Japanese Public Health Insurance System's new genomic strategic action to shorten the "diagnostic odyssey" for patients with rare and intractable diseases.

In June 2024, the Japanese government introduced a new genomic strategic action to shorten the "diagnostic odyssey" for patients with rare and intractable diseases: Six groups of rare diseases, (i) Muscle weakness group, (ii) Growth retardation, intellectual disability, and characteristic facial features group, (iii) Intellectual disability/epilepsy group, (iv) Cardiomyopathy group (mainly adult onset) (v) Proteinuria group, (vi) Fever, inflammation, skin rash, osteoarthritis group, have been newly recognized as "difficult-to-differentiate disorders" and comprehensive genomic testing can be reimbursed when patients belong to one of the six groups and certain requirements are met. The introduction of comprehensive genomic testing will improve the diagnosis rate of diseases and have significant potential to enhance Japan's rare and intractable disease policy. The new strategy in Japan and its rationale will be a reference for insurance reimbursement of comprehensive genomic testing in other countries that have universal health coverage supported by the public health insurance system.

Biallelic structural variants in three patients with ERCC8-related Cockayne syndrome and a potential pitfall of copy number variation analysis.

Cockayne syndrome (CS) is a rare autosomal recessive disorder caused by mutations in ERCC8 or ERCC6. Most pathogenic variants in ERCC8 are single nucleotide substitutions. Structural variants (SVs) have been reported in patients with ERCC8-related CS. However, comprehensive molecular detection, including SVs of ERCC8, in CS patients remains problematic. Herein, we present three Japanese patients with ERCC8-related CS in whom causative SVs were identified using whole-exome-based copy number variation (CNV) detection tools. One patient showed compound heterozygosity for a 259-kb deletion and a deletion of exon 4 which has previously been reported as an Asia-specific variant. The other two patients were homozygous for the same exon 4 deletion. The exon 4 deletion was detected only by the ExomeDepth software. Intrigued by the discrepancy in the detection capability of various tools for the SVs, we evaluated the analytic performance of four whole-exome-based CNV detection tools using an exome data set from 337 healthy individuals. A total of 1,278,141 exons were predicted as being affected by the 4 CNV tools. Interestingly 95.1% of these affected exons were detected by one tool alone. Thus, we expect that the use of multiple tools may improve the detection rate of SVs from aligned exome data.

Digital clubbing without hypoxia for lysinuric protein intolerance.

Digital clubbing is characterized by bulbous enlargement of the terminal segments of the fingers. Hypotheses including hypoxia have been proposed for the pathogenesis of digital clubbing, but the exact pathogenesis of digital clubbing is still uncertain. Lysinuric protein intolerance (LPI) is caused by pathogenic variants in SLC7A7 and is often associated with interstitial lung disease. Previously two patients of LPI with digital clubbing but without hypoxia have been reported. It is unclear whether digital clubbing in LPI is secondary to hypoxia or directly related to SLC7A7 deficiency. Here we report a 6-year-old Japanese boy presented with digital clubbing without hypoxia. He had episodic vomiting, each episode consisting of a single vomiting event occurring once a month, and his growth had been delayed. He had interstitial lung disease and hepatomegaly. He had compound heterozygous pathogenic variants in the SLC7A7, leading to the diagnosis of LPI. Together with the two previously reported patients mentioned above, we conclude that digital clubbing can occur in the absence of hypoxia. Digital clubbing in the absence of hypoxia has been observed in two genetic disorders related to prostaglandin (PG) E2, HPGD and SLCO2A1. PGE2 synthesis is primarily regulated by the cyclooxygenase 2, which plays a critical role in the control of inflammation. A high urine PGE level in the patient was compatible with the notion that PGE2 production may be increased in LPI. The occurrence of digital clubbing in the absence of hypoxia in LPI patients with SLC7A7 may be attributed to the mechanism of increased PGE2 production.

Biallelic null variants in PNPLA8 cause microcephaly by reducing the number of basal radial glia.

Patatin-like phospholipase domain-containing lipase 8 (PNPLA8), one of the calcium-independent phospholipase A2 enzymes, is involved in various physiological processes through the maintenance of membrane phospholipids. Biallelic variants in PNPLA8 have been associated with a range of paediatric neurodegenerative disorders. However, the phenotypic spectrum, genotype-phenotype correlations and the underlying mechanisms are poorly understood. Here, we newly identified 14 individuals from 12 unrelated families with biallelic ultra-rare variants in PNPLA8 presenting with a wide phenotypic spectrum of clinical features. Analysis of the clinical features of current and previously reported individuals (25 affected individuals across 20 families) showed that PNPLA8-related neurological diseases manifest as a continuum ranging from variable developmental and/or degenerative epileptic-dyskinetic encephalopathy to childhood-onset neurodegeneration. We found that complete loss of PNPLA8 was associated with the more profound end of the spectrum, with congenital microcephaly. Using cerebral organoids generated from human induced pluripotent stem cells, we found that loss of PNPLA8 led to developmental defects by reducing the number of basal radial glial cells and upper-layer neurons. Spatial transcriptomics revealed that loss of PNPLA8 altered the fate specification of apical radial glial cells, as reflected by the enrichment of gene sets related to the cell cycle, basal radial glial cells and neural differentiation. Neural progenitor cells lacking PNPLA8 showed a reduced amount of lysophosphatidic acid, lysophosphatidylethanolamine and phosphatidic acid. The reduced number of basal radial glial cells in patient-derived cerebral organoids was rescued, in part, by the addition of lysophosphatidic acid. Our data suggest that PNPLA8 is crucial to meet phospholipid synthetic needs and to produce abundant basal radial glial cells in human brain development.

Biallelic loss-of-function variants in the centriolar protein CCP110 leads to a ciliopathy-like phenotype.

CCP110 (centriolar coiled coil protein 110, also known as CP110) is one of the essential proteins localized in the centrosome that plays critical roles in the regulation of the cell cycle and also in the initiation of ciliogenesis. So far, no human congenital disorders have been identified to be associated with pathogenic variants of CCP110. Mice with biallelic loss-of-function variants of Ccp110 (Ccp110-/-) are known to manifest multiple organ defects, including a small body size, polydactyly, omphalocele, congenital heart defects, cleft palate, short ribs, and a small thoracic cage, a pattern of abnormalities closely resembling that in "ciliopathies" in humans. Herein, we report a 7-month-old male infant who presented with growth failure and skeletal abnormalities, including a narrow thorax and severe brachydactyly. Trio exome analysis of the genomic DNA of the patient and his parents showed that the patient was a compound heterozygote for truncating variants of CCP110, including a frameshift variant NM_001323572.2:c.856_857del, p.(Val286Leufs*5) inherited from the father, and a nonsense variant NM_001323572.2:c.1129C>T, p.(Arg377*) inherited from the mother. The strikingly similar pattern of malformations between Ccp110-/- mice and the 7-month-old male infant reported herein carrying unequivocal truncating CCP110 variants strongly supports the contention that CCP110 is a novel disease-causative gene.

Truncating variants of the sterol recognition region of SHH cause hypertelorism phenotype rather than hypotelorism-holoprosencephaly.

Sonic hedgehog signaling molecule (SHH) is a key molecule in the cilia-mediated signaling pathway and a critical morphogen in embryogenesis. The association between loss-of-function variants of SHH and holoprosencephaly is well established. In mice experiments, reduced or increased signaling of SHH have been shown to be associated with narrowing or excessive expansion of the facial midline, respectively. Herein, we report two unrelated patients with de novo truncating variants of SHH presenting with hypertelorism rather than hypotelorism. The first patient was a 13-year-old girl. Her facial features included hypertelorism, strabismus, telecanthus, malocclusion, frontal bossing, and wide widow's peak. She had borderline developmental delay and agenesis of the corpus callosum. She had a nonsense variant of SHH: Chr7(GRCh38):g.155802987C > T, NM_000193.4:c.1302G > A, p.(Trp434*). The second patient was a 25-year-old girl. Her facial features included hypertelorism and wide widow's peak. She had developmental delay and agenesis of the corpus callosum. She had a frameshift variant of SHH: Chr7(GRCh38):g.155803072_155803074delCGGinsT, NM_000193.4:c.1215_1217delCCGinsA, p.(Asp405Glufs*92). The hypertelorism phenotype contrasts sharply with the prototypical hypotelorism-holoprosencephaly phenotype associated with loss-of-function of SHH. We concluded that a subset of truncating variants of SHH could be associated with hypertelorism rather than hypotelorism.

Successful skipping of abnormal pseudoexon by antisense oligonucleotides in vitro for a patient with beta-propeller protein-associated neurodegeneration.

Pathogenic variants in WDR45 on chromosome Xp11 cause neurodegenerative disorder beta-propeller protein-associated neurodegeneration (BPAN). Currently, there is no effective therapy for BPAN. Here we report a 17-year-old female patient with BPAN and show that antisense oligonucleotide (ASO) was effective in vitro. The patient had developmental delay and later showed extrapyramidal signs since the age of 15 years. MRI findings showed iron deposition in the globus pallidus and substantia nigra on T2 MRI. Whole genome sequencing and RNA sequencing revealed generation of pseudoexon due to inclusion of intronic sequences triggered by an intronic variant that is remote from the exon-intron junction: WDR45 (OMIM #300526) chrX(GRCh37):g.48935143G > C, (NM_007075.4:c.235 + 159C > G). We recapitulated the exonization of intron sequences by a mini-gene assay and further sought antisense oligonucleotide that induce pseudoexon skipping using our recently developed, a dual fluorescent splicing reporter system that encodes two fluorescent proteins, mCherry, a transfection marker designed to facilitate evaluation of exon skipping and split eGFP, a splicing reaction marker. The results showed that the 24-base ASO was the strongest inducer of pseudoexon skipping. Our data presented here have provided supportive evidence for in vivo preclinical studies.

SALL4 deletion and kidney and cardiac defects associated with VACTERL association.

Congenital anomalies of the kidney and urinary tract (CAKUT) can be a part of the VACTERL association, which represents the non-random combination of the following congenital anomalies: vertebral anomalies, anal anomalies, cardiac anomalies, tracheal-esophageal anomalies, kidney anomalies, and limb anomalies. VACTERL association is generally considered to be a non-genetic condition. Exceptions include a patient with a heterozygous nonsense SALL4 variant and anal stenosis, tetralogy of Fallot, sacro-vertebral fusion, and radial and thumb anomalies. SALL4 encodes a transcription factor that plays a critical role in kidney morphogenesis. Here, we report a patient with VACTERL association and a heterozygous 128-kb deletion spanning SALL4 who presented with renal hypoplasia, radial and atrio-septal defects, and patent ductus arteriosus. The present report of SALL4 deletion, in addition to a previously reported patient with VACTERL association phenotype and SALL4 nonsense mutation, further supports the notion that SALL4 haploinsufficiency can lead to VACTERL association.

Time-dependent cell-state selection identifies transiently expressed genes regulating ILC2 activation.

The decision of whether cells are activated or not is controlled through dynamic intracellular molecular networks. However, the low population of cells during the transition state of activation renders the analysis of the transcriptome of this state technically challenging. To address this issue, we have developed the Time-Dependent Cell-State Selection (TDCSS) technique, which employs live-cell imaging of secretion activity to detect an index of the transition state, followed by the simultaneous recovery of indexed cells for subsequent transcriptome analysis. In this study, we used the TDCSS technique to investigate the transition state of group 2 innate lymphoid cells (ILC2s) activation, which is indexed by the onset of interleukin (IL)-13 secretion. The TDCSS approach allowed us to identify time-dependent genes, including transiently induced genes (TIGs). Our findings of IL4 and MIR155HG as TIGs have shown a regulatory function in ILC2s activation.

Neurochemistry evaluated by magnetic resonance spectroscopy in a patient with FBXO28-related developmental and epileptic encephalopathy.

BACKGROUND: Mutations in the FBXO28 gene, which encodes FBXO28, one of the F-box protein family, may cause developmental and epileptic encephalopathy (DEE). FBXO28-related DEE is radiologically characterized by cerebral atrophy, delayed/abnormal myelination, and brain malformation; however, no neurochemical analyses have been reported. CASE REPORT: A female Japanese infant presented with severe psychomotor delay, epileptic spasms, and visual impairment. Whole-exome sequencing revealed a de novo variant of the FBXO28 gene, leading to the diagnosis of FBXO28-related DEE. Magnetic resonance (MR) spectroscopy at 6, 12, and 32 months revealed decreased N-acetylaspartate and choline-containing compounds and increased levels of myoinositol. CONCLUSION: MR spectroscopy revealed neurochemical derangement in FBXO28-related DEE, that is, disturbed myelination secondary to neuronal damage with astrogliosis.

Café-au-lait Spots and Cleft Palate: Not a Chance Association.

The recognition of syndromic forms of cleft palate is important for condition-specific management. Here, we report a patient with cleft palate, congenital heart disease, intellectual disability, and café-au-lait spots who had a deletion of chromosome 15q14. The identification of the precise breakpoints using a Nanopore-based long-read sequencer showed that the deletion spanned MEIS2 and SPRED1 loci. Cleft palate and café-au-lait spots can be ascribed to MEIS2 and SPRED1, respectively. Patients with cleft palate and café-au-lait spots should be encouraged to undergo a detailed genomic evaluation, including screening for a 15q14 deletion, to enable appropriate anticipatory medico-surgical management and genetic counseling.

Heterozygous loss-of-function DHX9 variants are associated with neurodevelopmental disorders: Human genetic and experimental evidences.

DExH-box helicases are involved in unwinding of RNA and DNA. Among the 16 DExH-box genes, monoallelic variants of DHX16, DHX30, DHX34, and DHX37 are known to be associated with neurodevelopmental disorders. In particular, DHX30 is well established as a causative gene for neurodevelopmental disorders. Germline variants of DHX9, the closest homolog of DHX30, have not been reported until now as being associated with congenital disorders in humans, except that one de novo heterozygous variant, p.(Arg1052Gln) of the gene was identified during comprehensive screening in a patient with autism; unfortunately, the phenotypic details of this individual are unknown. Herein, we report a patients with a heterozygous de novo missense variant, p.(Gly414Arg) of DHX9 who presented with a short stature, intellectual disability, and ventricular non-compaction cardiomyopathy. The variant was located in the glycine codon of the ATP-binding site, G-C-G-K-T. To assess the pathogenicity of these variants, we generated transgenic Drosophila lines expressing human wild-type and mutant DHX9 proteins: 1) the mutant proteins showed aberrant localization both in the nucleus and the cytoplasm; 2) ectopic expression of wild-type protein in the visual system led to the rough eye phenotype, whereas expression of the mutant proteins had minimal effect; 3) overexpression of the wild-type protein in the retina led to a reduction in axonal numbers, whereas expression of the mutant proteins had a less pronounced effect. Furthermore, in a gene-editing experiment of Dhx9 G416 to R416, corresponding to p.(Gly414Arg) in humans, heterozygous mice showed a reduced body size, reduced emotionality, and cardiac conduction abnormality. In conclusion, we established that heterozygosity for a loss-of-function variant of DHX9 can lead to a new neurodevelopmental disorder.

Topologically associating domain underlies tissue specific expression of long intergenic non-coding RNAs.

Accumulating evidence indicates that long intergenic non-coding RNAs (lincRNAs) show more tissue-specific expression patterns than protein-coding genes (PCGs). However, although lincRNAs are subject to canonical transcriptional regulation like PCGs, the molecular basis for the specificity of their expression patterns remains unclear. Here, using expression data and coordinates of topologically associating domains (TADs) in human tissues, we show that lincRNA loci are significantly enriched in the more internal region of TADs compared to PCGs and that lincRNAs within TADs have higher tissue specificity than those outside TADs. Based on these, we propose an analytical framework to interpret transcriptional status using lincRNA as an indicator. We applied it to hypertrophic cardiomyopathy data and found disease-specific transcriptional regulation: ectopic expression of keratin at the TAD level and derepression of myocyte differentiation-related genes by E2F1 with down-regulation of LINC00881. Our results provide understanding of the function and regulation of lincRNAs according to genomic structure.

Simple and efficient differentiation of human iPSCs into contractible skeletal muscles for muscular disease modeling.

Pathophysiological analysis and drug discovery targeting human diseases require disease models that suitably recapitulate patient pathology. Disease-specific human induced pluripotent stem cells (hiPSCs) differentiated into affected cell types can potentially recapitulate disease pathology more accurately than existing disease models. Such successful modeling of muscular diseases requires efficient differentiation of hiPSCs into skeletal muscles. hiPSCs transduced with doxycycline-inducible MYOD1 (MYOD1-hiPSCs) have been widely used; however, they require time- and labor-consuming clonal selection, and clonal variations must be overcome. Moreover, their functionality should be carefully examined. Here, we demonstrated that bulk MYOD1-hiPSCs established with puromycin selection rather than G418 selection showed rapid and highly efficient differentiation. Interestingly, bulk MYOD1-hiPSCs exhibited average differentiation properties of clonally established MYOD1-hiPSCs, suggesting that it is possible to minimize clonal variations. Moreover, disease-specific hiPSCs of spinal bulbar muscular atrophy (SBMA) could be efficiently differentiated via this method into skeletal muscle that showed disease phenotypes, suggesting the applicability of this method for disease analysis. Finally, three-dimensional muscle tissues were fabricated from bulk MYOD1-hiPSCs, which exhibited contractile force upon electrical stimulation, indicating their functionality. Thus, our bulk differentiation requires less time and labor than existing methods, efficiently generates contractible skeletal muscles, and may facilitate the generation of muscular disease models.

Precise definition of the breakpoints of an apparently balanced translocation between chromosome 3q26 and chromosome 7q36: Role of KMT2C disruption.

When a de novo balanced reciprocal translocation is identified in the patient, the cause of phenotype of the patient can be explained by detecting the breakpoints of the genes. Here, we report a 3-year-old patient with developmental delay, autism spectrum disorder, and distinctive facial features who had an apparently balanced translocation between chromosome 3q26 and chromosome 7q36. Nanopore long-read sequencing revealed that balanced translocation disrupted the KMT2C gene, the haploinsufficiency of which leads to Kleefstra syndrome 2 characterized by delayed psychomotor development, variable intellectual disability and mild dysmorphism. Nanopore long-read sequencing was shown to be useful in elucidating the exact genetic etiology of patients with nonspecific clinical findings.

Diagnosis of Prader-Willi syndrome and Angelman syndrome by targeted nanopore long-read sequencing.

The CpG island flanking the promoter region of SNRPN on chromosome 15q11.2 contains CpG sites that are completely methylated in the maternally derived allele and unmethylated in the paternally derived allele. Both unmethylated and methylated alleles are observed in normal individuals. Only the methylated allele is observed in patients with Prader-Willi syndrome, whereas only the unmethylated allele is observed in those with Angelman syndrome. Hence, detection of aberrant methylation at the differentially methylated region is fundamental to the molecular diagnosis of Prader-Willi syndrome and Angelman syndromes. Traditionally, bisulfite treatment and methylation-sensitive restriction enzyme treatment or methylation-specific multiplex ligation-dependent probe amplification (MS-MLPA) have been used. We here developed a long-read sequencing assay that can distinguish methylated and unmethylated CpG sites at 15q11.2 by the difference in current intensity generated from nanopore reads. We successfully diagnosed 4 Prader-Willi syndrome patients and 3 Angelman syndrome patients by targeting differentially methylated regions. Concurrent copy number analysis, homozygosity analysis, and structural variant analysis also allowed us to precisely delineate the underlying pathogenic mechanisms, including gross deletion, uniparental heterodisomy, uniparental isodisomy, or imprinting defect. Furthermore, we showed allele-specific methylation in imprinting-related differentially methylated regions on chromosomes 6, 7, 11, 14, and 20 in a normal individual together with 4 Prader-Willi patients and 3 Angelman syndrome patients. Hence, presently reported method is likely to be applicable to the diagnosis of imprinting disorders other than Prader-Willi syndrome and Angelman syndrome as well.

Molecular basis of carotid body tumor and associated clinical features in Japan identified by genomic, immunohistochemical, and clinical analyses.

Carotid body tumor (CBT) is classified as a paraganglioma (PGL). Here, we report the genetic background, protein expression pattern, and clinical findings of 30 Japanese CBT cases. Germline pathogenic or likely pathogenic (P/LP) variants of genes encoding succinate dehydrogenase subunits (SDHs) were detected in 15 of 30 cases (50%). The SDHB variants were the most frequently detected, followed by SDHA and SDHD variants. One case with SDHAF2 variant was bilateral CBT, and other two multiple PGL cases were not detected P/LP variants. The three cases with germline variants that could be tested did not have somatic P/LP variants of the same genes. Immunohistochemical analysis showed negative SDHB signals in CBT tissues in five cases with germline P/LP variants of SDHB, SDHD, or SDHA. In addition, SDHB signals in CBT tissues were negative in four of nine cases without germline P/LP variants of SDHs. These findings suggest the involvement of unidentified molecular mechanisms affecting SDHs.

Utility of tissue-specific gene expression scores for gene prioritization in Mendelian diseases.

In genetic testing of Mendelian diseases, it is a bioinformatics challenge to effectively prioritize disease-causing candidate genes listed from massively parallel sequencing. Tissue specificity of the gene expression levels may give a clue because it may reflect tissue-specific disease manifestation. However, considering poor correlations between mRNA and protein expression in some genes, it is not clear whether transcriptomics- or proteomics-based tissue specificity should be used to prioritize candidate genes. Therefore, we compared the efficiency of tissue-specific scores (TS scores) obtained from transcriptome and proteome data in prioritizing candidate genes for whole exome sequencing (WES) analysis of Mendelian disease patients. We show that both Protein and RNA TS scores are useful in prioritizing candidate genes in WES analysis, although diseases like coagulopathies get more benefit from Protein TS score. This study may provide useful evidence in developing new methods to effectively identify novel disease-causing genes.