Chong Kun Cheon

Clinical implementation of whole-genome array CGH as a first-tier test in 5080 pre and postnatal cases

BackgroundArray comparative genomic hybridization (CGH) is currently the most powerful method for detecting chromosomal alterations in pre and postnatal clinical cases. In this study, we developed a BAC based array CGH analysis platform for detecting whole genome DNA copy number changes including specific micro deletion and duplication chromosomal disorders. Additionally, we report our experience with the clinical implementation of our array CGH analysis platform. Array CGH was performed on 5080 pre and postnatal clinical samples from patients referred with a variety of clinical phenotypes.ResultsA total of 4073 prenatal cases (4033 amniotic fluid and 40 chorionic villi specimens) and 1007 postnatal cases (407 peripheral blood and 600 cord blood) were studied with complete concordance between array CGH, karyotype and fluorescence in situ hybridization results. Among 75 positive prenatal cases with DNA copy number variations, 60 had an aneuploidy, seven had a deletion, and eight had a duplication. Among 39 positive postnatal cases samples, five had an aneuploidy, 23 had a deletion, and 11 had a duplication.ConclusionsThis study demonstrates the utility of using our newly developed whole-genome array CGH as first-tier test in 5080 pre and postnatal cases. Array CGH has increased the ability to detect segmental deletion and duplication in patients with variable clinical features and is becoming a more powerful tool in pre and postnatal diagnostics.

Practical approach to steroid 5alpha-reductase type 2 deficiency

The aim of this article is to review the literature on steroid 5alpha-reductase type 2 deficiency (5α-RD2) to provide clinicians with information to guide their management of patients with this disorder. The 5alpha-reductase type 2 is encoded by the 5alpha-reductase type 2 gene (SRD5A2) on chromosome 2 and is predominantly expressed in external genital tissues and the prostate. Mutations of the SRD5A2 gene leads to an uncommon autosomal recessive disorder affecting sexual differentiation in individuals with 46,XY karyotype; their phenotype can range from almost normal female structures to a distinct male phenotype with ambiguous genitalia at birth. These phenotypes result from impaired conversion of testosterone to dihydrotestosterone due to mutations in the SRD5A2 gene. Patients exhibit virilization at puberty without breast development, which is often accompanied by gender identity change from female to male. More than 40 mutations have been reported in all five exons of the SRD5A2 gene. Phenotype–genotype correlations for 5α-RD2 have not been well established. The newborn phenotypes of male pseudohermaphrodites with 5α-RD2, partial androgen insensitivity syndrome (PAIS), or 17β-hydroxysteroid dehydrogenase type 3 (17β-HSD3) enzyme deficiency may be indistinguishable. We conclude that steroid 5α-RD2 should be included in the differential diagnosis of newborns with 46,XY DSD. It is important that the diagnosis be made in infancy by biochemical and molecular studies before gender assignment or any surgical intervention because these patients should be considered males at birth.

Identification of KMT2D and KDM6A mutations by exome sequencing in Korean patients with Kabuki syndrome

Kabuki syndrome (KS) (OMIM#147920) is a multiple congenital anomaly/mental retardation syndrome. Recently, pathogenic variants in KMT2D and KDM6A were identified as the causes of KS in 55.8–80.0% of patients. To elucidate further the molecular characteristics of Korean patients with KS, we screened a cohort of patients with clinically defined KS for mutations in KMT2D and KDM6A. Whole-exome sequencing and direct sequencing for validation were performed in 12 patients with a clinical suspicion of KS. KMT2D and KDM6A mutations were identified in 11 (91.7%) patients. No recurrent mutation was observed, and 10 out of the 11 mutations found were novel. KMT2D mutations were detected in 10 patients, including four small deletions or insertions and four nonsense and two missense mutations. One girl had a novel splice-site mutation in KDM6A. Each patient had a unique individual mutation. This is the first report of mutational analysis via exome sequencing in Korean patients with KS. Because the mutation-detection rate was high in this study, rigorous mutation analysis of KMT2D and KDM6A may be an important tool for the early diagnosis and genetic counseling of Korean patients with KS.

The common exon 3 polymorphism of the growth hormone receptor gene and the effect of growth hormone therapy on growth in Korean patients with Turner syndrome.

Objective  Recombinant human growth hormone (GH) can achieve final adult height gain in girls with Turner syndrome (TS), but its efficacy varies widely across individuals. The exon 3‐deleted polymorphism of growth hormone receptor (d3‐GHR) has been reported to be associated with responsiveness to GH therapy. The short‐term growth response of Turner patients to GH therapy was analysed according to their GHR‐exon 3 polymorphism genotype.

Novel Mutation in SLC6A19 Causing Late-Onset Seizures in Hartnup Disorder

Hartnup disorder is caused by an inborn error of neutral amino acid transport in the kidneys and intestines. It is characterized by pellagra-like rash, ataxia, and psychotic behavior. Elevated urinary neutral amino acids are the first indicator of the disorder. SLC6A19 was identified as the causative gene in autosomal-recessive Hartnup disorder, which encodes the amino acid transporter B(0)AT1, mediating neutral amino acid transport from the luminal compartment to the intracellular space. Here, we report on a Korean boy aged 8 years and 5 months with Hartnup disorder, as confirmed by SLC6A19 gene analysis. He manifested seizures, attention-deficit hyperactivity disorder, and mental retardation without pellagra or ataxia. Multiple neutral amino acids were increased in his urine, and genetic analysis of SLC6A19 revealed compound heterozygous mutations, c.908C>T (p.Ser303Leu) and c.1787_1788insG (p.Thr596fsX73), both of which are novel. A novel SLC6A19 gene mutation was associated with late-onset seizures in a Korean patient with Hartnup disorder.

Clinical Characterization and Analysis of the SRD5A2 Gene in Six Korean Patients with 5α-Reductase Type 2 Deficiency

Aims: The aim of this study was to perform a 5α-reductase type 2 gene (SRD5A2) analysis in 6 Korean patients with external genitalia ranging from predominantly female to male in whom 5α-reductase type 2 deficiency was suspected. Patients: Six patients from five unrelated families participated, and all of their parents were non-consanguineous. Three patients presented with ambiguous genitalia at birth, and 2 were referred owing to delayed puberty. The other patient was presented incidentally during an operation for inguinal hernia. Basal and post-human chorionic gonadotropin-stimulated serum testosterone and dihydrotestosterone levels were determined, but neither the levels nor ratio yielded enough information for differential diagnosis. Confirmative diagnosis was achieved by SRD5A2 gene analysis. Results: Four different pathologic mutations were identified. All have already been reported, and are located in exon 1 (p.Q6X), exon 4 (p.G203S and c.655delT), and exon 5 (p.R246Q). p.R246Q was the most frequently identified mutation in our study, and c.655delT has been detected only in Korean patients to date. Conclusion: The molecular analysis is the most reliable method for a correct diagnosis of 5α-reductase type 2 deficiency. Identification of mutations also enables genetic counseling for families at risk.

A case of Antley-Bixler syndrome caused by compound heterozygous mutations of the cytochrome P450 oxidoreductase gene

Antley-Bixler syndrome (ABS) is a skeletal malformation syndrome primarily affecting the skull and limbs. Although causal mutations in the FGFR2 gene have been found in some patients, mutations in the electron donor enzyme P450 oxidoreductase gene (POR) have recently been found to cause ABS in other patients. In addition to skeletal malformations, POR deficiency also causes glucocorticoid deficiency and congenital adrenal hyperplasia with ambiguous genitalia in both sexes. Here, we report on a 7-month-old Korean girl with ABS and ambiguous genitalia who was confirmed by POR gene analysis. Our patient showed typical skeletal findings with brachycephaly, mid-face hypoplasia, and radiohumeral synostosis. She also had partial labial fusion and a single urogenital orifice, as well as increased 17α-hydroxyprogesterone levels, suggesting a 21-hydroxylase deficiency. Cortisol and DHEA-sulfate response to rapid adrenocorticotropic hormone (ACTH) stimulation was inadequate. Direct sequencing of the POR gene revealed compound heterozygous mutations (I444fsX449 and R457H). This is the first report of a Korean patient with ABS caused by POR gene mutations.

Genetics of Prader-Willi syndrome and Prader-Will-Like syndrome

The Prader-Willi syndrome (PWS) is a human imprinting disorder resulting from genomic alterations that inactivate imprinted, paternally expressed genes in human chromosome region 15q11-q13. This genetic condition appears to be a contiguous gene syndrome caused by the loss of at least 2 of a number of genes expressed exclusively from the paternal allele, including SNRPN, MKRN3, MAGEL2, NDN and several snoRNAs, but it is not yet well known which specific genes in this region are associated with this syndrome. Prader-Will-Like syndrome (PWLS) share features of the PWS phenotype and the gene functions disrupted in PWLS are likely to lie in genetic pathways that are important for the development of PWS phenotype. However, the genetic basis of these rare disorders differs and the absence of a correct diagnosis may worsen the prognosis of these individuals due to the endocrine-metabolic malfunctioning associated with the PWS. Therefore, clinicians face a challenge in determining when to request the specific molecular test used to identify patients with classical PWS because the signs and symptoms of PWS are common to other syndromes such as PWLS. This review aims to provide an overview of current knowledge relating to the genetics of PWS and PWLS, with an emphasis on identification of patients that may benefit from further investigation and genetic screening.

Kabuki syndrome: clinical and molecular characteristics

Kabuki syndrome (KS) is a rare syndrome characterized by multiple congenital anomalies and mental retardation. Other characteristics include a peculiar facial gestalt, short stature, skeletal and visceral abnormalities, cardiac anomalies, and immunological defects. Whole exome sequencing has uncovered the genetic basis of KS. Prior to 2013, there was no molecular genetic information about KS in Korean patients. More recently, direct Sanger sequencing and exome sequencing revealed KMT2D variants in 11 Korean patients and a KDM6A variant in one Korean patient. The high detection rate of KMT2D and KDM6A mutations (92.3%) is expected owing to the strict criteria used to establish a clinical diagnosis. Increased awareness and understanding of KS among clinicians is important for diagnosis and management of KS and for primary care of KS patients. Because mutation detection rates rely on the accuracy of the clinical diagnosis and the inclusion or exclusion of atypical cases, recognition of KS will facilitate the identification of novel mutations. A brief review of KS is provided, highlighting the clinical and genetic characteristics of patients with KS.

Clinical outcomes and the mutation spectrum of the OTC gene in patients with ornithine transcarbamylase deficiency

Ornithine transcarbamylase (OTC) deficiency is an X-linked inborn error of the urea cycle that leads to the accumulation of ammonia, resulting in neurological deficits. This study was performed to describe the clinical outcomes, biochemical features and molecular spectra of patients with OTC deficiency. A total of 49 patients from 47 unrelated Korean pedigrees were included who were diagnosed with OTC deficiency based on biochemical findings and molecular analyses. Patient clinical features, biochemical findings and molecular data were analyzed retrospectively. Males with neonatal-onset phenotype presented with seizure or altered mentality (n=20). Biochemical findings showed high blood ammonia (1132.5±851.6 μmol l−1) and urine orotic acid (1840.7±1731.3 mmol mol−1 Cr) levels. There were also five males with late-onset disease who presented with vomiting, irritability and seizure at age 8.2±9.4 years old (range, 0.6–20 years). Symptomatic females presented with vomiting, seizure, and altered mentality at age 3.5±3.5 years (range, 0.2–12.8 years; n=24). More males with the late-onset form and symptomatic females displayed mild hyperammonemia and orotic aciduria compared with those showing a neonatal phenotype (P<0.05). Molecular analysis identified 37 different mutations (22 missense, 5 large deletions, 4 small deletions, 1 insertion, 3 nonsense and 2 splice sites) from all 49 patients; the mutations were dispersed throughout all coding exons. In Korean patients with OTC deficiency, mutations in OTC are genetically heterogeneous. Male patients with the neonatal-onset phenotype showed poor outcomes because of severe hyperammonemia. Early diagnosis and interventions for hyperammonemia can provide more favorable prognosis.