Uniparental disomy (UPD) refers to a chromosome defect that an individual's homologous chromosome or segments are inherited from one parent. UPD can cause either aberrant patterns of genomic imprinting or homozygosity of mutations, leading to various diseases, including cancer. The mechanisms of UPD formation are diverse but largely due to the incorrect chromosome separation during cell division. UPD does not alter the number of gene copies, thus is difficult to be detected by conventional cytogenetic techniques effectively. Assisted by the new techniques such as single nucleotide polymorphism arrays, more and more UPD-related cases have been reported recently. UPD events are non-randomly distributed across cancer types, which play important role in the occurrence, development and metastasis of cancer. Here we review the research progress on the formation mechanisms, detection methods, the involved chromosomal regions and genes, and clinical significance of UPD; and also discuss the directions for future studies in this field.
Genomic Imprinting ; Humans ; Neoplasms ; genetics ; Research ; trends ; Uniparental Disomy

The overall prevalence of uniparental disomy (UPD) across all chromosomes was estimated to be around one birth in 2000. To date, more than 4170 UPD cases have been registered. UPD for chromosomes 6, 7, 11, 14, 15, and 20 can result in clinically recognizable imprinting disorders due to abnormal levels of imprinted gene expression. For other chromosomes, the clinical consequences associated with UPD are not apparent, unless when a recessive genetic disorder is unmasked by UPD or regions of homozygosity (ROH). A clinical practice guideline will assist in strengthening the precise analysis and interpretation of the clinical significance of ROH/UPD. This guideline summarizes the conception, mechanism and clinical consequences of ROH/UPD, as well as the principles for data analysis, with an aim to standardize the clinical application and data interpretation.
Gene Expression ; Genomic Imprinting ; Homozygote ; Humans ; Uniparental Disomy/genetics*

Constitutional trisomy 8 mosaicism (CT8M) is a relatively rare aneuploidy in humans with characteristic phenotypes including typical craniofacial feature (such as deformed skull, prominent forehead, low-set and/or dysplastic ears), skeletal malformation, cardiac anomaly, renal malformation, cryptochidism, varying degree of developemental delay. Due to the extremely variable phenotypic and cytogenetic expression, CT8M has gone undiagnosed in certain patients. We report a 28-year-old women with secondary amenorreha without characteristic CT8M phenotype. Chromosomal analysis showed a CT8M (47,XX,+8[9]/46,XX[41]).
Adult ; Aneuploidy ; Chromosomes, Human, Pair 8 ; Cytogenetics ; Female ; Forehead ; Humans ; Mosaicism ; Phenotype ; Skull ; Trisomy ; Uniparental Disomy

PURPOSE: Prader-Willi syndrome (PWS) is a well-known genetic disorder, and microdeletion on chromosome 15 is the most common causal mechanism. Several previous studies have suggested that various environmental factors might be related to the pathogenesis of microdeletion in PWS. In this study, we investigated birth seasonality in Korean PWS. METHODS: A total of 211 PWS patients born from 1980 to 2014 were diagnosed by methylation polymerase chain reaction at Samsung Medical Center. Of the 211 patients, 138 were born from 2000-2013. Among them, the 74 patients of a deletion group and the 22 patients of a maternal uniparental disomy (UPD) group were compared with general populations born from 2000 using the Walter and Elwood method and cosinor analysis. RESULTS: There was no statistical significance in seasonal variation in births of the total 211 patients with PWS (chi2=7.2522, P=0.2982). However, a significant difference was found in the monthly variation between PWS with the deletion group and the at-risk general population (P<0.05). In the cosinor model, the peak month of birth for PWS patients in the deletion group was January, while the nadir occurred in July, with statistical significance (amplitude=0.23, phase=1.2, low point=7.2). The UPD group showed the peak birth month in spring; however, this result was not statistically significant (chi2=3.39, P=0.1836). CONCLUSION: Correlation with birth seasonality was identified in a deletion group of Korean PWS patients. Further studies are required to identify the mechanism related to seasonal effects of environmental factors on microdeletion on chromosome 15.
Chromosomes, Human, Pair 15* ; Humans ; Methylation ; Parturition* ; Polymerase Chain Reaction ; Prader-Willi Syndrome* ; Seasons* ; Uniparental Disomy

OBJECTIVE: To explore the influence of uniparental disomy (UPD) on bipartite and tripartite paternity testing. METHODS: Two cases of paternity testing were analyzed by multiplex amplification and capillary electrophoresis typing. Suspected UPD was verified by using single nucleotide polymorphism array (SNP array). Parental power index was calculated by using a bipartite or tripartite model. RESULTS: The two cases were found to harbor respectively three short tandem repeats on chromosome 2 and two short tandem repeats on chromosome 15. SNP array verified that both cases were of UPD. Case 1 had a parental power index of 122274987565.23 by a tripartite model, while case 2 had a parental power index of 13500.8463 by a bipartite model. Based on the technical specification, the conclusions supported a biological parent-child relationship in both cases. CONCLUSION UPD may lead to misjudgment of paternity testing. The possibility of UPD should be considered when certain loci which do not conform to Mendelian inheritance have aggregated to one chromosome.
Chromosomes, Human, Pair 2 ; genetics ; Humans ; Microsatellite Repeats ; Paternity ; Polymorphism, Single Nucleotide ; Uniparental Disomy ; genetics

Infantile onset diabetes mellitus(especially, neonatal diabetes) is rare disorder and may be transient or permanent. Most patients are full-term but small-for-date infants and typical symptoms occur within the first 4-6 weeks of life, requiring insulin therapy. Neonatal diabetes differs from type 1 diabetes in many aspects and seems to form a distinct entity of inborn pancreatic malfunction. The transient cases often develop type 2 diabetes mellitus later in life. In recent reports, transient neonatal diabetes is associated with paternal uniparental isodisomy and unbalanced duplication of chromosome 6q22-23. In our study, clinical course of case 1 was compatible with transient neonatal diabetes, but chromosomal abnormalities such as above was not shown in DNA analysis. In case 2 and 3, we could not decide exactly on genetic basis.
Chromosome Aberrations ; Diabetes Mellitus, Type 1* ; Diabetes Mellitus, Type 2 ; DNA ; Genomic Imprinting* ; Humans ; Infant ; Insulin ; Uniparental Disomy

Chromosomal loss in trisomy (trisomy rescue) to generate a disomic fetus can cause confined placental mosaicism and/or feto/placental mosaicism. After trisomy rescue event, there is a risk of fetal uniparental disomy (UPD). Noninvasive prenatal test (NIPT) reflects the genomic constitution of the placenta, not of the fetus itself. Feto-placental discrepancy can therefore cause false-positive (trisomy) NIPT results. These discordant NIPT results can serve as important clues to find UPD associated with confined placental mosaicism. We report a case with maternal UPD of chromosome 20, detected by NIPT of 1,000 high-risk pregnancies, carried out for detecting chromosomal abnormalities in Koreans.
Chromosome Aberrations ; Chromosomes, Human, Pair 20* ; Constitution and Bylaws ; Fetus ; Mosaicism ; Placenta ; Pregnancy, High-Risk* ; Trisomy ; Uniparental Disomy*

Patients with Beckwith-Wiedemann syndrome (BWS) are predisposed to developing embryonal tumors, with hepatoblastoma being the most common type. Our patient showed hemihypertrophy, macroglossia, and paternal uniparental disomy in chromosome 11 and was diagnosed with BWS. When the patient was 9 months old, a 2.5×1.5 cm oval hypoechoic exophytic mass was detected in the inferior tip of his right liver. Preoperative imaging identified it as hepatoblastoma; however, histologic, immunohistochemistry, and electron microscopic findings were compatible with adrenal cortical neoplasm with uncertain malignant potential. The origin of the adrenal tissue seemed to be heterotopic. Here, we describe for the first time an adrenal cortical neoplasm with uncertain malignant potential arising in the heterotopic adrenal cortex located in the liver of a patient with BWS.
Adrenal Cortex ; Adrenal Gland Neoplasms ; Beckwith-Wiedemann Syndrome ; Chromosomes, Human, Pair 11 ; Hepatoblastoma ; Humans ; Immunohistochemistry ; Liver ; Macroglossia ; Uniparental Disomy

Neonatal diabetes mellitus (NDM) is defined as hyperglycemia that presents clinical symptoms within the first month of life and requires insulin therapy to maintain euglycemia. The diabetic condition may be transient, permanent, or transient with recurrence later in life. NDM is a rare clinical disorder. Three cases of NDM have been reported in Korea so far. We experienced two cases of NDM in twin brothers who were born with small for gestational ages. Their HLA typings were DR9 and DR14, and insulin autoantibody, islet cell antibody, GAD-reactive autoantibody, and insulin receptor antibody were not found. The genetic analysis with polymorphic DNA markers for chromosome 6 indicated paternal uniparental isodisomy.
Chromosomes, Human, Pair 6 ; Diabetes Mellitus* ; Genetic Markers ; Gestational Age ; Histocompatibility Testing ; Humans ; Hyperglycemia ; Insulin ; Islets of Langerhans ; Korea ; Receptor, Insulin ; Recurrence ; Siblings* ; Twins* ; Uniparental Disomy

BACKGROUND: Megalencephalic leukoencephalopathy with subcortical cysts (MLC) is a rare inherited disorder characterized by infantile-onset macrocephaly, slow neurologic deterioration, and seizures. Mutations in the causative gene, MLC1, are found in approximately 75% of patients and are inherited in an autosomal recessive manner. We analyzed MLC1 mutations in five unrelated Korean patients with MLC. METHODS: Direct Sanger sequencing was used to identify MLC1 mutations. A founder effect of the p.Ala275Asp variant was demonstrated by haplotype analysis using single-nucleotide polymorphic (SNP) markers. Multiple ligation-dependent probe amplification (MLPA) and comparative genomic hybridization plus SNP array were used to detect exonic deletions or uniparental disomy (UPD). RESULTS: The most prevalent pathogenic variant was c.824C>A (p.Ala275Asp) found in 7/10 (70%) alleles. Two pathogenic frameshift variants were found: c.135delC (p.Cys46Alafs*12) and c.337_353delinsG (p.Ile113Glyfs*4). Haplotype analysis suggested that the Korean patients with MLC harbored a founder mutation in p.Ala275Asp. The p.(Ile113Glyfs*4) was identified in a homozygous state, and a family study revealed that only the mother was heterozygous for this variant. Further analysis of MLPA and SNP arrays for this patient demonstrated loss of heterozygosity of chromosome 22 without any deletion, indicating UPD. The maternal origin of both chromosomes 22 was demonstrated by haplotype analysis. CONCLUSIONS: This study is the first to describe the mutational spectrum of Korean patients with MLC, demonstrating a founder effect of the p.Ala275Asp variant. This study also broadens our understanding of the mutational spectrum of MLC1 by demonstrating a homozygous p.(Ile113Glyfs*4) variant resulting from UPD of chromosome 22.
Alleles ; Chromosomes, Human, Pair 22* ; Comparative Genomic Hybridization ; Exons ; Founder Effect ; Haplotypes ; Humans ; Leukoencephalopathies* ; Loss of Heterozygosity ; Megalencephaly ; Mothers ; Seizures ; Uniparental Disomy*