Novel POC1A mutation in primordial dwarfism reveals new insights for centriole biogenesis.

POC1A encodes a WD repeat protein localizing to centrioles and spindle poles and is associated with short stature, onychodysplasia, facial dysmorphism and hypotrichosis (SOFT) syndrome. These main features are related to the defect in cell proliferation of chondrocytes in growth plate. In the current study, we aimed at identifying the molecular basis of two patients with primordial dwarfism (PD) in a single family through utilization of whole-exome sequencing. A novel homozygous p.T120A missense mutation was detected in POC1A in both patients, a known causative gene of SOFT syndrome, and confirmed using Sanger sequencing. To test the pathogenicity of the detected mutation, primary fibroblast cultures obtained from the patients and a control individual were used. For evaluating the global gene expression profile of cells carrying p.T120A mutation in POC1A, we performed the gene expression array and compared their expression profiles to those of control fibroblast cells. The gene expression array analysis showed that 4800 transcript probes were significantly deregulated in cells with p.T120A mutation in comparison to the control. GO term association results showed that deregulated genes are mostly involved in the extracellular matrix and cytoskeleton. Furthermore, the p.T120A missense mutation in POC1A caused the formation of abnormal mitotic spindle structure, including supernumerary centrosomes, and changes in POC1A were accompanied by alterations in another centrosome-associated WD repeat protein p80-katanin. As a result, we identified a novel mutation in POC1A of patients with PD and showed that this mutation causes the formation of multiple numbers of centrioles and multipolar spindles with abnormal chromosome arrangement.

Early postzygotic mutations contribute to de novo variation in a healthy monozygotic twin pair.

BACKGROUND: Human de novo single-nucleotide variation (SNV) rate is estimated to range between 0.82-1.70×10(-8) mutations per base per generation. However, contribution of early postzygotic mutations to the overall human de novo SNV rate is unknown. METHODS: We performed deep whole-genome sequencing (more than 30-fold coverage per individual) of the whole-blood-derived DNA samples of a healthy monozygotic twin pair and their parents. We examined the genotypes of each individual simultaneously for each of the SNVs and discovered de novo SNVs regarding the timing of mutagenesis. Putative de novo SNVs were validated using Sanger-based capillary sequencing. RESULTS: We conservatively characterised 23 de novo SNVs shared by the twin pair, 8 de novo SNVs specific to twin I and 1 de novo SNV specific to twin II. Based on the number of de novo SNVs validated by Sanger sequencing and the number of callable bases of each twin, we calculated the overall de novo SNV rate of 1.31×10(-8) and 1.01×10(-8) for twin I and twin II, respectively. Of these, rates of the early postzygotic de novo SNVs were estimated to be 0.34×10(-8) for twin I and 0.04×10(-8) for twin II. CONCLUSIONS: Early postzygotic mutations constitute a substantial proportion of de novo mutations in humans. Therefore, genome mosaicism resulting from early mitotic events during embryogenesis is common and could substantially contribute to the development of diseases.

A probable new syndrome with the storage disease phenotype caused by the VPS33A gene mutation.

We present a novel multisystem disease in two siblings with clinical features resembling a lysosomal storage disease. These included coarse face, dysostosis multiplex, respiratory difficulty, proteinuria with glomerular foamy cells, neurological involvement with developmental delays, pyramidal signs, and severe chronic anemia. Detailed enzymatic analysis for lysosomal diseases and whole-exome sequencing studies excluded known lysosomal storage diseases in the proband. Subsequently, genome-wide genotyping and exome sequencing analysis of the family indicated two large homozygous regions on chromosomes 5 and 12, and strongly suggested that a homozygous p. R498W missense mutation in the VPS33A gene might be responsible for this novel disease. Segregation analysis in family members and mutation prediction tools' results also supported the damaging effect of the missense mutation on the function of the Vps33a protein, which plays a role in the vesicular transport system. Electron microscopic studies of the cornea of the proband showed findings supportive of dysfunction in vesicular transport. The clinical phenotype and genetic studies support the suggestion that the siblings most probably have a novel disease very likely caused by a VPS33A gene defect.

Myophosphorylase (PYGM) mutations determined by next generation sequencing in a cohort from Turkey with McArdle disease.

This study aimed to identify PYGM mutations in patients with McArdle disease from Turkey by next generation sequencing (NGS). Genomic DNA was extracted from the blood of the McArdle patients (n = 67) and unrelated healthy volunteers (n = 53). The PYGM gene was sequenced with NGS and the observed mutations were validated by direct Sanger sequencing. A diagnostic algorithm was developed for patients with suspected McArdle disease. A total of 16 deleterious PYGM mutations were identified, of which 5 were novel, including 1 splice-site donor, 1 frame-shift, and 3 non-synonymous variants. The p.Met1Val (27-patients/11-families) was the most common PYGM mutation, followed by p.Arg576* (6/4), c.1827+7A>G (5/4), c.772+2_3delTG (5/3), p.Phe710del (4/2), p.Lys754Asnfs (2/1), and p.Arg50* (1/1). A molecular diagnostic flowchart is proposed for the McArdle patients in Turkey, covering the 6 most common PYGM mutations found in Turkey as well as the most common mutation in Europe. The diagnostic algorithm may alleviate the need for muscle biopsies in 77.6% of future patients. A prevalence of any of the mutations to a geographical region in Turkey was not identified. Furthermore, the NGS approach to sequence the entire PYGM gene was successful in detecting a common missense mutation and discovering novel mutations in this population study.

Performance comparison of Next Generation sequencing platforms.

Next Generation DNA Sequencing technologies offer ultra high sequencing throughput for very low prices. The increase in throughput and diminished costs open up new research areas. Moreover, number of clinicians utilizing DNA sequencing keeps growing. One of the main concern for researchers and clinicians who are adopting these platforms is their sequencing accuracy. We compared three of the most commonly used Next Generation Sequencing platforms; Ion Torrent from Life Technologies, GS FLX+ from Roche and HiSeq 2000 from Illumina.

A clinical variant in SCN1A inherited from a mosaic father cosegregates with a novel variant to cause Dravet syndrome in a consanguineous family.

A consanguineous family from Turkey having two children with intellectual disability exhibiting myoclonic, febrile and other generalized seizures was recruited to identify the genetic origin of these phenotypes. A combined approach of SNP genotyping and exome sequencing was employed both to screen genes associated with Dravet syndrome and to detect homozygous variants. Analysis of exome data was extended further to identify compound heterozygosity. Herein, we report identification of two paternally inherited genetic variants in SCN1A (rs121917918; p.R101Q and p.I1576T), one of which was previously implicated in Dravet syndrome. Interestingly, the previously reported clinical variant (rs121917918; p.R101Q) displayed mosaicism in the blood and saliva of the father. The study supported the genetic diagnosis of affected children as Dravet syndrome possibly due to the combined effect of one clinically associated (rs121917918; p.R101Q) and one novel (p.I1576T) variants in SCN1A gene. This finding is important given that heterozygous variants may be overlooked in standard exome scans of consanguineous families. Thus, we are presenting an interesting example, where the inheritance of the condition may be misinterpreted as recessive and identical by descent due to consanguinity and mosaicism in one of the parents.