Exome-wide benchmark of difficult-to-sequence regions using short-read next-generation DNA sequencing.

Next-generation DNA sequencing (NGS) in short-read mode has recently been used for genetic testing in various clinical settings. NGS data accuracy is crucial in clinical settings, and several reports regarding quality control of NGS data, primarily focusing on establishing NGS sequence read accuracy, have been published thus far. Variant calling is another critical source of NGS errors that remains unexplored at the single-nucleotide level despite its established significance. In this study, we used a machine-learning-based method to establish an exome-wide benchmark of difficult-to-sequence regions at the nucleotide-residue resolution using 10 genome sequence features based on real-world NGS data accumulated in The Genome Aggregation Database (gnomAD) of the human reference genome sequence (GRCh38/hg38). The newly acquired metric, designated the 'UNMET score,' along with additional lines of structural information from the human genome, allowed us to assess the sequencing challenges within the exonic region of interest using conventional short-read NGS. Thus, the UNMET score could provide a basis for addressing potential sequential errors in protein-coding exons of the human reference genome sequence GRCh38/hg38 in clinical sequencing.

A novel homozygous variant of the PIGK gene caused by paternal disomy in a patient with neurodevelopmental disorder, cerebellar atrophy, and seizures.

Glycosylphosphatidylinositol (GPI)-anchored proteins are located at the cell surface by a covalent attachment between protein and GPI embedded in the plasma membrane. This attachment is catalyzed by GPI transamidase comprising five subunits (PIGK, PIGS, PIGT, PIGU, and GPAA1) in the endoplasmic reticulum. Loss of either subunit of GPI transamidase eliminates cell surface localization of GPI-anchored proteins. In humans, pathogenic variants in either subunit of GPI transamidase cause neurodevelopmental disorders. However, how the loss of GPI-anchored proteins triggers neurodevelopmental defects remains largely unclear. Here, we identified a novel homozygous variant of PIGK, NM_005482:c.481A > G,p. (Met161Val), in a Japanese female patient with neurodevelopmental delay, hypotonia, cerebellar atrophy, febrile seizures, hearing loss, growth impairment, dysmorphic facial features, and brachydactyly. The missense variant was found heterozygous in her father, but not in her mother. Zygosity analysis revealed that the homozygous PIGK variant in the patient was caused by paternal isodisomy. Rescue experiments using PIGK-deficient CHO cells revealed that the p.Met161Val variant of PIGK reduced GPI transamidase activity. Rescue experiments using pigk mutant zebrafish confirmed that the p.Met161Val variant compromised PIGK function in tactile-evoked motor response. We also demonstrated that axonal localization of voltage-gated sodium channels and concomitant generation of action potentials were impaired in pigk-deficient neurons in zebrafish, suggesting a link between GPI-anchored proteins and neuronal defects. Taken together, the missense p.Met161Val variant of PIGK is a novel pathogenic variant that causes the neurodevelopmental disorder.

Case Report: An Adult Case of Poretti-Boltshauser Syndrome Diagnosed by Medical Checkup.

This report describes an adult case of Poretti-Boltshauser syndrome (PTBHS) and with novel variants of LAMA1. A 65-year-old Japanese woman with cerebellar malformation identified during a medical checkup was referred to our hospital. Subsequently, neurological examination, brain imaging, and genetic investigation via whole-exome sequencing were performed. The patient presented with mild cerebellar ataxia and intellectual disability. Magnetic resonance imaging revealed cerebellar dysplasia and cysts and an absence of molar tooth sign. Genetic analysis revealed a novel homozygous variant of c.1711_1712del in LAMA1 (NM_005559.4). Most cases with PTBHS are reported in pediatric patients; however, our patient expressed a mild phenotype and was undiagnosed until her 60 s. These findings suggest that PTBHS should be considered in not only pediatric cerebellar dysplasia but also adult cerebellar ataxia with mild presentation.

Clinical Features of a Japanese Girl With Radio-Tartaglia Syndrome due to a SPEN Truncating Variant.

Radio-Tartaglia syndrome (RATARS) (MIM#619312) is a genetic disorder caused by heterozygous truncating variants of SPEN on chromosome 1p36. This syndrome is extremely rare, with only 34 cases reported to date. RATARS is characterized by developmental delay, hypotonia, and intellectual disability. In this study, we report a Japanese girl with psychomotor delay, hypotonia, and facial features resembling Down syndrome (DS). We identified a de novo heterozygous pathogenic variant of SPEN and diagnosed her with RATARS. The patient was born at 38 weeks and 1 day of gestational age, weighing 2598 g, without respiratory or feeding difficulties. We first considered DS as a differential diagnosis based on the developmental delay with hypotonia and facial features, including an upslanted palpebral fissure, hypertelorism, epicanthus folds, and a low nose; however, it was ruled out after cytogenetic testing. Microarray analysis revealed no pathogenic aberrations. We performed trio-based whole exome sequencing and identified a recurrent pathogenic variant of SPEN:NM_015001.3:c.6223_6227del, p.(Ser2075GlufsTer46). Although some features of RATARS have been reported to be similar to those of 1p36 deletion syndrome, facial similarity to DS was a characteristic of our case. Whether this feature is unique to the patient or relatively common in individuals with RATARS should be discussed further as more cases of individuals with RATARS are reported.

Biallelic loss-of-function variants of EZH1 cause a novel developmental disorder with central precocious puberty.

Pathogenic variants of polycomb repressive complex-2 (PRC2) subunits are associated with overgrowth syndromes and neurological diseases. EZH2 is a major component of PRC2 and mediates the methylation of H3K27 trimethylation (H3K27me3). Germline variants of EZH2 have been identified as a cause of Weaver syndrome (WS), an overgrowth/intellectual disability (OGID) syndrome characterized by overgrowth, macrocephaly, accelerated bone age, intellectual disability (ID), and characteristic facial features. Germline variants of SUZ12 and EED, other components of PRC2, have also been reported in the WS or Weaver-like syndrome. EZH1 is a homolog of EZH2 that interchangeably associates with SUZ12 and EED. Recently, pathogenic variants of EZH1 have been reported in individuals with dominant and recessive neurodevelopmental disorders. We herein present sisters with biallelic loss-of-function variants of EZH1. They showed developmental delay, ID, and central precocious puberty, but not the features of WS or other OGID syndromes.

Renal coloboma syndrome/dominant optic atrophy with severe retinal atrophy and de novo digenic mutations in PAX2 and OPA1.

Renal coloboma syndrome (RCS) and dominant optic atrophy are mainly caused by heterozygous mutations in PAX2 and OPA1, respectively. We describe a patient with digenic mutations in PAX2 and OPA1. A female infant was born without perinatal abnormalities. Magnetic resonance imaging at 4 months of age showed bilateral microphthalmia and optic nerve hypoplasia. Appropriate body size was present at 2 years of age, and mental development was favorable. Color fundus photography revealed severe retinal atrophy in both eyes. Electroretinography showed slight responses in the right eye, but no responses in the left eye, suggesting a high risk of blindness. Urinalysis results were normal, creatinine-based estimated glomerular filtration rate was 63.5 mL/min/1.73 m2, and ultrasonography showed bilateral hypoplastic kidneys. Whole exome sequencing revealed de novo frameshift mutations in PAX2 and OPA1. Both variants were classified as pathogenic (PVS1, PS2, PM2) based on the guidelines from the American College of Medical Genetics and Genomics (ACMG). Genetic testing for ocular diseases should be considered for patients with suspected RCS and a high risk of total blindness.

STAT6 gain-of-function variant exacerbates multiple allergic symptoms.

BACKGROUND: Allergic diseases were long considered to be complex multifactorial disorders. However, recent findings indicate that severe allergic inflammation can be caused by monogenic immune defects. OBJECTIVES: We sought to clarify the molecular pathogenesis of a patient with early-onset multiple allergic diseases, a high serum IgE level, hypereosinophilia, treatment-resistant severe atopic dermatitis with increased dermal collagen fiber deposition, and eosinophilic gastrointestinal disorder with numerous polypoid nodules. METHODS: A missense variant in STAT6 was identified, and its function was examined using peripheral blood, transfected HEK293 cells, lymphoblastoid cell lines, and knock-in mice with the corresponding mutation. RESULTS: Whole-exome sequencing identified a de novo heterozygous missense variant in signal transducer and activator of transcription 6 (STAT6) (p.Asp419Asn). Luciferase reporter assay revealed that the transcriptional activity of this STAT6 mutant was upregulated even without IL-4 stimulation. Phosphorylation of STAT6 was not observed in either the patient's TH2 cells or lymphoblastoid cell lines without stimulation, whereas it was induced more strongly in both by IL-4 stimulation compared with healthy controls. STAT6 protein was present in the nuclear fraction of the lymphoblastoid cell lines of the patient even in the absence of IL-4 stimulation. The patient's gastric mucosa showed upregulation of STAT6-, fibrosis-, and germinal center formation-related molecules. Some of the knock-in mice with the corresponding mutation spontaneously developed dermatitis with skin thickening and eosinophil infiltration. Moreover, serum IgE levels and mRNA expression of type 2 cytokines were increased in the knock-in mice-with or without development of spontaneous dermatitis-compared with the wild-type mice. CONCLUSIONS: A novel STAT6 gain-of-function variant is a potential cause of primary atopic disorders.

Biallelic CC2D2A variants, SNV and LINE-1 insertion simultaneously identified in siblings using long-read whole-genome sequencing and haplotype phasing.

Joubert syndrome (JBTS) is characterized by a magnetic resonance imaging appearance called 'molar tooth sign', neonatal breathing dysregulation and hypotonia, and developmental delay. Whole-exome analysis based on short-read sequencing has often contributed to the identification of causative single-nucleotide variants in patients clinically diagnosed with JBTS. However, ~10% of them are still undiagnosed even though a single possible pathogenic variant has been identified. We report a successful identification of biallelic variants using long-read whole-genome sequencing and haplotype phasing analysis in a family with two Japanese siblings having morphological brain abnormalities. The affected siblings had a novel nonsynonymous variant (CC2D2A:NM_001080522.2:c.4454A>G:p.(Tyr1485Cys)) and an exonic insertion of Long INterspercsed Element-1 (LINE-1). The allelicity of these variants was clearly proven without the data of parents. Finally, our survey of in-house genome sequencing data indicates that there are rare carriers of CC2D2A related diseases, who harbour the exonic LINE-1 insertion in the CC2D2A gene.

The novel and recurrent variants in exon 31 of CREBBP in Japanese patients with Menke-Hennekam syndrome.

Menke-Hennekam syndrome-1 (MKHK1) is a congenital disorder caused by the heterozygous variants in exon 30 or 31 of CREBBP (CREB binding protein) gene mapped on 16p13.3. It is characterized by psychomotor delay, variable impairment of intellectual disability (ID), feeding difficulty, autistic behavior, hearing impairment, short stature, microcephaly, and facial dysmorphisms. The CREBBP loss-of-function variants cause Rubinstein-Taybi syndrome-1 (RSTS1). The function of CREBBP leading to MKHK1 has not been clarified so far, and the phenotype of MKHK1 significantly differs from that of RSTS1. We examined six patients with de novo pathogenic variants affecting the last exon of CREBBP, and they shared the clinical features of MKHK1. This study revealed that one frameshift and three nonsense variants of CREBBP cause MKHK1, and inferred that the nonsense variants of the last exon could further help in the elucidation of the etiology of MKHK1.

Four pedigrees with aminoacyl-tRNA synthetase abnormalities.

Aminoacyl tRNA synthetases (ARSs) are highly conserved enzymes that link amino acids to their cognate tRNAs. Thirty-seven ARSs are known and their deficiencies cause various genetic disorders. Variants in some ARSs are associated with the autosomal dominant inherited form of axonal neuropathy, including Charcot-Marie-Tooth (CMT) disease. Variants of genes encoding ARSs often cause disorders in an autosomal recessive fashion. The clinical features of cytosolic ARS deficiencies are more variable, including systemic features. Deficiencies of ARSs localized in the mitochondria are often associated with neurological disorders including Leigh and early-onset epileptic syndromes. Whole exome sequencing (WES) is an efficient way to identify the genes causing various symptoms in patients. We identified 4 pedigrees with novel compound heterozygous variants in ARS genes (WARS1, MARS1, AARS2, and PARS2) by WES. Some unique manifestations were noted. The number of patients with ARSs has been increasing since the application of WES. Our findings broaden the known genetic and clinical spectrum associated with ARS variants.

A novel missense variant of the GNAI3 gene and recognisable morphological characteristics of the mandibula in ARCND1.

Auriculocondylar syndrome (ARCND) is an autosomal monogenic disorder characterised by external ear abnormalities and micrognathia due to hypoplasia of the mandibular rami, condyle and coronoid process. Genetically, three subtypes of ARCND (ARCND1, ARCND2 and ARCND3) have been reported. To date, five pathogenic variants of GNAI3 have been reported in ARCND1 patients. Here, we report a novel variant of GNAI3 (NM_006496:c.807C>A:p.(Asn269Lys)) in a Japanese girl with micrognathia using trio-based whole exome sequencing analysis. The GNAI3 gene encodes a heterotrimeric guanine nucleotide-binding protein. The novel variant locates the guanine nucleotide-binding site, and the substitution was predicted to interfere with guanine nucleotide-binding by in silico structural analysis. Three-dimensional computer tomography scan, or cephalogram, displayed severely hypoplastic mandibular rami and fusion to the medial and lateral pterygoid plates, which have been recognised in other ARCND1 patients, but have not been described in ARCND2 and ARCND3, suggesting that these may be distinguishable features in ARCND1.

Genetic and phenotypic analysis of 101 patients with developmental delay or intellectual disability using whole-exome sequencing.

Whole-exome sequencing (WES) enables identification of pathogenic variants, including copy number variants (CNVs). In this study, we performed WES in 101 Japanese patients with unexplained developmental delay (DD) or intellectual disability (ID) (63 males and 38 females), 98 of them with trio-WES. Pathogenic variants were identified in 54 cases (53.5%), including four cases with pathogenic CNVs. In one case, a pathogenic variant was identified by reanalysis of exome data; and in two cases, two molecular diagnoses were identified. Among 58 pathogenic variants, 49 variants occurred de novo in 48 patients, including two somatic variants. The accompanying autism spectrum disorder and external ear anomalies were associated with detection of pathogenic variants with odds ratios of 11.88 (95% confidence interval [CI] 2.52-56.00) and 3.46 (95% CI 1.23-9.73), respectively. These findings revealed the importance of reanalysis of WES data and detection of CNVs and somatic variants in increasing the diagnostic yield for unexplained DD/ID. In addition, genetic testing is recommended when patients suffer from the autism spectrum disorder or external ear anomalies, which potentially suggests the involvement of genetic factors associated with gene expression regulation.

Blended phenotype of combination of HERC2 and AP3B2 deficiency and Angelman syndrome caused by paternal isodisomy of chromosome 15.

Angelman syndrome is a neurodevelopmental disorder characterized by intellectual disability (ID), a distinctive gait pattern, abnormal behaviors, severe impairment in language development, and characteristic facial features. Most cases are caused by the absence of a maternal contribution to the imprinted region on chromosome 15q11-q13. Here, we present the first reported case of a 3-year-old boy with an atypical phenotype of Angelman syndrome due to uniparental isodisomy with two recessive homozygous pathogenic variants: in HERC2 and AP3B2. Known phenotypes related to HERC2 and AP3B2 include ID and early infantile epileptic encephalopathy, respectively. The patient had severe global developmental delay and profound ID and showed a happy demeanor, stereotypic laughter, and hand-flapping movements, but also irritability. Craniofacial dysmorphic features, including brachycephaly, strabismus, wide ala nasi, short philtrum, wide open mouth, and slight hypopigmentation were seen. Progressive microcephaly was noted. Magnetic resonance imaging of the brain showed delayed myelination and cerebral atrophy. Trio whole exome sequencing and CGH-SNP array analysis revealed paternal uniparental isodisomy of chromosome 15 and two coexisting recessive diseases resulting from homozygous HERC2 and AP3B2 pathogenic variants. The pathogenic variant in HERC2 was inherited from his heterozygous-carrier father, and the variant in AP3B2 was de novo. We suppose that these unusual features were the combination of the effect of three concomitant disorders.

Clinical spectrum of individuals with de novo EBF3 variants or deletions.

Hypotonia, ataxia and delayed development syndrome (HADDS) (MIM#617330) is a neurodevelopmental disorder caused by heterozygous pathogenic variants in EBF3 (MIM; 607,407), which is located on chromosome 10q26, and was first reported in 2017. To date, missense, nonsense and frameshift variants have been reported as causes of HADDS, and EBF3 pathogenic variants have been predicted to result in nonsense-mediated mRNA decay and haploinsufficiency. It was also reported that total deletion of EBF3 associated with a 10q26.3 microdeletion also causes HADDS symptoms, supporting the concept that HADDS results from haploinsufficiency of EBF3. Here, we report eight unrelated individuals with heterozygous pathogenic variants of EBF3 or haploinsufficiency of EBF3 due to 10q26 deletion, who exhibit clinical findings including craniofacial features of HADDS. In a detailed examination of clinical manifestations in this study, revealed that neurogenic bladder was diagnosed in infancy (the median 6.5 months), was more frequent than previously reported, and required cystostomy in all but one case. For psychomotor delay, it was also found that their motor/skills values were significantly lower than their cognition/adaptation values (p = 0.0016; paired t-test). Therefore, that HADDS is a recognizable syndrome that shares its characteristic facial features, and that neurogenic bladder diagnosed in infancy and psychomotor delay with marked delay in motor/skills are noteworthy findings in the diagnosis and management of individuals with HADDS.

HECW2-related disorder in four Japanese patients.

The HECT, C2, and WW domain containing E3 ubiquitin protein ligase 2 gene (HECW2) is involved in protein ubiquitination. Several genes associated with protein ubiquitination have been linked to neurodevelopmental disorders. HECW2-related disorder has been established through the identification of de novo variants in HECW2 in patients with neurodevelopmental disorders with hypotonia, seizures, and absent language. Recently, we identified novel HECW2 variants in four Japanese patients with neurodevelopmental disorders. Regarding motor development, two of the patients cannot walk, whereas the other two can walk with an unsteady gait, owing to hypotonia. All HECW2 variants, including those that were previously reported, are missense, and no loss-of-function variants have been identified. Most of the identified variants are located around the HECT domain. These findings suggest that the dominant negative effects of missense variants around the HECT domain may be the mechanism underlying HECW2-related disorder.

Successful kidney transplantation in a patient with neonatal-onset ILNEB.

BACKGROUND: ILNEB constitute an autosomal recessive disorder caused by homozygous or compound heterozygous mutation of the gene for the ITGA3. To date, 8 ILNEB patients have been reported, but all 6 neonatal-onset ILNEB patients suffered early death within 2 years. The most common cause of death among previously reported ILNEB patients was exacerbation of the respiratory condition. METHODS: In this study, we describe a case of ILNEB with neonatal onset in a female patient and the genetic and histopathological testing performed. RESULTS: Our patient had a compound heterozygous mutation in ITGA3. Compared to previously reported patients, this patient exhibited milder clinical and histopathological characteristics. After experiencing a life-threatening respiratory infection at 8 months old, the patient started periodic subcutaneous immunoglobulin treatment once every 1-2 weeks for nephrotic-range proteinuria-induced secondary hypogammaglobulinemia. At the age of 3 years, proteinuria gradually increased with severe edema despite strict internal management. Therefore, our patient underwent unilateral nephrectomy and insertion of a peritoneal dialysis catheter followed by another unilateral nephrectomy. One month later, she underwent an ABO-compatible living-donor kidney transplantation at the age of 4 years. CONCLUSIONS: Our patient is a neonatal-onset ILNEB patient who survived for more than 2 years and underwent successful kidney transplantation.

Recurrent de novo MAPK8IP3 variants cause neurological phenotypes.

c-Jun-amino-terminal kinase-interacting protein 3 (JIP3), encoded by MAPK8IP3, is an adaptor protein of the kinesin-1 complex and essential for axonal transport in neurons. However, an association between MAPK8IP3 variants and human disease has not been established. We identified 5 individuals from four families with recurrent de novo variants c.1732C>T (p.Arg578Cys) and c.3436C>T (p.Arg1146Cys) in MAPK8IP3. The core phenotype includes spastic diplegia, intellectual disability, cerebral atrophy, and corpus callosum hypoplasia. Zebrafish embryos overexpressing human mutant JIP3 showed axon varicosities of the posterior lateral line nerve, suggesting an adverse effect on the developing axons. Our results suggest that MAPK8IP3 variants cause a neurodevelopmental disease. ANN NEUROL 2019;85:927-933.

Parental somatogonadal COL2A1 mosaicism contributes to intrafamilial recurrence in a family with type 2 collagenopathy.

The COL2A1 gene encodes the alpha-1 chain of procollagen type 2. Pathogenic variants in the COL2A1 gene are associated with several different types of skeletal dysplasia collectively known as type 2 collagenopathies. Type 2 collagenopathies have an autosomal dominant inheritance. Some germline or somatogonadal mosaicism cases have been reported. We investigated whether somatogonadal mosaicism occurred in a family with two children suspected of type 2 collagenopathies or related diseases. First, we detected a pathogenic variant in the COL2A1 gene in the two affected children by whole exome sequencing (WES). Next, we performed targeted deep sequencing to their parents without the variant by WES. A low level of COL2A1 mosaicism was revealed in the mother's tissues. We concluded that the mother had somatogonadal mosaicism with the COL2A1 mutation arose in the epiblast, and that the intrafamilial recurrence rate of the disease by the somatogonadal mosaicism was higher than by the germline mosaicism. This report suggests that parental low-level mosaicism should be evaluated in those parents with children carrying de novo germline mutations and the targeted deep sequencing is useful to detect them.

NT5E Genetic Mutation Is a Rare But Important Cause of Intermittent Claudication and Chronic Limb-Threatening Ischemia.

BACKGROUND: NT5Egenetic mutations are known to result in calcification of joints and arteries (CALJA), and worldwide, 14 patients from 7 families have been reported.Methods and Results:A total of 5 patients from 2 independent families with CALJA were found in Japan. Of them, 3 complained of intermittent claudication (IC), and 1 suffered from bilateral chronic limb-threatening ischemia (CLTI). Whole-exome sequencing analysis revealed an identical mutation pattern (c.G3C on the exon 1 start codon) that was unique compared withNT5Emutations reported in other countries. CONCLUSIONS: Vascular specialists need to recognize CALJA as a rare cause of ischemic IC and CLTI.

Entire FGF12 duplication by complex chromosomal rearrangements associated with West syndrome.

Complex rearrangements of chromosomes 3 and 9 were found in a patient presenting with severe epilepsy, developmental delay, dysmorphic facial features, and skeletal abnormalities. Molecular cytogenetic analysis revealed 46,XX.ish der(9)(3qter→3q28::9p21.1→9p22.3::9p22.3→9qter)(RP11-368G14+,RP11-299O8-,RP11-905L2++,RP11-775E6++). Her dysmorphic features are consistent with 3q29 microduplication syndrome and inv dup del(9p). Trio-based WES of the patient revealed no pathogenic single nucleotide variants causing epilepsy, but confirmed a 3q28q29 duplication involving FGF12, which encodes fibroblast growth factor 12. FGF12 positively regulates the activity of voltage-gated sodium channels. Recently, only one recurrent gain-of-function variant [NM_021032.4:c.341G>A:p.(Arg114His)] in FGF12 was found in a total of 10 patients with severe early-onset epilepsy. We propose that the patient's entire FGF12 duplication may be analogous to the gain-of-function variant in FGF12 in the epileptic phenotype of this patient.