Ethnically unique disease burden and limitations of current expanded carrier screening panels.

OBJECTIVES: The purpose of the study is to identify the recessive diseases currently affecting real-world pediatric patients in Taiwan, and whether current extended carrier screening panels have the coverage and detective power to identify the pathogenic variants in the carrier parents. METHODS: A total of 132 trio-samples were collected from May 2017 to March 2022. The participants were parents of pediatric intensive care unit patients who were critically ill or infants with abnormal newborn screening results. A retrospective carrier screening scheme was applied to analyze only the carrier status of pathogenic or likely pathogenic recessive variants resulting in diseases in their children. The recessive disorders diagnosed in our cohort were compared with the gene content in commercial panels. RESULTS: Mutations in COQ4, PEX1, OTC, and IKBKG were the most frequently identified. In the parents of 44 children with confirmed diagnoses of recessive diseases, 47 (53.40%) screened positive for being the carriers of the same recessive disorders diagnosed in their children. The commercial panels covered 35.13% to 54.05% of the disorders diagnosed in this cohort. CONCLUSION: Clinicians and genetic counselors should be aware of the limitations of current extended carrier screening and interpret negative screening results with caution. Future panels should also consider genes with ethnically unique mutations such as pathogenic variants of the COQ4 gene in the East Asian population.

Curated incidence of lysosomal storage diseases from the Taiwan Biobank.

Lysosomal storage diseases (LSDs) are a group of metabolic disorders resulting from a deficiency in one of the lysosomal hydrolases. Most LSDs are inherited in an autosomal or X-linked recessive manner. As LSDs are rare, their true incidence in Taiwan remains unknown. In this study, we used high-coverage whole-genome sequencing data from 1,495 Taiwanese individuals obtained from the Taiwan Biobank. We found 3826 variants in 71 genes responsible for autosomal recessive LSDs. We first excluded benign variants by allele frequency and other criteria. As a result, 270 variants were considered disease-causing. We curated these variants using published guidelines from the American College of Medical Genetics and Genomics (ACMG). Our results revealed a combined incidence rate of 13 per 100,000 (conservative estimation by pathologic and likely pathogenic variants; 95% CI 6.92-22.23) to 94 per 100,000 (extended estimation by the inclusion of variants of unknown significance; 95% CI 75.96-115.03) among 71 autosomal recessive disease-associated genes. The conservative estimations were similar to those in published clinical data. No disease-causing mutations were found for 18 other diseases; thus, these diseases are likely extremely rare in Taiwan. The study results are important for designing screening and treatment methods for LSDs in Taiwan and demonstrate the importance of mutation curation to avoid overestimating disease incidences from genomic data.

Utility of whole-exome sequencing for patients with multiple congenital anomalies with or without intellectual disability/developmental delay in East Asia population.

BACKGROUND: Congenital anomalies (CAs) with or without intellectual disability (ID)/developmental delay (DD) comprise a heterogeneous spectrum of diseases that affect approximately 3% of live births worldwide. Recently, whole-exome sequencing (WES) demonstrated the highly heterogeneous genetic causes of CAs. The purpose of this study was to evaluate a referral system to increase the yield of WES for CAs. METHODS: From August 2018 to July 2019, patients with CAs, with or without ID/DD, after excluding gross chromosomal aberrations, were referred to geneticists in two medical centers. Variant prioritization was conducted with an AI-assisted tool for whole exomes or a CA-related gene panel. RESULTS: Forty patients (27 males and 13 females) with CAs were enrolled in the study with a mean age of 4.71 years (range, 0.01-18.2). Pathogenic variants in 14 genes were discovered in 16 patients (three patients with CHD7 and 13 patients with one gene each of ATP6V1B2, TAF6, COL4A3BP, ANKH, BMP2, SMARCA4, CUL4B, PGAP3, SOX11, FBN2, PTPN11, SOS1, or PROKR2), with a positive diagnostic rate of 40%. Among the 16 positive cases, 13 (81%) also had ID/DD. The inheritance was autosomal dominant in 13 (81%), autosomal recessive in two (13%), and X-linked in one (6%). Only five patients received a correct clinical diagnosis before WES. The analyses of patients with a negative genetic diagnosis revealed a phenotype and gene mutation load similar to those of the positive-finding patients but with a lower percentage of ID/DD. CONCLUSIONS: The careful selection of patients by experienced geneticists and the exclusion of chromosomal aberrations raises the positive rate of the molecular diagnosis for CAs to 40%. However, more than half of the patients with CAs still do not have a genetic diagnosis by current technologies.

DYNC1H1 variant associated with epilepsy: Expanding the phenotypic spectrum.

DYNC1H1 variants are associated with peripheral neuronal dysfunction and brain morphology abnormalities resulting in neurodevelopmental delay. However, few studies have focused on the association between DYNC1H1 variants and epilepsy. Herein, we report a case of drug-resistant focal epilepsy associated with a pathogenic variant of DYNC1H1. We further summarized the clinical, genetic, and neuroimaging characteristics of patients with DYNC1H1 variant-associated epilepsy from the relevant literature. This report expands the phenotypic spectrum of DYNC1H1-related disorder to include early-onset epilepsy, which is frequently associated with neurodevelopmental delay and intellectual disability, malformations of cortical development, and neuromuscular, ophthalmic, and orthopedic involvement.

Comparison of GATK and DeepVariant by trio sequencing.

While next-generation sequencing (NGS) has transformed genetic testing, it generates large quantities of noisy data that require a significant amount of bioinformatics to generate useful interpretation. The accuracy of variant calling is therefore critical. Although GATK HaplotypeCaller is a widely used tool for this purpose, newer methods such as DeepVariant have shown higher accuracy in assessments of gold-standard samples for whole-genome sequencing (WGS) and whole-exome sequencing (WES), but a side-by-side comparison on clinical samples has not been performed. Trio WES was used to compare GATK (4.1.2.0) HaplotypeCaller and DeepVariant (v0.8.0). The performance of the two pipelines was evaluated according to the Mendelian error rate, transition-to-transversion (Ti/Tv) ratio, concordance rate, and pathological variant detection rate. Data from 80 trios were analyzed. The Mendelian error rate of the 77 biological trios calculated from the data by DeepVariant (3.09 ± 0.83%) was lower than that calculated from the data by GATK (5.25 ± 0.91%) (p < 0.001). DeepVariant also yielded a higher Ti/Tv ratio (2.38 ± 0.02) than GATK (2.04 ± 0.07) (p < 0.001), suggesting that DeepVariant proportionally called more true positives. The concordance rate between the 2 pipelines was 88.73%. Sixty-three disease-causing variants were detected in the 80 trios. Among them, DeepVariant detected 62 variants, and GATK detected 61 variants. The one variant called by DeepVariant but not GATK HaplotypeCaller might have been missed by GATK HaplotypeCaller due to low coverage. OTC exon 2 (139 bp) deletion was not detected by either method. Mendelian error rate calculation is an effective way to evaluate variant callers. By this method, DeepVariant outperformed GATK, while the two pipelines performed equally in other parameters.

Frequency and spectrum of actionable pathogenic secondary findings in Taiwanese exomes.

BACKGROUND: Exome sequencing has recently become more readily available, and more information about incidental findings has been disclosed. However, data from East Asia are scarce. We studied the application of exome sequencing to the identification of pathogenic/likely pathogenic variants in the ACMG 59 gene list and the frequency of these variants in the Taiwanese population. METHODS: This study screened 161 Taiwanese exomes for variants from the ACMG 59 gene list. The identified variants were reviewed based on information from different databases and the available literature and classified according to the ACMG standard guidelines. RESULTS: We identified seven pathogenic/likely pathogenic variants in eight individuals, with five participants with autosomal recessive variants in one allele and three participants with autosomal dominant variants. Approximately 1.86% (3/161) of the Taiwanese individuals had a reportable pathogenic/likely pathogenic variant as determined by whole-exome sequencing (WES), which was comparable to the proportions published previously in other countries. We further investigated the high carrier rate of rare variants in the ATP7B gene, which might indicate a founder effect in our population. CONCLUSION: This study was the first to provide Taiwanese population data of incidental findings and emphasized a high carrier rate of candidate pathogenic/likely pathogenic variants in the ATP7B gene.