The Korean Genetic Diagnosis Program for Rare Disease (KGDP) enrolled 1890 patients with rare diseases between March 2017 and October 2022. Children and adolescents accounted for the majority of the patients, and systemic disease was the most common presenting symptom. The exome-based virtual disease-specific multigene panel was the most frequently used analytical method, with an overall diagnostic yield of 33.3%. A total of 629 positive cases were diagnosed, involving 297 genes. All 297 genes identified in these cases were confirmed to be known genes listed in the OMIM database. The nationwide KGDP network and its cooperation with the Korean Undiagnosed Diseases Program (KUDP) provide a more comprehensive genetic analysis of undiagnosed cases. The partnership between the KGDP and KUDP has the potential to improve the diagnosis and treatment options for patients. In conclusion, KGDP serves as the primary access point or gateway to KUDP.

Germline mutations in MBD4, which, like MUTYH and NTHL1, encodes a glycosylase of the DNA based excision repair system, cause an autosomal recessive syndrome characterised by increased risk of acute myeloid leukaemia, gastrointestinal polyposis, colorectal cancer (CRC) and, to a lesser extent, uveal melanoma and schwannomas. To better define the phenotypic spectrum and tumour molecular features associated with biallelic MBD4-associated cancer predisposition, and study if heterozygous variants are associated with gastrointestinal tumour predisposition, we evaluated germline MBD4 status in 728 patients with CRC, polyposis, and other suggestive phenotypes (TCGA and in-house cohorts). Eight CRC patients carried rare homozygous or heterozygous germline variants in MBD4. The information gathered on mode of inheritance, variant nature, functional effect of the variant, and tumour mutational characteristics suggested that none of the patients included in the study had an MBD4-associated hereditary syndrome and that the heterozygous variants identified were not associated with the disease.

The prevalence of pathogenic and likely pathogenic (P/LP) variants in genes associated with cancer predisposition syndromes (CPS) is estimated to be 8-18% for paediatric cancer patients. In more than half of the carriers, the family history is unsuspicious for CPS. Therefore, broad genetic testing could identify germline predisposition in additional children with cancer resulting in important implications for themselves and their families. We thus evaluated clinical trio genome sequencing (TGS) in a cohort of 72 paediatric patients with solid cancers other than retinoblastoma or CNS-tumours. The most prevalent cancer types were sarcoma (n = 26), neuroblastoma (n = 15), and nephroblastoma (n = 10). Overall, P/LP variants in CPS genes were identified in 18.1% of patients (13/72) and P/LP variants in autosomal-dominant CPS genes in 9.7% (7/72). Genetic evaluation would have been recommended for the majority of patients with P/LP variants according to the Jongmans criteria. Four patients (5.6%, 4/72) carried P/LP variants in autosomal-dominant genes known to be associated with their tumour type. With the immediate information on variant inheritance, TGS facilitated the identification of a de novo P/LP in NF1, a gonadosomatic mosaic in WT1 and two pathogenic variants in one patient (DICER1 and PALB2). TGS allows a more detailed characterization of structural variants with base-pair resolution of breakpoints which can be relevant for the interpretation of copy number variants. Altogether, TGS allows comprehensive identification of children with a CPS and supports the individualised clinical management of index patients and high-risk relatives.

Thinness and anorexia nervosa are both characterised by persistent low weight. Individuals with anorexia nervosa concurrently report distorted perceptions of their body and engage in weight-loss behaviours, whereas individuals with thinness often wish to gain weight. Both conditions are heritable and share genomics with BMI, but are not genetically correlated with each other. Based on their pattern of genetic associations with other traits, we explored differences between thinness and anorexia nervosa on a genomic level. In Part 1, using publicly available data, we compared genetic correlations of persistent thinness/anorexia nervosa with eleven psychiatric disorders. In Part 2, we identified individuals with adolescent persistent thinness in the Avon Longitudinal Study of Parents and Children (ALSPAC) by latent class growth analysis of measured BMI from 10 to 24 years (n = 6594) and evaluated associations with psychiatric and anthropometric polygenic scores. In Part 1, in contrast to the positive genetic correlations of anorexia nervosa with various psychiatric disorders, persistent thinness showed negative genetic correlations with attention deficit hyperactivity disorder (rgAN = 0.08 vs. rgPT = -0.30), alcohol dependence (rgAN = 0.07 vs. rgPT = -0.44), major depressive disorder (rgAN = 0.27 vs. rgPT = -0.18) and post-traumatic stress disorder (rgAN = 0.26 vs. rgPT = -0.20). In Part 2, individuals with adolescent persistent thinness in the ALSPAC had lower borderline personality disorder polygenic scores (OR = 0.77; Q = 0.01). Overall, results suggest that genetic variants associated with thinness are negatively associated with psychiatric disorders and therefore thinness may be differentiable from anorexia nervosa on a genomic level.

Pathogenic variants impacting upon assembly of mitochondrial respiratory chain Complex IV (Cytochrome c Oxidase or COX) predominantly result in early onset mitochondrial disorders often leading to CNS, skeletal and cardiac muscle manifestations. The aim of this study is to describe a molecular defect in the COX assembly factor gene COX18 as the likely cause of a neonatal form of mitochondrial encephalo-cardio-myopathy and axonal sensory neuropathy. The proband is a 19-months old female displaying hypertrophic cardiomyopathy at birth and myopathy with axonal sensory neuropathy and failure to thrive developing in the first months of life. Serum lactate was consistently increased. Whole exome sequencing allowed the prioritization of the unreported homozygous substitution NM_001297732.2:c.667 G > C p.(Asp223His) in COX18. Patient's muscle biopsy revealed severe and diffuse COX deficiency and striking mitochondrial abnormalities. Biochemical and enzymatic studies in patient's myoblasts and in HEK293 cells after COX18 silencing showed a severe impairment of both COX activity and assembly. The biochemical defect was partially rescued by delivery of wild-type COX18 cDNA into patient's myoblasts. Our study identifies a novel defect of COX assembly and expands the number of nuclear genes involved in a mitochondrial disorder due to isolated COX deficiency.

Neurofibromatosis 1 (NF1) is a multisystem disorder associated with, for example, a high risk for cancer, a variety of behavioral and cognitive deficits, low educational attainment and decreased income. We now examined the labor market participation of individuals with NF1. We analyzed the numbers of days of work, unemployment, and sickness allowance among 742 Finnish individuals with NF1 aged 20-59 years using nationwide register data from Statistics Finland and the Social Insurance Institution of Finland. The individuals with NF1 were compared with a control cohort of 8716 individuals matched with age, sex, and the area of residence. Individuals with NF1 had a significantly lower number of working days per year than the controls (rate ratio [RR] 0.93, 95% CI 0.91-0.95). Unemployment (RR 1.79, 95% CI 1.58-2.02), and sickness absence (RR 1.44, 95% CI 1.25-1.67) were more frequent in the NF1 than in the control group. The causes of sickness allowances were highly concordant with the previously reported morbidity profile of NF1 including neoplasms, cardiovascular disease, mental and behavioral diseases, and neurological diseases. In conclusion, NF1 significantly interferes with labor market participation via both unemployment and morbidity. Unemployment seems to cause more days of not working than sickness absence.

Nemaline myopathy (NM) is a heterogeneous genetic neuromuscular disorder characterized by rod bodies in muscle fibers resulting in multiple complications due to muscle weakness. NM patients and their families could benefit from genetic analysis for early diagnosis, carrier and prenatal testing; however, clinical classification of variants is subject to change as further information becomes available. Reclassification can significantly alter the clinical management of patients and their families. We used the newly published data and ACMG/AMP guidelines to reassess NM-associated variants previously reported by clinical laboratories (ClinVar). Our analyses on rare variants that were not canonical loss-of-function (LOF) resulted in the downgrading of ~29% (28/97) of variants from pathogenic or likely-pathogenic (P/LP) to variants of uncertain significance (VUS). In addition, we analyzed the splicing effect of variants identified in NM patients by clinical laboratories or research, using an accurate in silico prediction tool that applies a deep-learning network. We identified 55 rare variants that may impact splicing (cryptic splicing). We also analyzed six new NM families and identified eight variants in NEB and ACTA1, including three novel variants: homozygous pathogenic c.164A > G (p.Tyr55Cys), and homozygous likely pathogenic c.980T > C (p.Met327Thr) in ACTA1, and heterozygous VUS c.18694-3T > G in NEB. This study demonstrates the importance of reclassifying variants to facilitate more definitive "calls" on causality or no causality in clinical genetic testing of patients with NM. Reclassification of ~150 variants is now available for improved clinical management, risk counseling and screening of NM patients.

Niemann-Pick type C1 disease (NPC1 [OMIM 257220]) is a rare and severe autosomal recessive disorder, characterized by a multitude of neurovisceral clinical manifestations and a fatal outcome with no effective treatment to date. Aiming to gain insights into the genetic aspects of the disease, clinical, genetic, and biomarker PPCS data from 602 patients referred from 47 countries and diagnosed with NPC1 in our laboratory were analyzed. Patients' clinical data were dissected using Human Phenotype Ontology (HPO) terms, and genotype-phenotype analysis was performed. The median age at diagnosis was 10.6 years (range 0-64.5 years), with 287 unique pathogenic/likely pathogenic (P/LP) variants identified, expanding NPC1 allelic heterogeneity. Importantly, 73 P/LP variants were previously unpublished. The most frequent variants detected were: c.3019C > G, p.(P1007A), c.3104C > T, p.(A1035V), and c.2861C > T, p.(S954L). Loss of function (LoF) variants were significantly associated with earlier age at diagnosis, highly increased biomarker levels, and a visceral phenotype (abnormal abdomen and liver morphology). On the other hand, the variants p.(P1007A) and p.(S954L) were significantly associated with later age at diagnosis (p < 0.001) and mildly elevated biomarker levels (p ≤ 0.002), consistent with the juvenile/adult form of NPC1. In addition, p.(I1061T), p.(S954L), and p.(A1035V) were associated with abnormality of eye movements (vertical supranuclear gaze palsy, p ≤ 0.05). We describe the largest and most heterogenous cohort of NPC1 patients published to date. Our results suggest that besides its utility in variant classification, the biomarker PPCS might serve to indicate disease severity/progression. In addition, we establish new genotype-phenotype relationships for "frequent" NPC1 variants.