Displaying publications 1 - 20 of 21 in total

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  1. 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.
  2. 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.
  3. GRIN2D variants in three cases of developmental and epileptic encephalopathy
    Tsuchida N, Hamada K, Shiina M, Kato M, Kobayashi Y, Tohyama J, et al.
    Clin Genet, 2018 12;94(6):538-547.
    PMID: 30280376 DOI: 10.1111/cge.13454
    N-methyl-d-aspartate (NMDA) receptors are glutamate-activated ion channels that are widely distributed in the central nervous system and essential for brain development and function. Dysfunction of NMDA receptors has been associated with various neurodevelopmental disorders. Recently, a de novo recurrent GRIN2D missense variant was found in two unrelated patients with developmental and epileptic encephalopathy. In this study, we identified by whole exome sequencing novel heterozygous GRIN2D missense variants in three unrelated patients with severe developmental delay and intractable epilepsy. All altered residues were highly conserved across vertebrates and among the four GluN2 subunits. Structural consideration indicated that all three variants are probably to impair GluN2D function, either by affecting intersubunit interaction or altering channel gating activity. We assessed the clinical features of our three cases and compared them to those of the two previously reported GRIN2D variant cases, and found that they all show similar clinical features. This study provides further evidence of GRIN2D variants being causal for epilepsy. Genetic diagnosis for GluN2-related disorders may be clinically useful when considering drug therapy targeting NMDA receptors.
  4. Compound heterozygous mutations in TTC7A cause familial multiple intestinal atresias and severe combined immunodeficiency
    Yang W, Lee PP, Thong MK, Ramanujam TM, Shanmugam A, Koh MT, et al.
    Clin Genet, 2015 Dec;88(6):542-9.
    PMID: 25534311 DOI: 10.1111/cge.12553
    Familial multiple intestinal atresias is an autosomal recessive disease with or without combined immunodeficiency. In the last year, several reports have described mutations in the gene TTC7A as causal to the disease in different populations. However, exact correlation between different genotypes and various phenotypes are not clear. In this study, we report identification of novel compound heterozygous mutations in TTC7A gene in a Malay girl with familial multiple intestinal atresias and severe combined immunodeficiency (MIA-SCID) by whole exome sequencing. We found two mutations in TTC7A: one that destroyed a putative splicing acceptor at the junction of intron 17/exon 18 and one that introduced a stop codon that would truncate the last two amino acids of the encoded protein. Reviewing the recent reports on TTC7A mutations reveals correlation between the position and nature of the mutations with patient survival and clinical manifestations. Examination of public databases also suggests carrier status for healthy individuals, making a case for population screening on this gene, especially in populations with suspected frequent founder mutations.
  5. Whole exome sequencing is an efficient, sensitive and specific method for determining the genetic cause of short-rib thoracic dystrophies
    McInerney-Leo AM, Harris JE, Leo PJ, Marshall MS, Gardiner B, Kinning E, et al.
    Clin Genet, 2015 Dec;88(6):550-7.
    PMID: 25492405 DOI: 10.1111/cge.12550
    Short-rib thoracic dystrophies (SRTDs) are congenital disorders due to defects in primary cilium function. SRTDs are recessively inherited with mutations identified in 14 genes to date (comprising 398 exons). Conventional mutation detection (usually by iterative Sanger sequencing) is inefficient and expensive, and often not undertaken. Whole exome massive parallel sequencing has been used to identify new genes for SRTD (WDR34, WDR60 and IFT172); however, the clinical utility of whole exome sequencing (WES) has not been established. WES was performed in 11 individuals with SRTDs. Compound heterozygous or homozygous mutations were identified in six confirmed SRTD genes in 10 individuals (IFT172, DYNC2H1, TTC21B, WDR60, WDR34 and NEK1), giving overall sensitivity of 90.9%. WES data from 993 unaffected individuals sequenced using similar technology showed two individuals with rare (minor allele frequency <0.005) compound heterozygous variants of unknown significance in SRTD genes (specificity >99%). Costs for consumables, laboratory processing and bioinformatic analysis were
  6. Frequent occurrence of gastric cancer in Asian kindreds with Li-Fraumeni syndrome
    Ariffin H, Chan AS, Oh L, Abd-Ghafar S, Ong GB, Mohamed M, et al.
    Clin Genet, 2015 Nov;88(5):450-5.
    PMID: 25318593 DOI: 10.1111/cge.12525
    Type of cancer and age of onset in individuals with inherited aberrations in the tumour suppressor gene TP53 are variable, possibly influenced by genetic modifiers and different environmental exposure. Since 2009, the modified Chompret criteria (MCC) have been used to identify individuals for TP53 mutation screening. Using the TP53 mutation database maintained by the International Agency for Research on Cancer (IARC), we investigated if the MCC, mainly developed for a Caucasian population, was also applicable in Asia. We identified several differences in Asian families compared with similar Caucasian cohorts, suggesting that identification and management of Li-Fraumeni syndrome in Asia do not completely mirror that of North America and Western Europe. Early gastric cancer (<40 years) may be considered a new addition to the MCC especially for Asian families.
  7. Identification of a recurrent BRCA1 exon 21-22 genomic rearrangement in Malay breast cancer patients
    Hasmad HN, Sivanandan K, Lee V, Yip CH, Mohd Taib NA, Teo SH
    Clin Genet, 2015 Apr;87(4):392-4.
    PMID: 25066186 DOI: 10.1111/cge.12451
  8. Childhood adrenocortical carcinoma as a sentinel cancer for detecting families with germline TP53 mutations
    Choong SS, Latiff ZA, Mohamed M, Lim LL, Chen KS, Vengidasan L, et al.
    Clin Genet, 2012 Dec;82(6):564-8.
    PMID: 22233476 DOI: 10.1111/j.1399-0004.2012.01841.x
    Li-Fraumeni syndrome (LFS) is a highly penetrant, autosomal dominant disorder where affected individuals carry a 50% risk of developing cancer before 30 years of age. It is most commonly associated with mutations in the tumour suppressor gene, TP53. Adrenocortical carcinoma (ACC) is a very rare paediatric cancer, and up to 80% of affected children are found to carry germline TP53 mutations. Hence, we propose using childhood ACC incidence as selection criteria for referral for TP53 mutation testing, independent of familial cancer history. Under the auspices of the Malaysian Society of Paediatric Haematology-Oncology, four eligible children diagnosed with ACC over a 30-month study period were referred for mutation testing. Three had a germline TP53 mutation. Subsequent TP53 testing in relatives showed two inherited mutations and one de novo mutation. These findings strongly support paediatric ACC as a useful sentinel cancer for initiating a germline TP53/LFS detection programme, particularly in countries where the lack of structured oncogenetic practice precludes the identification of families with LFS features.
  9. Prevalence and ethnic differences of autosomal-dominant cerebellar ataxia in Singapore
    Zhao Y, Tan EK, Law HY, Yoon CS, Wong MC, Ng I
    Clin Genet, 2002 Dec;62(6):478-81.
    PMID: 12485197
    We report the prevalence and ethnic differences of autosomal-dominant cerebellar ataxia (ADCA) in Singapore. Amongst 204 patients with ataxia who underwent genetic testing for dentatorubral-pallidoluysian atrophy (DRPLA) and for spinocerebellar ataxias (SCA) 1, 2, 3, 6, 7, 8, 10 and 12, 58 (28.4%) patients from 36 families tested positive. SCA 3 was identified in 31 (53.4%) patients from 15 families, SCA 2 in 17 (29.3%) patients from 12 families and SCA 1 in four (6.9%) patients from four families. Other SCA subtypes were rare. SCA 2 was the only subtype identified amongst ethnic Malay and ethnic Indian families. The estimated prevalence of ADCA in Singaporean families was at least 1 : 27,000. Based on the history and ancestry of Singaporeans, our study supported a founder effect for specific SCA subtypes and the association of ethnicity-specific SCA subtypes. Our findings suggest that SCA 2 is relatively common amongst the Malay race and that priority testing for SCA 3 and SCA 2 for ethnic Chinese, and SCA 2 for ethnic Malay, may be cost effective and relevant for the region.
  10. Distribution of alpha1-antitrypsin PI S and PI Z frequencies in countries outside Europe: a meta-analysis
    Blanco I, Bustillo EF, Rodriguez MC
    Clin Genet, 2001 Dec;60(6):431-41.
    PMID: 11846735
    The objective of the present study was to review published surveys on allelic frequencies S and Z in countries outside Europe to evaluate the validity of the reported data. Studies on the topic, published from 1965 to May 2001, were retrieved using MEDLINE and bibliographic reference consultations. The criteria for the selection of the studies were the following: 1) sample size >or=250 individuals; 2) alpha1-antitrypsin phenotype determination performed by means of crossed antigen-antibody, isoelectric focusing in polyacrylamide gels, or polymerase chain reaction (PCR); 3) PI type determination performed without any previous screening procedure; 4) S and Z 95% CI of the reported outcomes within the limits of a calculated coefficient of variation. Forty-three out of 85 studies comply with the established criteria for being analysed. Worldwide maps of geographical distributions of PI S and PI Z frequencies have been designed by the authors by adding the data provided by these 43 selected studies to the 70 reported in a recent European meta-analysis.
  11. Low-density lipoprotein receptor gene mutations in a Southeast Asian population with familial hypercholesterolemia
    Khoo KL, van Acker P, Defesche JC, Tan H, van de Kerkhof L, Heijnen-van Eijk SJ, et al.
    Clin Genet, 2000 Aug;58(2):98-105.
    PMID: 11005141 DOI: 10.1034/j.1399-0004.2000.580202.x
    The aim of this study was to detect mutations in the genes coding for the low-density lipoprotein receptor and apolipoprotein B in patients of Southeast Asian origin with clinically diagnosed familial hypercholesterolemia (FH) and to relate these findings with the observed lower incidence of coronary heart disease in this part of the world. A total of 86 unrelated patients with FH were selected on clinical grounds, and complete DNA analysis of the low-density lipoprotein (LDL)-receptor and apolipoprotein B (apoB) genes by DGGE and DNA-sequencing was performed. In the majority (73%) of the cohort studied, no mutations could be detected, even after extensive analysis of the LDL-receptor and apoB genes. However, the 22 patients with a mutation had significantly more xanthomas and a higher incidence of coronary heart disease and levels of low-density lipoproteins were also significantly different. There was no correlation between the type of the mutation and lipoprotein levels or clinical signs of atherosclerosis. The fact that the majority of the FH patients studied had no detectable mutation and that this group had a significant milder phenotype, suggests the presence of a third gene in the Southeast Asian population, predominantly leading to a disorder resembling a milder form of FH. A similar, but less frequent, trait has recently been described in a number of European families.
  12. Down syndrome associated with a retroperitoneal teratoma and Morgagni hernia
    Quah BS, Menon BS
    Clin Genet, 1996 Oct;50(4):232-4.
    PMID: 9001806
    Down syndrome may be associated with many complications. Among the malignancies associated with Down syndrome, leukaemia is the most common. This is a case report of a patient with Down syndrome associated with both a retroperitoneal teratoma and a Morgagni hernia.
  13. The current state of diagnostic genetics for conditions affecting sex development
    Alhomaidah D, McGowan R, Ahmed SF
    Clin Genet, 2017 02;91(2):157-162.
    PMID: 28127758 DOI: 10.1111/cge.12912
    Disorders of sex development (DSD), are a group of rare congenital conditions. Unlike 46, XX DSD where the cause is usually clear, identification of a cause of XY DSD is often unclear and may be attributed to a disorder of gonadal development, androgen synthesis or androgen action. Reaching a firm diagnosis is challenging and requires expertise within a framework that abides by the highest standards of clinical care. Whilst conditions associated with altered sex development have improved our fundamental understanding of sex and gonadal development, it is debatable whether this improvement in our understanding has improved the lives of people with DSD. Thus, there is a need for more emphasis on showing that a firm diagnosis for conditions associated with DSD is associated with a change in clinical practice that benefits the patient. With the rapid advances in diagnostic technology, there is also a need for clearer guidance on the relative merits of biochemical vs genetic evaluation. The standardization and harmonization of complex genetic and biochemical analyses for rare conditions are issues that require further guidance and it is probably that international networks and registries for rare conditions will facilitate the development of this framework.
  14. DEPDC5 mutations in familial and sporadic focal epilepsy
    Tsai MH, Chan CK, Chang YC, Yu YT, Chuang ST, Fan WL, et al.
    Clin Genet, 2017 Oct;92(4):397-404.
    PMID: 28170089 DOI: 10.1111/cge.12992
    BACKGROUND AND AIMS: Mutations in the disheveled, Egl-10 and pleckstrin domain-containing protein 5 (DEPDC5) gene have emerged as an important cause of various familial focal epilepsy syndromes. However, the significance of DEPDC5 mutations in patients with sporadic focal epilepsy has yet to be characterized.

    MATERIALS AND METHODS: We studied a kindred of familial focal epilepsy with variable foci using whole-exome sequencing. We subsequently studied a cohort of 293 patients with focal epilepsy and sequenced all exons of DEPDC5 using targeted resequencing.

    RESULTS: We reported a Taiwanese family with a novel splice site mutation which affected mRNA splicing and activated the downstream mammalian target of rapamycin (mTOR) pathway. Among patients with focal epilepsies, the majority (220/293) of these patients had sporadic focal epilepsy without malformation of cortical development. Two (0.9%) of these patients had probably pathogenic mutations in the DEPDC5 gene.

    DISCUSSION AND CONCLUSIONS: Our finding suggests that DEPDC5 is not only the most common gene for familial focal epilepsy but also could be a significant gene for sporadic focal epilepsy. Since focal epilepsies account for more than 60% of all epilepsies, the effect of mTORC1 inhibitor on patients with focal epilepsy due to DEPDC5 mutations will be an important future direction of research.

  15. Fulltext A homozygous missense variant in CHRM3 associated with familial urinary bladder disease
    Beaman GM, Galatà G, Teik KW, Urquhart JE, Aishah A, O'Sullivan J, et al.
    Clin Genet, 2019 12;96(6):515-520.
    PMID: 31441039 DOI: 10.1111/cge.13631
    CHRM3 codes for the M3 muscarinic acetylcholine receptor that is located on the surface of smooth muscle cells of the detrusor, the muscle that effects urinary voiding. Previously, we reported brothers in a family affected by a congenital prune belly-like syndrome with mydriasis due to homozygous CHRM3 frameshift variants. In this study, we describe two sisters with bladders that failed to empty completely and pupils that failed to constrict fully in response to light, who are homozygous for the missense CHRM3 variant c.352G > A; p.(Gly118Arg). Samples were not available for genotyping from their brother, who had a history of multiple urinary tract infections and underwent surgical bladder draining in the first year of life. He died at the age of 6 years. This is the first independent report of biallelic variants in CHRM3 in a family with a rare serious bladder disorder associated with mydriasis and provides important evidence of this association.
  16. Identification of germline alterations in breast cancer predisposition genes among Malaysian breast cancer patients using panel testing
    Ng PS, Wen WX, Fadlullah MZ, Yoon SY, Lee SY, Thong MK, et al.
    Clin Genet, 2016 10;90(4):315-23.
    PMID: 26757417 DOI: 10.1111/cge.12735
    Although an association between protein-truncating variants and breast cancer risk has been established for 11 genes, only alterations in BRCA1, BRCA2, TP53 and PALB2 have been reported in Asian populations. Given that the age of onset of breast cancer is lower in Asians, it is estimated that inherited predisposition to breast cancer may be more significant. To determine the potential utility of panel testing, we investigated the prevalence of germline alterations in 11 established and 4 likely breast cancer genes in a cross-sectional hospital-based cohort of 108 moderate to high-risk breast cancer patients using targeted next generation sequencing. Twenty patients (19%) were identified to carry deleterious mutations, of whom 13 (12%) were in the BRCA1 or BRCA2, 6 (6%) were in five other known breast cancer predisposition genes and 1 patient had a mutation in both BRCA2 and BARD1. Our study shows that BRCA1 and BRCA2 account for the majority of genetic predisposition to breast cancer in our cohort of Asian women. Although mutations in other known breast cancer genes are found, the functional significance and breast cancer risk have not yet been determined, thus limiting the clinical utility of panel testing in Asian populations.
  17. Mutation analysis of genes within the dynactin complex in a cohort of hereditary peripheral neuropathies
    Tey S, Ahmad-Annuar A, Drew AP, Shahrizaila N, Nicholson GA, Kennerson ML
    Clin Genet, 2016 Aug;90(2):127-33.
    PMID: 26662454 DOI: 10.1111/cge.12712
    The cytoplasmic dynein-dynactin genes are attractive candidates for neurodegenerative disorders given their functional role in retrograde transport along neurons. The cytoplasmic dynein heavy chain (DYNC1H1) gene has been implicated in various neurodegenerative disorders, and dynactin 1 (DCTN1) genes have been implicated in a wide spectrum of disorders including motor neuron disease, Parkinson's disease, spinobulbar muscular atrophy and hereditary spastic paraplegia. However, the involvement of other dynactin genes with inherited peripheral neuropathies (IPN) namely, hereditary sensory neuropathy, hereditary motor neuropathy and Charcot-Marie-Tooth disease is under reported. We screened eight genes; DCTN1-6 and ACTR1A and ACTR1B in 136 IPN patients using whole-exome sequencing and high-resolution melt (HRM) analysis. Eight non-synonymous variants (including one novel variant) and three synonymous variants were identified. Four variants have been reported previously in other studies, however segregation analysis within family members excluded them from causing IPN in these families. No variants of disease significance were identified in this study suggesting the dynactin genes are unlikely to be a common cause of IPNs. However, with the ease of querying gene variants from exome data, these genes remain worthwhile candidates to assess unsolved IPN families for variants that may affect the function of the proteins.
  18. Pathogenic variants in the survival of motor neurons complex gene GEMIN5 cause cerebellar atrophy
    Saida K, Tamaoki J, Sasaki M, Haniffa M, Koshimizu E, Sengoku T, et al.
    Clin Genet, 2021 12;100(6):722-730.
    PMID: 34569062 DOI: 10.1111/cge.14066
    Cerebellar ataxia is a genetically heterogeneous disorder. GEMIN5 encoding an RNA-binding protein of the survival of motor neuron complex, is essential for small nuclear ribonucleoprotein biogenesis, and it was recently reported that biallelic loss-of-function variants cause neurodevelopmental delay, hypotonia, and cerebellar ataxia. Here, whole-exome analysis revealed compound heterozygous GEMIN5 variants in two individuals from our cohort of 162 patients with cerebellar atrophy/hypoplasia. Three novel truncating variants and one previously reported missense variant were identified: c.2196dupA, p.(Arg733Thrfs*6) and c.1831G > A, p.(Val611Met) in individual 1, and c.3913delG, p.(Ala1305Leufs*14) and c.4496dupA, p.(Tyr1499*) in individual 2. Western blotting analysis using lymphoblastoid cell lines derived from both affected individuals showed significantly reduced levels of GEMIN5 protein. Zebrafish model for null variants p.(Arg733Thrfs*6) and p.(Ala1305Leufs*14) exhibited complete lethality at 2 weeks and recapitulated a distinct dysplastic phenotype. The phenotypes of affected individuals and the zebrafish mutant models strongly suggest that biallelic loss-of-function variants in GEMIN5 cause cerebellar atrophy/hypoplasia.
  19. Multicenter study on the genetics of glomerular diseases among southeast and south Asians: Deciphering Diversities - Renal Asian Genetics Network (DRAGoN)
    Lu L, Yap YC, Nguyen DQ, Chan YH, Ng JL, Zhang YC, et al.
    Clin Genet, 2022 Jan 22.
    PMID: 35064937 DOI: 10.1111/cge.14116
    Multinational studies have reported monogenic etiologies in 25%-30% of children with steroid-resistant nephrotic syndrome. Such large studies are lacking in Asia. We established Deciphering Diversities: Renal Asian Genetics Network (DRAGoN) and aimed to describe the genetic and clinical spectrums in Asians. We prospectively studied a cohort of 183 probands with suspected genetic glomerulopathies from South and Southeast Asia, of whom 17% had positive family history. Using multi-gene panel sequencing, we detected pathogenic variants in 26 (14%) probands, of whom one-third had COL4A4 or COL4A5 variants (n = 9, 5%). Of those with COL4A5 defects, only 25% had features suggestive of Alport syndrome. Besides traditional predictors for genetic disease (positive family history and extrarenal malformations), we identified novel predictors, namely older age (6.2 vs. 2.4 years; p = 0.001), hematuria (OR 5.6; 95% CI 2.1-14.8; p 60% when a second risk factor (positive family history or extrarenal manifestation) co-existed. The genetic spectrum of glomerulopathies appears different in Asia. Collagen IV genes may be included in sequencing panels even when suggestive clinical features are absent.
  20. Expanding the phenotype of PPP1R21-related neurodevelopmental disorder
    Almannai M, Marafi D, Zaki MS, Maroofian R, Efthymiou S, Saadi NW, et al.
    Clin Genet, 2024 Feb 14.
    PMID: 38356149 DOI: 10.1111/cge.14492
    PPP1R21 encodes for a conserved protein that is involved in endosomal maturation. Biallelic pathogenic variants in PPP1R21 have been associated with a syndromic neurodevelopmental disorder from studying 13 affected individuals. In this report, we present 11 additional individuals from nine unrelated families and their clinical, radiological, and molecular findings. We identified eight different variants in PPP1R21, of which six were novel variants. Global developmental delay and hypotonia are neurological features that were observed in all individuals. There is also a similar pattern of dysmorphic features with coarse faces as a gestalt observed in several individuals. Common findings in 75% of individuals with available brain imaging include delays in myelination, wavy outline of the bodies of the lateral ventricles, and slight prominence of the bodies of the lateral ventricles. PPP1R21-related neurodevelopmental disorder is associated with a consistent phenotype and should be considered in highly consanguineous individuals presenting with developmental delay/intellectual disability along with coarse facial features.
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