A post-hoc comparison of the utility of sanger sequencing and exome sequencing for the diagnosis of heterogeneous diseases.

The advent of massive parallel sequencing is rapidly changing the strategies employed for the genetic diagnosis and research of rare diseases that involve a large number of genes. So far it is not clear whether these approaches perform significantly better than conventional single gene testing as requested by clinicians. The current yield of this traditional diagnostic approach depends on a complex of factors that include gene-specific phenotype traits, and the relative frequency of the involvement of specific genes. To gauge the impact of the paradigm shift that is occurring in molecular diagnostics, we assessed traditional Sanger-based sequencing (in 2011) and exome sequencing followed by targeted bioinformatics analysis (in 2012) for five different conditions that are highly heterogeneous, and for which our center provides molecular diagnosis. We find that exome sequencing has a much higher diagnostic yield than Sanger sequencing for deafness, blindness, mitochondrial disease, and movement disorders. For microsatellite-stable colorectal cancer, this was low under both strategies. Even if all genes that could have been ordered by physicians had been tested, the larger number of genes captured by the exome would still have led to a clearly superior diagnostic yield at a fraction of the cost.

Gene duplication and conversion events shaped three homologous, differentially expressed myosin regulatory light chain (MLC2) genes.

Myosin II is a hexameric protein complex consisting of two myosin heavy chains, two myosin essential light chains and two myosin regulatory light chains. Multiple subunit isoforms exist, allowing great diversity in myosin II composition which likely impacts on its contractile properties. Little is known about the evolutionary origin, expression pattern and function of myosin regulatory light chain (MLC2) isoforms. We analysed the evolutionary relationship between smooth muscle (sm), nonmuscle (nm) and nonmuscle-like (nml) MLC2 genes, which encode three homologous proteins expressed in nonmuscle cells. The three genes arose by successive gene duplication events. The high sequence similarity between the tandemly arranged nm- and nml-MLC2 genes is best explained by gene conversion. Urea/glycerol-polyacrylamide gel electrophoresis and RNA analysis were employed to monitor expression of sm-, nm- and nml-MLC2 in human and mouse cell lines. Conspicuous differences between transformed and non-transformed cells were observed, with sm-MLC2 being suppressed in Ras-transformed cells. Our findings shed light on the evolutionary history of three homologous MLC2 proteins and point to isoform-specific cell growth-related roles in nonmuscle cell myosin II contractility.