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Fulltext Identification of two novel mutations, PSEN1 E280K and PRNP G127S, in a Malaysian family

Ch'ng GS, An SS, Bae SO, Bagyinszky E, Kim S

Neuropsychiatr Dis Treat, 2015;11:2315-22.
PMID: 26396515 DOI: 10.2147/NDT.S86334

Alzheimer's disease (AD) is the most common form of dementia, which can be categorized into two main forms: early onset AD and late onset AD. The genetic background of early onset AD is well understood, and three genes, the APP, PSEN1, and PSEN2 have been identified as causative genes. In the current study, we tested three siblings from Malaysia who were diagnosed with early onset dementia, as well as their available family members. The family history was positive as their deceased father was similarly affected. Patients were tested for mutations in APP, PSEN1, PSEN2, and PRNP. A novel variant, E280K, was discovered in exon 8 of PSEN1 in the three siblings. In silico analyses with SIFT, SNAP, and PolyPhen2 prediction tools and three-dimensional modeling were performed, and the results suggested that the mutation is probably a pathogenic variant. Two additional pathogenic mutations were previously been described for codon 280, E280A, and E280G, which could support the importance of the E280 residue in the PS1 protein contributing to the pathogenic nature of E280K. Additional ten family members were screened for the E280K mutation, and all of them were negative. Six of them presented with a variety of neuropsychiatric symptoms, including learning disabilities, epilepsy, and schizophrenia, while four family members were asymptomatic. A novel PRNP G127S mutation was found in a step-niece of the three siblings harboring the PSEN1 E280K mutation. In silico predictions for PRNP G127S mutation suggested that this might be possibly a damaging variant. Additional studies to characterize PRNP G127S would be necessary to further understand the effects of this mutation.
Maternal gonosomal mosaicism in rare autosomal dominant SLFN14-related thrombocytopenia

Ang MP, Yeoh SL, Lim CH, Foo SL, Wong YW, Ch'ng GS

Br J Haematol, 2022 Dec;199(5):765-767.
PMID: 36237120 DOI: 10.1111/bjh.18481
Novel biallelic SZT2 mutations in 3 cases of early-onset epileptic encephalopathy

Tsuchida N, Nakashima M, Miyauchi A, Yoshitomi S, Kimizu T, Ganesan V, et al.

Clin Genet, 2018 02;93(2):266-274.
PMID: 28556953 DOI: 10.1111/cge.13061

The seizure threshold 2 (SZT2) gene encodes a large, highly conserved protein that is associated with epileptogenesis. In mice, Szt2 is abundantly expressed in the central nervous system. Recently, biallelic SZT2 mutations were found in 7 patients (from 5 families) presenting with epileptic encephalopathy with dysmorphic features and/or non-syndromic intellectual disabilities. In this study, we identified by whole-exome sequencing compound heterozygous SZT2 mutations in 3 patients with early-onset epileptic encephalopathies. Six novel SZT2 mutations were found, including 3 truncating, 1 splice site and 2 missense mutations. The splice-site mutation resulted in skipping of exon 20 and was associated with a premature stop codon. All individuals presented with seizures, severe developmental delay and intellectual disabilities with high variability. Brain MRIs revealed a characteristic thick and short corpus callosum or a persistent cavum septum pellucidum in each of the 2 cases. Interestingly, in the third case, born to consanguineous parents, had unexpected compound heterozygous missense mutations. She showed microcephaly despite the other case and previous ones presenting with macrocephaly, suggesting that SZT2 mutations might affect head size.
A novel homozygous truncating variant of NECAP1 in early infantile epileptic encephalopathy: the second case report of EIEE21

Mizuguchi T, Nakashima M, Moey LH, Ch'ng GS, Khoo TB, Mitsuhashi S, et al.

J Hum Genet, 2019 Apr;64(4):347-350.
PMID: 30626896 DOI: 10.1038/s10038-018-0556-2

We report the second case of early infantile epileptic encephalopathy (EIEE) arising from a homozygous truncating variant of NECAP1. The boy developed infantile-onset tonic-clonic and tonic seizures, then spasms in clusters. His electroencephalogram (EEG) showed a burst suppression pattern, leading to the diagnosis of Ohtahara syndrome. Whole-exome sequencing revealed the canonical splice-site variant (c.301 + 1 G > A) in NECAP1. In rodents, Necap1 protein is enriched in neuronal clathrin-coated vesicles and modulates synaptic vesicle recycling. cDNA analysis confirmed abnormal splicing that produced early truncating mRNA. There has been only one previous report of a mutation in NECAP1 in a family with EIEE; this was a nonsense mutation (p.R48*) that was cited as EIEE21. Decreased mRNA levels and the loss of the WXXF motif in both the families suggests that loss of NECAP1 function is a common pathomechanism for EIEE21. This study provided additional support that synaptic vesicle recycling plays a key role in epileptogenesis.
Fulltext Cost-Effectiveness of Colorectal Cancer Genetic Testing

Ramdzan AR, Manaf MRA, Aizuddin AN, Latiff ZA, Teik KW, Ch'ng GS, et al.

Int J Environ Res Public Health, 2021 08 06;18(16).
PMID: 34444091 DOI: 10.3390/ijerph18168330

Colorectal cancer (CRC) remains the second leading cause of cancer-related deaths worldwide. Approximately 3-5% of CRCs are associated with hereditary cancer syndromes. Individuals who harbor germline mutations are at an increased risk of developing early onset CRC, as well as extracolonic tumors. Genetic testing can identify genes that cause these syndromes. Early detection could facilitate the initiation of targeted prevention strategies and surveillance for CRC patients and their families. The aim of this study was to determine the cost-effectiveness of CRC genetic testing. We utilized a cross-sectional design to determine the cost-effectiveness of CRC genetic testing as compared to the usual screening method (iFOBT) from the provider's perspective. Data on costs and health-related quality of life (HRQoL) of 200 CRC patients from three specialist general hospitals were collected. A mixed-methods approach of activity-based costing, top-down costing, and extracted information from a clinical pathway was used to estimate provider costs. Patients and family members' HRQoL were measured using the EQ-5D-5L questionnaire. Data from the Malaysian Study on Cancer Survival (MySCan) were used to calculate patient survival. Cost-effectiveness was measured as cost per life-year (LY) and cost per quality-adjusted life-year (QALY). The provider cost for CRC genetic testing was high as compared to that for the current screening method. The current practice for screening is cost-saving as compared to genetic testing. Using a 10-year survival analysis, the estimated number of LYs gained for CRC patients through genetic testing was 0.92 years, and the number of QALYs gained was 1.53 years. The cost per LY gained and cost per QALY gained were calculated. The incremental cost-effectiveness ratio (ICER) showed that genetic testing dominates iFOBT testing. CRC genetic testing is cost-effective and could be considered as routine CRC screening for clinical practice.
Hyperexcretion of homocitrulline in a Malaysian patient with lysinuric protein intolerance

Habib A, Md Yunus Z, Azize NA, Ch'ng GS, Ong WP, Chen BC, et al.

Eur J Pediatr, 2013 Sep;172(9):1277-81.
PMID: 23358709 DOI: 10.1007/s00431-013-1947-1

Lysinuric protein intolerance (LPI; MIM 222700) is an inherited aminoaciduria with an autosomal recessive mode of inheritance. Biochemically, affected patients present with increased excretion of the cationic amino acids: lysine, arginine, and ornithine. We report the first case of LPI diagnosed in Malaysia presented with excessive excretion of homocitrulline. The patient was a 4-year-old male who presented with delayed milestones, recurrent diarrhea, and severe failure to thrive. He developed hyperammonemic coma following a forced protein-rich diet. Plasma amino acid analysis showed increased glutamine, alanine, and citrulline but decreased lysine, arginine and ornithine. Urine amino acids showed a marked excretion of lysine and ornithine together with a large peak of unknown metabolite which was subsequently identified as homocitrulline by tandem mass spectrometry. Molecular analysis confirmed a previously unreported homozygous mutation at exon 1 (235 G > A, p.Gly79Arg) in the SLC7A7 gene. This report demonstrates a novel mutation in the SLC7A7 gene in this rare inborn error of diamino acid metabolism. It also highlights the importance of early and efficient treatment of infections and dehydration in these patients.
CONCLUSION: The diagnosis of LPI is usually not suspected by clinical findings alone, and specific laboratory investigations and molecular analysis are important to get a definitive diagnosis.
Fulltext PLPBP mutations cause variable phenotypes of developmental and epileptic encephalopathy

Shiraku H, Nakashima M, Takeshita S, Khoo CS, Haniffa M, Ch'ng GS, et al.

Epilepsia Open, 2018 Dec;3(4):495-502.
PMID: 30525118 DOI: 10.1002/epi4.12272

Objective: Vitamin B6-dependent epilepsies are treatable disorders caused by variants in several genes, such as ALDH7A1,PNPO, and others. Recently, biallelic variants in PLPBP, formerly known as PROSC, were identified as a novel cause of vitamin B6-dependent epilepsies. Our objective was to further delineate the phenotype of PLPBP mutation.
Methods: We identified 4 unrelated patients harboring a total of 4 variants in PLPBP, including 3 novel variants, in a cohort of 700 patients with developmental and epileptic encephalopathies. Clinical information in each case was collected.
Results: Each patient had a different clinical course of epilepsy, with seizure onset from the first day of life to 3 months of age. Generalized tonic-clonic seizures were commonly noted. Myoclonic seizures or focal seizures were also observed in 2 patients. Interictal electroencephalography showed variable findings, such as suppression burst, focal or multifocal discharges, and diffuse slow activity. Unlike previous reports, all the patients had some degree of intellectual disability, although some of them had received early treatment with vitamin B6, suggesting that different mutation types influence the severity and outcome of the seizures.
Significance: PLPBP variants should be regarded as among the causative genes of developmental and epileptic encephalopathy, even when it occurs after the neonatal period. Early diagnosis and proper treatment with pyridoxine or pyridoxal phosphate is essential to improve the neurologic prognosis in neonates or young children with poorly controlled seizures.
Mainstreaming genetic counselling for genetic testing of BRCA1 and BRCA2 in ovarian cancer patients in Malaysia (MaGiC study)

Yoon SYY, Ahmad Bashah NS, Wong SW, Mariapun S, Padmanabhan H, Hassan T, et al.

Ann Oncol, 2018 Nov;29 Suppl 9:ix176.
PMID: 32177935 DOI: 10.1093/annonc/mdy483.004
Fulltext Novel mutations associated with carnitine-acylcarnitine translocase and carnitine palmitoyl transferase 2 deficiencies in Malaysia

Habib A, Azize NAA, Rahman SA, Yakob Y, Suberamaniam V, Nazri MIBA, et al.

Clin Biochem, 2021 Dec;98:48-53.
PMID: 34626609 DOI: 10.1016/j.clinbiochem.2021.10.002

OBJECTIVE: Carnitine-acylcarnitine Translocase (CACT) deficiency (OMIM 212138) and carnitine palmitoyl transferase 2 (CPT2) deficiency (OMIM 60065050) are rare inherited disorders of mitochondrial long chain fatty acid oxidation. The aim of our study is to review the clinical, biochemical and molecular characteristics in children diagnosed with CACT and CPT2 deficiencies in Malaysia.
DESIGN AND METHODS: This is a retrospective study. We reviewed medical records of six patients diagnosed with CACT and CPT2 deficiencies. They were identified from a selective high-risk screening of 50,579 patients from January 2010 until Jun 2020.
RESULTS: All six patients had either elevation of the long chain acylcarnitines and/or an elevated (C16 + C18:1)/C2 acylcarnitine ratio. SLC25A20 gene sequencing of patient 1 and 6 showed a homozygous splice site mutation at c.199-10 T > G in intron 2. Two novel mutations at c.109C > T p. (Arg37*) in exon 2 and at c.706C > T p. (Arg236*) in exon 7 of SLC25A20 gene were found in patient 2. Patient 3 and 4 (siblings) exhibited a compound heterozygous mutation at c.638A > G p. (Asp213Gly) and novel mutation c.1073 T > G p. (Leu358Arg) in exon 4 of CPT2 gene. A significant combined prevalence at 0.01% of CACT and CPT2 deficiencies was found in the symptomatic Malaysian patients.
CONCLUSIONS: The use of the (C16 + C18:1)/C2 acylcarnitine ratio in dried blood spot in our experience improves the diagnostic specificity for CACT/CPT2 deficiencies over long chain acylcarnitine (C16 and C18:1) alone. DNA sequencing for both genes aids in confirming the diagnosis.
Detection of copy number variations in epilepsy using exome data

Tsuchida N, Nakashima M, Kato M, Heyman E, Inui T, Haginoya K, et al.

Clin Genet, 2018 03;93(3):577-587.
PMID: 28940419 DOI: 10.1111/cge.13144

Epilepsies are common neurological disorders and genetic factors contribute to their pathogenesis. Copy number variations (CNVs) are increasingly recognized as an important etiology of many human diseases including epilepsy. Whole-exome sequencing (WES) is becoming a standard tool for detecting pathogenic mutations and has recently been applied to detecting CNVs. Here, we analyzed 294 families with epilepsy using WES, and focused on 168 families with no causative single nucleotide variants in known epilepsy-associated genes to further validate CNVs using 2 different CNV detection tools using WES data. We confirmed 18 pathogenic CNVs, and 2 deletions and 2 duplications at chr15q11.2 of clinically unknown significance. Of note, we were able to identify small CNVs less than 10 kb in size, which might be difficult to detect by conventional microarray. We revealed 2 cases with pathogenic CNVs that one of the 2 CNV detection tools failed to find, suggesting that using different CNV tools is recommended to increase diagnostic yield. Considering a relatively high discovery rate of CNVs (18 out of 168 families, 10.7%) and successful detection of CNV with <10 kb in size, CNV detection by WES may be able to surrogate, or at least complement, conventional microarray analysis.
Fulltext De Novo Truncating Variants in the Last Exon of SEMA6B Cause Progressive Myoclonic Epilepsy

Hamanaka K, Imagawa E, Koshimizu E, Miyatake S, Tohyama J, Yamagata T, et al.

Am J Hum Genet, 2020 04 02;106(4):549-558.
PMID: 32169168 DOI: 10.1016/j.ajhg.2020.02.011

De novo variants (DNVs) cause many genetic diseases. When DNVs are examined in the whole coding regions of genes in next-generation sequencing analyses, pathogenic DNVs often cluster in a specific region. One such region is the last exon and the last 50 bp of the penultimate exon, where truncating DNVs cause escape from nonsense-mediated mRNA decay [NMD(-) region]. Such variants can have dominant-negative or gain-of-function effects. Here, we first developed a resource of rates of truncating DNVs in NMD(-) regions under the null model of DNVs. Utilizing this resource, we performed enrichment analysis of truncating DNVs in NMD(-) regions in 346 developmental and epileptic encephalopathy (DEE) trios. We observed statistically significant enrichment of truncating DNVs in semaphorin 6B (SEMA6B) (p value: 2.8 × 10-8; exome-wide threshold: 2.5 × 10-6). The initial analysis of the 346 individuals and additional screening of 1,406 and 4,293 independent individuals affected by DEE and developmental disorders collectively identified four truncating DNVs in the SEMA6B NMD(-) region in five individuals who came from unrelated families (p value: 1.9 × 10-13) and consistently showed progressive myoclonic epilepsy. RNA analysis of lymphoblastoid cells established from an affected individual showed that the mutant allele escaped NMD, indicating stable production of the truncated protein. Importantly, heterozygous truncating variants in the NMD(+) region of SEMA6B are observed in general populations, and SEMA6B is most likely loss-of-function tolerant. Zebrafish expressing truncating variants in the NMD(-) region of SEMA6B orthologs displayed defective development of brain neurons and enhanced pentylenetetrazole-induced seizure behavior. In summary, we show that truncating DNVs in the final exon of SEMA6B cause progressive myoclonic epilepsy.
Clinical and biochemical features of aromatic L-amino acid decarboxylase deficiency

Brun L, Ngu LH, Keng WT, Ch'ng GS, Choy YS, Hwu WL, et al.

PMID: 20505134 DOI: 10.1212/WNL.0b013e3181e620ae

Neurology. 2010 Jul 6;75(1):64-71
OBJECTIVE: To describe the current treatment; clinical, biochemical, and molecular findings; and clinical follow-up of patients with aromatic l-amino acid decarboxylase (AADC) deficiency.
METHOD: Clinical and biochemical data of 78 patients with AADC deficiency were tabulated in a database of pediatric neurotransmitter disorders (JAKE). A total of 46 patients have been previously reported; 32 patients are described for the first time.
RESULTS: In 96% of AADC-deficient patients, symptoms (hypotonia 95%, oculogyric crises 86%, and developmental retardation 63%) became clinically evident during infancy or childhood. Laboratory diagnosis is based on typical CSF markers (low homovanillic acid, 5-hydroxyindoleacidic acid, and 3-methoxy-4-hydroxyphenolglycole, and elevated 3-O-methyl-l-dopa, l-dopa, and 5-hydroxytryptophan), absent plasma AADC activity, or elevated urinary vanillactic acid. A total of 24 mutations in the DDC gene were detected in 49 patients (8 reported for the first time: p.L38P, p.Y79C, p.A110Q, p.G123R, p.I42fs, c.876G>A, p.R412W, p.I433fs) with IVS6+ 4A>T being the most common one (allele frequency 45%).
CONCLUSION: Based on clinical symptoms, CSF neurotransmitters profile is highly indicative for the diagnosis of aromatic l-amino acid decarboxylase deficiency. Treatment options are limited, in many cases not beneficial, and prognosis is uncertain. Only 15 patients with a relatively mild form clearly improved on a combined therapy with pyridoxine (B6)/pyridoxal phosphate, dopamine agonists, and monoamine oxidase B inhibitors.
Oncologist-led BRCA counselling improves access to cancer genetic testing in middle-income Asian country, with no significant impact on psychosocial outcomes

Yoon SY, Wong SW, Lim J, Ahmad S, Mariapun S, Padmanabhan H, et al.

J Med Genet, 2022 Mar;59(3):220-229.
PMID: 33526602 DOI: 10.1136/jmedgenet-2020-107416

BACKGROUND: Identifying patients with BRCA mutations is clinically important to inform on the potential response to treatment and for risk management of patients and their relatives. However, traditional referral routes may not meet clinical needs, and therefore, mainstreaming cancer genetics has been shown to be effective in some high-income and high health-literacy settings. To date, no study has reported on the feasibility of mainstreaming in low-income and middle-income settings, where the service considerations and health literacy could detrimentally affect the feasibility of mainstreaming.
METHODS: The Mainstreaming Genetic Counselling for Ovarian Cancer Patients (MaGiC) study is a prospective, two-arm observational study comparing oncologist-led and genetics-led counselling. This study included 790 multiethnic patients with ovarian cancer from 23 sites in Malaysia. We compared the impact of different method of delivery of genetic counselling on the uptake of genetic testing and assessed the feasibility, knowledge and satisfaction of patients with ovarian cancer.
RESULTS: Oncologists were satisfied with the mainstreaming experience, with 95% indicating a desire to incorporate testing into their clinical practice. The uptake of genetic testing was similar in the mainstreaming and genetics arm (80% and 79%, respectively). Patient satisfaction was high, whereas decision conflict and psychological impact were low in both arms of the study. Notably, decisional conflict, although lower than threshold, was higher for the mainstreaming group compared with the genetics arm. Overall, 13.5% of patients had a pathogenic variant in BRCA1 or BRCA2, and there was no difference between psychosocial measures for carriers in both arms.
CONCLUSION: The MaGiC study demonstrates that mainstreaming cancer genetics is feasible in low-resource and middle-resource Asian setting and increased coverage for genetic testing.
Fulltext Mutations in KEOPS-complex genes cause nephrotic syndrome with primary microcephaly

Braun DA, Rao J, Mollet G, Schapiro D, Daugeron MC, Tan W, et al.

Nat Genet, 2017 Oct;49(10):1529-1538.
PMID: 28805828 DOI: 10.1038/ng.3933

Galloway-Mowat syndrome (GAMOS) is an autosomal-recessive disease characterized by the combination of early-onset nephrotic syndrome (SRNS) and microcephaly with brain anomalies. Here we identified recessive mutations in OSGEP, TP53RK, TPRKB, and LAGE3, genes encoding the four subunits of the KEOPS complex, in 37 individuals from 32 families with GAMOS. CRISPR-Cas9 knockout in zebrafish and mice recapitulated the human phenotype of primary microcephaly and resulted in early lethality. Knockdown of OSGEP, TP53RK, or TPRKB inhibited cell proliferation, which human mutations did not rescue. Furthermore, knockdown of these genes impaired protein translation, caused endoplasmic reticulum stress, activated DNA-damage-response signaling, and ultimately induced apoptosis. Knockdown of OSGEP or TP53RK induced defects in the actin cytoskeleton and decreased the migration rate of human podocytes, an established intermediate phenotype of SRNS. We thus identified four new monogenic causes of GAMOS, describe a link between KEOPS function and human disease, and delineate potential pathogenic mechanisms.
Genomic analyses in Cornelia de Lange Syndrome and related diagnoses: Novel candidate genes, genotype-phenotype correlations and common mechanisms

Kaur M, Blair J, Devkota B, Fortunato S, Clark D, Lawrence A, et al.

Am J Med Genet A, 2023 Aug;191(8):2113-2131.
PMID: 37377026 DOI: 10.1002/ajmg.a.63247

Cornelia de Lange Syndrome (CdLS) is a rare, dominantly inherited multisystem developmental disorder characterized by highly variable manifestations of growth and developmental delays, upper limb involvement, hypertrichosis, cardiac, gastrointestinal, craniofacial, and other systemic features. Pathogenic variants in genes encoding cohesin complex structural subunits and regulatory proteins (NIPBL, SMC1A, SMC3, HDAC8, and RAD21) are the major pathogenic contributors to CdLS. Heterozygous or hemizygous variants in the genes encoding these five proteins have been found to be contributory to CdLS, with variants in NIPBL accounting for the majority (>60%) of cases, and the only gene identified to date that results in the severe or classic form of CdLS when mutated. Pathogenic variants in cohesin genes other than NIPBL tend to result in a less severe phenotype. Causative variants in additional genes, such as ANKRD11, EP300, AFF4, TAF1, and BRD4, can cause a CdLS-like phenotype. The common role that these genes, and others, play as critical regulators of developmental transcriptional control has led to the conditions they cause being referred to as disorders of transcriptional regulation (or "DTRs"). Here, we report the results of a comprehensive molecular analysis in a cohort of 716 probands with typical and atypical CdLS in order to delineate the genetic contribution of causative variants in cohesin complex genes as well as novel candidate genes, genotype-phenotype correlations, and the utility of genome sequencing in understanding the mutational landscape in this population.

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