Hyon J. Kim

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.

Clinical and genetic characteristics of Korean patients with Gaucher disease.

Gaucher disease (GD) is an autosomal recessive glycolipid lysosomal storage disease caused by a deficiency of the β-glucocerebrosidase enzyme (GBA). Allelic heterogeneity in GD has been well described. To date, more than 270 different GBA mutations have been reported. In order to determine the GBA mutation spectrum in Korean GD patients, we performed GBA mutation analysis of Korean patients and identified 72 GBA mutant alleles from 36 unrelated patients (100% identification), including 60 single-nucleotide substitutions, 6 single-nucleotide deletions, 4 recombinants, 1 splicing error, and 1 complex allele. N370S, the most common GBA mutation, was not detected, and most of the Korean GBA mutations were previously known to be rare, with the exception of L444P (~21%). Three mutations, P201H, F347L+L444P, and c.630delC, are novel. Examination of the GBA mutant alleles found in 6 ethnic groups revealed that the prevalences of GBA mutant alleles in Korean patients are very different from those seen in Jewish, non-Jewish Caucasian, and Italian patients, but similar to those seen in Japanese and Chinese patients. Our data may provide greater understanding of GBA allelic heterogeneity and an Asian perspective(1) on correlations between genotypes and phenotypes, which may help further the development of better management strategies for patients with GD.

The Spectrum of NF1 Mutations in Korean Patients with Neurofibromatosis Type 1

Neurofibromatosis type 1 (NF1) is one of the most common autosomal dominant disorders in humans. NF1 is caused by mutations in the NF1 gene which consists of 57 exons and encodes a GTPase activating protein (GAP), neurofibromin. To date, more than 640 different NF1 mutations have been identified and registered in the Human Gene Mutation Database (HGMD). In order to assess the NF1 mutational spectrum in Korean NF1 patients, we screened 23 unrelated Korean NF1 patients for mutations in the coding region and splice sites of the NF1 gene. We have identified 21 distinct NF1 mutations in 22 patients. The mutations included 10 single base substitutions (3 missense and 7 nonsense), 10 splice site mutations, and 1 single base deletion. Eight mutations have been previously identified and thirteen mutations were novel. The mutations are evenly distributed across exon 3 through intron 47 of the NF1 gene and no mutational hot spots were found. This analysis revealed a wide spectrum of NF1 mutations in Korean patients. A genotype-phenotype correlation analysis suggests that there is no clear relationship between specific NF1 mutations and clinical features of the disease.

A case of Birt-Hogg-Dubé syndrome.

Birt-Hogg-Dubé syndrome (BHDS) is an autosomal dominant genodermatosis characterized by cutaneous hair follicle tumors (fibrofolliculoma or trichodiscoma), pulmonary cysts, and increased risk of renal neoplasia. The genetic alteration for BHDS has been mapped to chromosome 17p12q11, and the gene in this region has been cloned and believed to be responsible for the BHDS. Mutations in the BHD gene (also known as FLCN) have been described in the patients with BHDS. We present a case of a 30-yr-old Korean woman with multiple mildly pruritic papules on her face and neck area. The patient had several firm, flesh-colored, dome-shaped, papular lesions measuring between 2 to 5 mm. Except for a history of pneumothorax her medical records were not remarkable. Mutation analysis of the BHD gene was performed, and a novel deletion mutation (p.F519LfsX17 [c.1557delT]) causing truncation of the gene product, folliculin, was found in the exon 14. The actual incidence of BHDS is unknown, but it is most likely underdiagnosed. So it is imperative that doctors recognize the skin lesions of BHDS and institute proper screening to detect other manifestations of the disease. Here, we report a case of BHDS with a novel mutation, which is the first report in Korea.

Fragile X syndrome in Korea: a case series and a review of the literature.

The purposes of this study were to present DNA analysis findings of our case series of fragile X syndrome (FXS) based on methylation-specific polymerase chain reaction (MS-PCR), PCR, and Southern blotting alongside developmental characteristics including psychological profiles and to review the literature on FXS in Korea. The reports of 65 children (male:female, 52:13; age, 6.12±4.00 yrs) referred for the diagnosis of FXS over a 26-months period were retrospectively reviewed for the identification of full mutation or premutation of fragile X mental retardation 1 (FMR1). Among the 65 children, there were 4 boys with full mutation, and one boy showed premutation of FMR1, yielding a 6.15% positive rate of FXS. All 4 children with full mutation showed significant developmental delay, cognitive dysfunction, and varying degrees of autistic behaviors. The boys with premutation showed also moderate mental retardation, severe drooling, and behavioral problems as severe as the boys with full mutation. Thirteen articles on FXS in Korea have been published since 1993, and they were reviewed. The positive rate of FXS was in the range of 0.77-8.51%, depending on the study groups and the method of diagnosis. Finally, the population-based prevalence study on FXS in Korea is required in the near future.

Acute myeloid leukemia with t(16;21)(q24;q22) and eosinophilia: case report and review of the literature

The t(16;21)(q24;q22), a rare chromosomal translocation involving chromosome 21 in de novo and therapy-related acute myeloid leukemia (AML), produces a RUNX1-CBFA2T3 fusion gene (previously AML1-MTG16) fusion gene. The translocation has been reported in 20 patients with AML, with eosinophilia present in 3 cases. Here we report a pediatric case of t(16;21)(q24;q22) in de novo AML with eosinophilia and suggest that eosinophilia is a hematologic characteristic of at least a subpopulation of AML with t(16;21)(q24;q22). A 4-year-old Korean girl was admitted with complaints of pale appearance and dizziness, and was diagnosed with acute myelomonocytic leukemia. On admission, laboratory evaluation revealed hemoglobin at 3.3 g/dL, platelets at 9.0 x 10(9)/L, and white blood cells at 9.1 x 10(9)/L with 10% eosinophils and 1% blasts. The bone marrow aspirate contained 31% blasts and 11% eosinophils. Flow cytometric analysis revealed the expression of CD13, CD14, CD19, CD33, CD34, and HLA-DR by the leukemic blasts. The karyotype was 47,XX, + 8,t(16;21)(q24;q22)[18]/46,XX[2]. Interphase fluorescence in situ hybridization analysis with a dual-color, dual-fusion translocation LSI AML1/ETO probe set for RUNX1 and RUNX1T1 produced three signals for each probe in 90% of interphases, but no fusion signals. We confirmed the presence of RUNX1-CBFA2T3 fusion transcripts with reverse transcriptase-polymerase chain reaction, using primers AML1ex5f1 and MTG16r2.

Inhibition of Bcl-xL by ABT-737 enhances chemotherapy sensitivity in neurofibromatosis type 1-associated malignant peripheral nerve sheath tumor cells

Neurofibromatosis type 1 (NF1) is one of the most commonly inherited autosomal dominant disorders. The malignant peripheral nerve sheath tumor (MPNST) is a major cause of mortality in patients with NF1. In this study, we found that overexpression of Bcl-xL in the established NF1-associated MPNST cell line and primary tissue cultured MPNST cells derived from an NF1 patient was closely associated with anticancer drug resistance of the NF1-associated MPNST cells. We demonstrated that high expression of Bcl-xL in the MPNST cells was caused by a decreased transcriptional expression of the NF1 gene. Downregulation of the NF1 gene by RNA interference (RNAi) induced an increase in Bcl-xL expression and a decrease in its sensitivity to apoptosis in the benign neurofibroma cell line and primary normal cells. These results suggest that an alteration of Bcl-xL expression levels by somatic expression changes in the NF1 locus may contribute to the malignant development of benign tumor tissues or normal tissues to MPNSTs. We further demonstrated that either depletion of Bcl-xL expression by RNAi or inactivation of Bcl-xL by ABT-737, a mimetic of the BH3-only protein BAD, was very effective in sensitizing the MPNST cells to apoptotic cell death by combined treatment with the tested anticancer drug doxorubicin. Notably, a low concentration of ABT-737 and doxorubicin could effectively induce synergistic cytotoxicity in the MPNST cells. These results suggest that pharmacological inhibition of Bcl-xL by ABT-737 in combination with doxorubicin can be a potential therapeutic strategy for the treatment of NF1-associated MPNSTs.

A novel homozygous MMP2 mutation in a patient with Torg-Winchester syndrome.

Torg–Winchester syndrome (OMIM 259600) is an autosomal recessive multicentric osteolysis disorder. Mutations in the gene for matrix metalloproteinase 2 (MMP2) are involved in its pathogenesis. This is the first report of Torg–Winchester syndrome in east Asians. A 31-year-old female Korean patient had the typical clinical phenotypes of the syndrome, including shortening of trunk and limbs and severe osteolysis resulting in extremely small hands and feet. In addition, she had cord compression at the cervico-medullary junction, as well as lumbar dural ectasia. Molecular analysis revealed a novel homozygous missense mutation of MMP2, c.1217G>A (p.G406D). Gelatin zymography demonstrated a complete loss of the MMP2 activity of the mutation. Our results provide insights into the clinical and radiological features and pathogenic mechanisms of the syndrome.

Cochlear implantation and connexin expression in the child with keratitis-ichthyosis-deafness syndrome.

We report one child with keratitis-ichthyosis-deafness (KID) syndrome. The child showed sparse, short scalp and body hairs, ichthyotic skin, bilateral sensorineural hearing loss, and visual loss. These are associated with a nucleotide substitution, 148G>A, which results in amino acid change in codon 50 of gap junctional protein connexin (Cx) 26. Immunohistochemistry of skins showed up-regulation of Cx26 and down-regulation of Cx43. He has benefited from cochlear implantation for hearing even though low visual function and skin problems with high risk of infections. This is the very rare report about Cx expression in skins and cochlear implantation in KID syndrome.

Genetic Counseling in Korean Health Care System

Over the years Korean health care system has improved in delivery of quality care to the general population for many areas of the health problems. The system is now being recognized in the world as the most cost effective one. It is covered by the uniform national health insurance policy for which most people in Korea are mandatory policy holders. Genetic counseling service, however, which is well recognized as an integral part of clinical genetics service deals with diagnosis and management of genetic condition as well as genetic information presentation and family support, is yet to be delivered in comprehensive way for the patients and families in need. Two major obstacles in providing genetic counseling service in korean health care system are identified; One is the lack of recognition for the need for genetic counseling service as necessary service by the national health insurance. Genetic counseling consumes a significant time in delivery and the current very low-fee schedule for physician service makes it very difficult to provide meaningful service. Second is the critical shortage of qualified professionals in the field of medical genetics and genetic counseling who can provide the service of genetic counseling in clinical setting. However, recognition and understanding of the fact that the scope and role of genetic counseling is expanding in post genomic era of personalized medicine for delivery of quality health care, will lead to the efforts to overcome obstacles in providing genetic counseling service in korean health care system. Only concerted efforts from health care policy makers of government on clinical genetics service and genetic counseling for establishing adequate reimbursement coverage and professional communities for developing educational program and certification process for professional genetic counselors, are necessary for the delivery of much needed clinical genetic counseling service in Korea.