Identification and in vivo functional investigation of a HOMER2 nonstop variant causing hearing loss.

DFNA68 is a rare subtype of autosomal dominant nonsyndromic hearing impairment caused by heterozygous alterations in the HOMER2 gene. To date, only 5 pathogenic or likely pathogenic coding variants, including two missense substitutions (c.188 C > T and c.587 G > C), a single base pair duplication (c.840dupC) and two short deletions (c.592_597delACCACA and c.832_836delCCTCA) have been described in 5 families. In this study, we report a novel HOMER2 variation, identified by massively parallel sequencing, in a Sicilian family suffering from progressive dominant hearing loss over 3 generations. This novel alteration is a nonstop substitution (c.1064 A > G) that converts the translational termination codon (TAG) of the gene into a tryptophan codon (TGG) and is predicted to extend the HOMER2 protein by 10 amino acids. RNA analyses from the proband suggested that HOMER2 transcripts carrying the nonstop variant escaped the non-stop decay pathway. Finally, in vivo studies using a zebrafish animal model and behavioral tests clearly established the deleterious impact of this novel HOMER2 alteration on hearing function. This study identifies the fourth causal variation responsible for DFNA68 and describes a simple in vivo approach to assess the pathogenicity of candidate HOMER2 variants.

The Study of a 231 French Patient Cohort Significantly Extends the Mutational Spectrum of the Two Major Usher Genes MYO7A and USH2A.

Usher syndrome is an autosomal recessive disorder characterized by congenital hearing loss combined with retinitis pigmentosa, and in some cases, vestibular areflexia. Three clinical subtypes are distinguished, and MYO7A and USH2A represent the two major causal genes involved in Usher type I, the most severe form, and type II, the most frequent form, respectively. Massively parallel sequencing was performed on a cohort of patients in the context of a molecular diagnosis to confirm clinical suspicion of Usher syndrome. We report here 231 pathogenic MYO7A and USH2A genotypes identified in 73 Usher type I and 158 Usher type II patients. Furthermore, we present the ACMG classification of the variants, which comprise all types. Among them, 68 have not been previously reported in the literature, including 12 missense and 16 splice variants. We also report a new deep intronic variant in USH2A. Despite the important number of molecular studies published on these two genes, we show that during the course of routine genetic diagnosis, undescribed variants continue to be identified at a high rate. This is particularly pertinent in the current era, where therapeutic strategies based on DNA or RNA technologies are being developed.

Assessment of the latest NGS enrichment capture methods in clinical context.

Enrichment capture methods for NGS are widely used, however, they evolve rapidly and it is necessary to periodically measure their strengths and weaknesses before transfer to diagnostic services. We assessed two recently released custom DNA solution-capture enrichment methods for NGS, namely Illumina NRCCE and Agilent SureSelect(QXT), against a reference method NimbleGen SeqCap EZ Choice on a similar gene panel, sharing 678 kb and 110 genes. Two Illumina MiSeq runs of 12 samples each have been performed, for each of the three methods, using the same 24 patients (affected with sensorineural disorders). Technical outcomes have been computed and compared, including depth and evenness of coverage, enrichment in targeted regions, performance in GC-rich regions and ability to generate consistent variant datasets. While we show that the three methods resulted in suitable datasets for standard DNA variant discovery, we describe significant differences between the results for the above parameters. NimbleGen offered the best depth of coverage and evenness, while NRCCE showed the highest on target levels but high duplicate rates. SureSelect(QXT) showed an overall quality close to that of NimbleGen. The new methods exhibit reduced preparation time but behave differently. These findings will guide laboratories in their choice of library enrichment approach.