We have identified common CF causing mutations in the Hungarian population with the most common mutations (p.Phe508del, p.Asn1303Lys, CFTRdele2,3(21kb), 2184insA, p.Gly542X, and p.Leu101X), comprising over 93.75% of all CF alleles. Obtained data are applicable to the improvement of DNA diagnostics in Hungary and beyond, and are the necessary prerequisite for the introduction of a nationwide "two tier" CF newborn screening program.
We found all ARPKD cases without PKHD1 point mutations to be phenocopies, and none to be explained by biallelic PKHD1 copy number variations. Screening for copy number variations is recommended in patients with a heterozygous point mutation.
BackgroundCurrent technologies in next-generation sequencing are offering high throughput reads at low costs, but still suffer from various sequencing errors. Although pyro- and ion semiconductor sequencing both have the advantage of delivering long and high quality reads, problems might occur when sequencing homopolymer-containing regions, since the repeating identical bases are going to incorporate during the same synthesis cycle, which leads to uncertainty in base calling. The aim of this study was to evaluate the analytical performance of a pyrosequencing-based next-generation sequencing system in detecting homopolymer sequences using homopolymer-preintegrated plasmid constructs and human DNA samples originating from patients with cystic fibrosis.ResultsIn the plasmid system average correct genotyping was 95.8% in 4-mers, 87.4% in 5-mers and 72.1% in 6-mers. Despite the experienced low genotyping accuracy in 5- and 6-mers, it was possible to generate amplicons with more than a 90% adequate detection rate in every homopolymer tract. When homopolymers in the CFTR gene were sequenced average accuracy was 89.3%, but varied in a wide range (52.2 – 99.1%). In all but one case, an optimal amplicon-sequencing primer combination could be identified. In that single case (7A tract in exon 14 (c.2046_2052)), none of the tested primer sets produced the required analytical performance.ConclusionsOur results show that pyrosequencing is the most reliable in case of 4-mers and as homopolymer length gradually increases, accuracy deteriorates. With careful primer selection, the NGS system was able to correctly genotype all but one of the homopolymers in the CFTR gene. In conclusion, we configured a plasmid test system that can be used to assess genotyping accuracy of NGS devices and developed an accurate NGS assay for the molecular diagnosis of CF using self-designed primers for amplification and sequencing.Electronic supplementary materialThe online version of this article (10.1186/s12864-018-4544-x) contains supplementary material, which is available to authorized users.
Cerebrotendinous xanthomatosis (CTX) is a rare, genetically determined error of metabolism. The characteristic clinical symptoms are diarrhea, juvenile cataracts, tendon xanthomas and neuropsychiatric alterations. The aim of this study is to present a pair of identical adult twins with considerable differences in the severity of phenotype. With regards to neuropsychiatric symptoms, the predominant features were severe Parkinsonism and moderate cognitive dysfunctions in the more-affected individual, whereas these alterations in the less-affected patient were only very mild and mild, respectively. The characteristic increase in the concentrations of serum cholestanol and the lesion volumes in dentate nuclei in the brain assessed with magnetic resonance imaging were quite similar in both cases. The lifestyle conditions, including eating habits of the twin pair, were quite similar as well; therefore, currently unknown genetic modifiers or certain epigenetic factors may be responsible for the differences in severity of phenotype. This case series serves as the first description of an identical twin pair with CTX presenting heterogeneous clinical features.
SummaryBackgroundIn this study the authors present an update to the CFTR mutation profile in Hungary, utilizing data from a selected cohort of 45 cystic fibrosis (CF) patients from different regions of the country.MethodsDepending on the preceding analysis, four different mutation detection methods were used. A commercial assay targeting the most common CF-causing mutations was performed as the first test followed by an allele specific PCR for CFTRdele2,3(21kb), Sanger sequencing and MLPA analysis of the coding region of the CFTR gene.ResultsIn our recent study 27 different mutations were detected, including 2 novel ones (c.1037_1038insA and c.1394C>T). Besides F508del (c.1521_1523delCTT), the following mutations were found at a frequency of ≥ 4.0%: W1282X (c.3846G>A), N1303K (c.3909C>G), CFTRdele2,3(21kb) (c.54-5940_273+10250del21kb) and 2184insA (c.2052_2053insA). In addition, four mutations (G542X, Y1092X, 621+1G>T, and 2143delT) were found in more than one allele.ConclusionsThe updated database of Hungarian mutations not only enables to increase the efficiency of the existing diagnostic approach, but also provides a further refined basis for the introduction of the molecular newborn screening (NBS) program in Hungary.
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