The molecular spectrum and clinical impact of DIS3 mutations in multiple myeloma.

Multiple myeloma (MM) is a plasma cell neoplasm that presents with a major biological and clinical heterogeneity. We here investigated the spectrum of clonal and subclonal mutations of DIS3, an active part of the exosome complex, that may play a role in the development or progression of MM. The whole coding sequence of DIS3 was subjected to deep sequencing in 81 uniformly-treated MM patients and 12 MM cell lines and the overall occurrence of DIS3 mutations as well as the presence of DIS3 mutations in minor and major subclones were correlated with cytogenetic alterations and clinical parameters. Our study identified DIS3 mutations in 9/81 patients that were associated with 13q14 deletions and IGH translocations on the cytogenetic level. Specifically, we detected seven novel somatic DIS3 single nucleotide variants (SNVs) and defined three hot spot mutations within the RNB domain. Lastly, we found a trend towards a shorter median overall survival for patients with DIS3 mutations, and patients carrying DIS3 mutations in minor subclones of their tumours showed a significantly worse response to therapy compared to patients with DIS3 mutations in the major subclone.

Novel recessive myotilin mutation causes severe myofibrillar myopathy.

We identified the first homozygous and hence recessive mutation in the myotilin gene (MYOT) in a family affected by a severe myofibrillar myopathy (MFM). MFM is a rare, progressive and devastating disease of human skeletal muscle with distinct histopathological pattern of protein aggregates and myofibrillar degeneration. So far, only heterozygous missense mutations in MYOT have been associated with autosomal dominant myofibrillar myopathy, limb-girdle muscular dystrophy type 1A and distal myopathy. Myotilin itself is highly expressed in skeletal and cardiac muscle and is localized at the Z-disc and therefore interacts in sarcomere assembly. We performed whole-exome sequencing in a German family clinically diagnosed with MFM and identified a homozygous mutation in exon 2, c.16C > G (p.Arg6Gly). Using laser microdissection followed by quantitative mass spectrometry, we identified the myotilin protein as one component showing the highest increased abundance in the aggregates in the index patient. We suggest that the combined approach has a high potential as a new tool for the confirmation of unclassified variants which are found in whole-exome sequencing approaches.

Novel form of X-linked nonsyndromic hearing loss with cochlear malformation caused by a mutation in the type IV collagen gene COL4A6.

Hereditary hearing loss is the most common human sensorineural disorder. Genetic causes are highly heterogeneous, with mutations detected in >40 genes associated with nonsyndromic hearing loss, to date. Whereas autosomal recessive and autosomal dominant inheritance is prevalent, X-linked forms of nonsyndromic hearing impairment are extremely rare. Here, we present a Hungarian three-generation family with X-linked nonsyndromic congenital hearing loss and the underlying genetic defect. Next-generation sequencing and subsequent segregation analysis detected a missense mutation (c.1771G>A, p.Gly591Ser) in the type IV collagen gene COL4A6 in all affected family members. Bioinformatic analysis and expression studies support this substitution as being causative. COL4A6 encodes the alpha-6 chain of type IV collagen of basal membranes, which forms a heterotrimer with two alpha-5 chains encoded by COL4A5. Whereas mutations in COL4A5 and contiguous X-chromosomal deletions involving COL4A5 and COL4A6 are associated with X-linked Alport syndrome, a nephropathy associated with deafness and cataract, mutations in COL4A6 alone have not been related to any hereditary disease so far. Moreover, our index patient and other affected family members show normal renal and ocular function, which is not consistent with Alport syndrome, but with a nonsyndromic type of hearing loss. In situ hybridization and immunostaining demonstrated expression of the COL4A6 homologs in the otic vesicle of the zebrafish and in the murine inner ear, supporting its role in normal ear development and function. In conclusion, our results suggest COL4A6 as being the fourth gene associated with X-linked nonsyndromic hearing loss.