Applications and data analysis of next-generation sequencing

Over the past 6 years, next-generation sequencing (NGS) has been established as a valuable high-throughput method for research in molecular genetics and has successfully been employed in the identification of rare and common genetic variations. Although the high expectations regarding the discovery of new diagnostic targets and an overall reduction of cost have been achieved, technological challenges in instrument handling, robustness of the chemistry, and data analysis need to be overcome. Each workflow and sequencing platform have their particular problems and caveats, which need to be addressed. Regarding NGS, there is a variety of different enrichment methods, sequencing devices, or technologies as well as a multitude of analyzing software products available. In this manuscript, the authors focus on challenges in data analysis when employing different target enrichment methods and the best applications for each of the

Diagnostic applications of next generation sequencing: working towards quality standards

Over the past 6 years, next generation sequencing (NGS) has been established as a valuable high-throughput method for research in molecular genetics and has successfully been employed in the identification of rare and common genetic variations. All major NGS technology companies providing commercially available instruments (Roche 454, Illumina, Life Technologies) have recently marketed bench top sequencing instruments with lower throughput and shorter run times, thereby broadening the applications of NGS and opening the technology to the potential use for clinical diagnostics. Although the high expectations regarding the discovery of new diagnostic targets and an overall reduction of cost have been achieved, technological challenges in instrument handling, robustness of the chemistry and data analysis need to be overcome. To facilitate the implementation of NGS as a routine method in molecular diagnostics, consistent quality standards need to be developed. Here the authors give an overview of the current standards in protocols and workflows and discuss possible approaches to define quality criteria for NGS in molecular genetic diagnostics

Phosphorus Is Associated with Coronary Artery Disease in Patients with Preserved Renal Function

High serum phosphorus levels have been associated with mortality and cardiovascular events in patients with chronic kidney disease and in the general population. In addition, high phosphorus levels have been shown to induce vascular calcification and endothelial dysfunction in vitro. The aim of this study was to evaluate the relation of phosphorus and coronary calcification and atherosclerosis in the setting of normal renal function. This was a cross-sectional study involving 290 patients with suspected coronary artery disease and undergoing elective coronary angiography, with a creatinine clearance >60 ml/min/1.73 m2. Coronary artery obstruction was assessed by the Friesinger score and coronary artery calcification by multislice computed tomography. Serum phosphorus was higher in patients with an Agatston score >10 than in those with an Agatston score ≤10 (3.63±0.55 versus 3.49±0.52 mg/dl; p = 0.02). In the patients with Friesinger scores >4, serum phosphorus was higher (3.6±0.5 versus 3.5±0.6 mg/dl, p = 0.04) and median intact fibroblast growth factor 23 was lower (40.3 pg/ml versus 45.7 pg/ml, p = 0.01). Each 0.1-mg/dl higher serum phosphate was associated with a 7.4% higher odds of having a Friesinger score >4 (p = 0.03) and a 6.1% greater risk of having an Agatston score >10 (p = 0.01). Fibroblast growth factor 23 was a negative predictor of Friesinger score (p = 0.002). In conclusion, phosphorus is positively associated with coronary artery calcification and obstruction in patients with suspected coronary artery disease and preserved renal function

Hormone-like (endocrine) Fgfs: their evolutionary history and roles in development, metabolism, and disease

Fibroblast growth factors (Fgfs) are proteins with diverse functions in development, repair, and metabolism. The human Fgf gene family with 22 members can be classified into three groups, canonical, intracellular, and hormone-like Fgf genes. In contrast to canonical and intracellular Fgfs identified in invertebrates and vertebrates, hormone-like Fgfs, Fgf15/19, Fgf21, and Fgf23, are vertebrate-specific. The ancestral gene of hormone-like Fgfs was generated from the ancestral gene of canonical Fgfs by gene duplication early in vertebrate evolution. Later, Fgf15/19, Fgf21, and Fgf23 were generated from the ancestral gene by genome duplication events. Canonical Fgfs act as autocrine/paracrine factors in an Fgf receptor (Fgfr)-dependent manner. In contrast, hormone-like Fgfs act as endocrine factors in an Fgfr-dependent manner. Canonical Fgfs have a heparin-binding site necessary for the stable binding of Fgfrs and local signaling. In contrast, hormone-like Fgfs acquired endocrine functions by reducing their heparin-binding affinity during their evolution. Fgf15/19 and Fgf23 require βKlotho and αKlotho as cofactors, respectively. However, Fgf21 might physiologically require neither. Hormone-like Fgfs play roles in metabolism at postnatal stages, although they also play roles in development at embryonic stages. Fgf15/19 regulates bile acid metabolism in the liver. Fgf21 regulates lipid metabolism in the white adipose tissue. Fgf23 regulates serum phosphate and active vitamin D levels. Fgf23 signaling disorders caused by hereditary diseases or tumors result in metabolic disorders. In addition, serum Fgf19 or Fgf21 levels are significantly increased by metabolic disorders. Hormone-like Fgfs are newly emerging and quite unique in their evolution and function

CpG-Methylation Regulates a Class of Epstein-Barr Virus Promoters

DNA methylation is the major modification of eukaryotic genomes and plays an essential role in mammalian gene regulation. In general, cytosine-phosphatidyl-guanosine (CpG)-methylated promoters are transcriptionally repressed and nuclear proteins such as MECP2, MBD1, MBD2, and MBD4 bind CpG-methylated DNA and contribute to epigenetic silencing. Methylation of viral DNA also regulates gene expression of Epstein-Barr virus (EBV), which is a model of herpes virus latency. In latently infected human B cells, the viral DNA is CpG-methylated, the majority of viral genes is repressed and virus synthesis is therefore abrogated. EBV's BZLF1 encodes a transcription factor of the AP-1 family (Zta) and is the master gene to overcome viral gene repression. In a genome-wide screen, we now identify and characterize those viral genes, which Zta regulates. Among them are genes essential for EBV's lytic phase, which paradoxically depend on strictly CpG-methylated promoters for their Zta-induced expression. We identified novel DNA recognition motifs, termed meZRE (methyl-Zta-responsive element), which Zta selectively binds in order to ‘read’ DNA in a methylation- and sequence-dependent manner unlike any other known protein. Zta is a homodimer but its binding characteristics to meZREs suggest a sequential, non-palindromic and bipartite DNA recognition element, which confers superior DNA binding compared to CpG-free ZREs. Our findings indicate that Zta has evolved to transactivate cytosine-methylated, hence repressed, silent promoters as a rule to overcome epigenetic silencing

An FGF23 missense mutation causes familial tumoral calcinosis with hyperphosphatemia.

Familial tumoral calcinosis (FTC) is an autosomal recessive disorder characterized by ectopic calcifications and elevated serum phosphate levels. Recently, mutations in the GALNT3 gene have been described to cause FTC. The FTC phenotype is regarded as the metabolic mirror image of hypophosphatemic conditions, where causal mutations are known in genes FGF23 or PHEX. We investigated an individual with FTC who was negative for GALNT3 mutations. Sequencing revealed a homozygous missense mutation in the FGF23 gene (p.S71G) at an amino acid position which is conserved from fish to man. Wild-type FGF23 is secreted as intact protein and processed N-terminal and C-terminal fragments. Expression of the mutated protein in HEK293 cells showed that only the C-terminal fragment is secreted, whereas the intact protein is retained in the Golgi complex. In addition, determination of circulating FGF23 in the affected individual showed a marked increase in the C-terminal fragment. These results suggest that the FGF23 function is decreased by absent or extremely reduced secretion of intact FGF23. We conclude that FGF23 mutations in hypophosphatemic rickets and FTC have opposite effects on phosphate homeostasis

A gene locus responsible for the familial hair shaft abnormality pili annulati maps to chromosome 12q24.32-24.33.

Pili annulati, a rare hair shaft abnormality with a characteristic shiny appearance due to alternating light and dark bands of the hair, is assumed to be inherited in an autosomal dominant mode with high penetrance. A locus for pili annulati has not been found yet. We identified one large and four small European kindreds with pili annulati and conducted a genomewide linkage analysis using 382 microsatellite markers. A multipoint logarithm of the odds (LOD) score of 3.19 was demonstrated between D12S1659 and D12S1723 on the telomeric part of the long arm of chromosome 12. Subsequent finemapping in a region of 20 cM gave a maximum multipoint LOD score of 3.24 at D12S1723 under the assumption of homogeneity and a LOD score of 3.57 around D12S343 under the assumption of heterogeneity, both exceed the statistical thresholds necessary to conclude linkage. Most of this LOD score came from the largest family, which reached a maximum LOD score of 3.81. The maximum two-point LOD score for all families was 3.97 at D12S1609. Definite recombination events narrowed the region of shared haplotype in the affected individuals to an 8 Mb region between the marker D12S324 and the telomeric end of the long arm of chromosome 12

Polypeptide GaINAc-transferase T3 and familial tumoral calcinosis.

Mutations in the gene encoding the glycosyltransferase polypeptide GalNAc-T3, which is involved in initiation of O-glycosylation, were recently identified as a cause of the rare autosomal recessive metabolic disorder familial tumoral calcinosis (OMIM 211900). Familial tumoral calcinosis is associated with hyperphosphatemia and massive ectopic calcifications. Here, we demonstrate that the secretion of the phosphaturic factor fibroblast growth factor 23 (FGF23) requires O-glycosylation, and that GalNAc-T3 selectively directs O-glycosylation in a subtilisin-like proprotein convertase recognition sequence motif, which blocks processing of FGF23. The study suggests a novel posttranslational regulatory model of FGF23 involving competing O-glycosylation and protease processing to produce intact FGF23