.His294Asp and p.Phe317Serfs*20. We review the reported cases of DFNB59, summarize the clinical features of this rare subtype of AR-NSHI and discuss the involvement of PJVK in ANSD.

PRPS1 encodes isoform I of phosphoribosylpyrophosphate synthetase (PRS-I), a key enzyme in nucleotide biosynthesis. Different missense mutations in PRPS1 cause a variety of disorders that include PRS-I superactivity, nonsyndromic sensorineural hearing impairment, Charcot-Marie-Tooth disease, and Arts syndrome. It has been proposed that each mutation would result in a specific phenotype, depending on its effects on the structure and function of the enzyme.Thirteen Spanish unrelated families segregating X-linked hearing impairment were screened for PRPS1 mutations by Sanger sequencing. In two positive pedigrees, segregation of mutations was studied, and clinical data from affected subjects were compared.We report two novel missense mutations in PRPS1, p.Ile275Thr and p.Gly306Glu, which were found in the propositi of two unrelated Spanish families, both subjects presenting with nonsyndromic hearing impairment. Further investigation revealed syndromic features in other hemizygous carriers from one of the pedigrees. Sequencing of genes that are functionally related to PRPS1 did not reveal any candidate variant that might act as a phenotype modifier.This case of intrafamilial phenotypic variation associated with a single PRPS1 mutation complicates the genotype-phenotype correlations, which makes genetic counseling of mutation carriers difficult because of the wide spectrum of severity of the associated disorders.

DOOFNL Consortium., In a Dutch consanguineous family with recessively inherited nonsyndromic hearing impairment (HI), homozygosity mapping combined with whole-exome sequencing revealed a MPZL2 homozygous truncating variant, c.72del (p.Ile24Metfs∗22). By screening a cohort of phenotype-matched subjects and a cohort of HI subjects in whom WES had been performed previously, we identified two additional families with biallelic truncating variants of MPZL2. Affected individuals demonstrated symmetric, progressive, mild to moderate sensorineural HI. Onset of HI was in the first decade, and high-frequency hearing was more severely affected. There was no vestibular involvement. MPZL2 encodes myelin protein zero-like 2, an adhesion molecule that mediates epithelial cell-cell interactions in several (developing) tissues. Involvement of MPZL2 in hearing was confirmed by audiometric evaluation of Mpzl2-mutant mice. These displayed early-onset progressive sensorineural HI that was more pronounced in the high frequencies. Histological analysis of adult mutant mice demonstrated an altered organization of outer hair cells and supporting cells and degeneration of the organ of Corti. In addition, we observed mild degeneration of spiral ganglion neurons, and this degeneration was most pronounced at the cochlear base. Although MPZL2 is known to function in cell adhesion in several tissues, no phenotypes other than HI were found to be associated with MPZL2 defects. This indicates that MPZL2 has a unique function in the inner ear. The present study suggests that deleterious variants of Mplz2/MPZL2 affect adhesion of the inner-ear epithelium and result in loss of structural integrity of the organ of Corti and progressive degeneration of hair cells, supporting cells, and spiral ganglion neurons., This work was supported by a grant from the Heinsius Houbolt Foundation (to H.K., R.J.E.P., and H.P.M.K.) and partially by grants from the Spanish Ministry of Economy and Competitiveness and the European Regional Development Fund (Fonds Europeen de Developpement Economique et Regional, [FEDER]: SAF2014-53979-R) and from FEDER, CIBERER, and Instituto de Salud Carlos III (ISCIII) (to I.V.N.), and a grant from ISCIII to I.d.C. (PI14/01162; Plan Estatal de IþDþI 2013-2016, with co-funding from the European Regional Development Fund). S.M., A.M.C., and E.G.R. hold CIBERER ISCIII researcher contracts.

Autosomal recessive nonsyndromic hearing impairment (NSHI) is a heterogeneous condition, for which 53 genetic loci have been reported, and 29 genes have been identified to date. One of these, OTOF, encodes otoferlin, a membrane-anchored calcium-binding protein that plays a role in the exocytosis of synaptic vesicles at the auditory inner hair cell ribbon synapse. We have investigated the prevalence and spectrum of deafness-causing mutations in the OTOF gene. Cohorts of 708 Spanish, 83 Colombian, and 30 Argentinean unrelated subjects with autosomal recessive NSHI were screened for the common p.Gln829X mutation. In compound heterozygotes, the second mutant allele was identified by DNA sequencing. In total, 23 Spanish, two Colombian and two Argentinean subjects were shown to carry two mutant alleles of OTOF. Of these, one Colombian and 13 Spanish subjects presented with auditory neuropathy. In addition, a cohort of 20 unrelated subjects with a diagnosis of auditory neuropathy, from several countries, was screened for mutations in OTOF by DNA sequencing. A total of 11 of these subjects were shown to carry two mutant alleles of OTOF. In total, 18 pathogenic and four neutral novel alleles of the OTOF gene were identified. Haplotype analysis for markers close to OTOF suggests a common founder for the novel c.2905_2923delinsCTCCGAGCGCA mutation, frequently found in Argentina. Our results confirm that mutation of the OTOF gene correlates with a phenotype of prelingual, profound NSHI, and indicate that OTOF mutations are a major cause of inherited auditory neuropathy. Hum Mutat 29(6), 823–831, 2008. © 2008 Wiley-Liss, Inc.

Background The Synovitis, Acne, Pustulosis, Hyperostosis and Osteitis (SAPHO) syndrome is currently considered as an autoinflammatory disorder of bone and skin that can be classified with the inflammatory spondyloarthropathies (1). Genetic predisposing factors for SAPHO syndrome have been long suspected because of reported familial clustering of the syndrome, although most cases are sporadic (2). Additional support for a genetic origin of the syndrome is provided by a murine model (the cmo mouse) that carries a spontaneous recessive mutation in the Pstpip2 gene (3). However, previous studies excluded a role for the genes PSIPT2 , LPIN and NOD2 in the pathogenesis of the syndrome (4). Two rare autoinflammatory disorders, DIRA and DITRA syndromes, have been related to a genetic deficiency in interleukin-1 (IL-1) and IL-36 receptor antagonists, respectively (5-7). These two conditions, particularly DIRA syndrome, share some features with SAPHO syndrome. Objectives We investigated the possible role of the genes encoding IL-1 receptor antagonist ( IL1RN ), IL-36 receptor ( IL36R ), IL-36 receptor antagonist ( IL36RN ) and cell-surface lectin Siglec-15 ( SIGLEC15 ) in the pathogenesis of SAPHO syndrome. Methods The study was performed on a cohort of 40 SAPHO syndrome subjects that includes 3 familial cases. After obtaining written informed consent, we extracted DNA from peripheral blood samples by using automated magnetic-bead technology (Chemagen). We PCR-amplified and sequenced all exons and intron-exon boundaries of the four candidate genes. In addition, we carried out a genome-wide copy-number variation (CNV) analysis on SNP arrays (Illumina BeadStudio array of 2.5 million SNPs). Results We did not identify any pathogenic mutations in the IL1RN , IL36R , IL36RN and SIGLEC15 genes, although we did detect known polymorphic variations. Heterozygosity and CNV analyses excluded any deletions of the candidate genes in our cohort. Conclusions We found no involvement of the IL1RN , IL36R , IL36RN and SIGLEC15 genes in the pathogenesis of SAPHO syndrome. References Clin Exp Rheumatol 1988; 6 : 109-112. Joint Bone Spine 2007; 74 : 123-126. Bone 2006; 38 : 41-47. J Rheumatol 2010; 37 : 401-409. N Engl J Med 2009; 360 : 2426-2437. N Engl J Med 2011; 365 :620–628. Am J Hum Genet 2011; 89 : 432–437. Acknowledgements T.C. was a recipient of an “Ayuda Predoctoral” fellowship from CIBERER. This work was supported by grant FIS PI11/00283 from ISCIII (to F.J.d.C.). Disclosure of Interest None Declared