Mutation Spectrum and Genotype-Phenotype Correlation in a Cohort of Argentine Patients with Ornithine Transcarbamylase Deficiency: A Single-Center Experience

Abstract X-linked ornithine transcarbamylase deficiency (OTCD) is the most common urea cycle disorder. Hemizygous males with complete deficiency manifest neonatal acute hyperammonemia, while those with partial deficiency have a late presentation. The symptomatology of heterozygotes depends on the inactivation pattern of X chromosome. Hyperammonemic episodes can cause neurological damage and are potentially fatal. Here, we match clinical, biochemical, and molecular findings with bioinformatics analyses to report genotype-phenotype correlations in 14 Argentine patients with OTCD from 11 unrelated families: 4 hemizygotes with neonatal onset (complete OTC gene deletion, 533C > T, c.540+1G > A, c.697delG); 4 hemizygotes with late onset (c.216+1G > A, c.386G > A, c.622G > A, c.829C > T); and 6 symptomatic heterozygotes (complete OTC gene deletion, c.533C > T, c.452T > G, c.540+1G > A, dupE1-9/delE10). Three of these mutations were previously unreported: c.540+1G > A, c.697delG, and dup1-9/del10. Our data highlight the relevance of combining molecular and bioinformatics analyses for accurate diagnosis and outcome prediction in suspected patients with OTCD and the importance of carrier testing for effective genetic counseling.

Preimplantation Genetic Diagnosis for Ornithine Transcarbamylase Deficiency by Simultaneous Analysis of Duplex-nested PCR and Fluorescence In Situ Hybridization: A Case Report

Ornithine transcarbamylase (OTC) deficiency is an X-linked co-dominant disorder. A couple, with a previous history of a neonatal death and a therapeutical termination due to OTC deficiency, was referred to our center for preimplantation genetic diagnosis (PGD). The female partner has a nonsense mutation in the exon 9 of the OTC gene (R320X). We carried out nested polymerase chain reaction (PCR) for R320X mutation and fluorescence in situ hybridization (FISH) for aneuploidy screening. Among a total of 11 embryos, two blastomeres per embryo from 9 embryos were biopsied and analyzed by duplex-nested PCR and FISH, and one blastomere per embryo from 2 embryos by only duplex-nested PCR. As a result of PCR and restriction fragment length polymorphism analysis, four embryos were diagnosed as unaffected embryos having the normal OTC gene. Among these embryos, only one embryo was confirmed as euploidy for chromosome X, Y and 18 by FISH analysis. A single normal embryo was transferred to the mother, yielding an unaffected pregnancy and birth of a healthy boy. Based on our results, PCR for mutation loci and FISH for aneuploidy screening with two blastomeres from an embryo could provide higher accuracy for the selection of genetically and chromosomally normal embryos in the PGD for single gene defects.

A Case of Ornithine Transcarbamylase (OTC) Deficiency

OTC deficiency is an X-linked disorder in which the synthesis of urea is impaired. OTC catalyzes the synthesis of citrulline from carbamyl phosphate and ornithine. Complete or partial deficiencies of this enzyme may lead to Reye syndrome like picture such as encephalopathy, hepatic dysfunction, hyperammonemia, etc. We recently had a case that was presented as recurrent Reye syndrome, and was effectively treated with hemodialysis, arginine, sodium benzoate, etc. This report describes an experience in treating this condition with review of available literature.

Characterization of Molecular Defects in Korean Families with Inherited Ornithine Transcarbamylase Deficiency and Their Genotype-Phenotype Correlations

PURPOSE: This study was undertaken to characterize molecular defects in Korean families with ornithine transcarbamylase(OTC) deficiency, correlate it with phenotype using in vitro expression study, and utilize it for making prenatal molecular diagnosis. METHODS: To investigate molecular lesions resulting in OTC deficiency in 15 unrelated Korean families, the OTC genes of probands were amplified exon by exon and analyzed by direct sequencing of double stranded DNA. Based on their molecular lesions, prenatal monitoring of six fetuses at risk from four unrelated families was performed using genomic DNA from chorionic villi sampling(CVS). To analyze expression in vitro, mutant OTC cDNAs were constructed and cotransfected with beta-galactosidase gene into COS-1 cells by using lipofection. After transient expression, OTC activity was measured by colorimetric method. RESULTS: Nine different mutations were identified in 10 out of 15 families ; six mutations were novel, involving well-conserved nucleotide sequences across species or CpG hot spot : T44I, M205T, H214Y, D249G, F281S, R320X. In vitro expression study revealed that the H214Y mutant showed a residual enzyme activity(13% vs 0% for D249G, 0% for R320X). However, clinical phenotype for H214Y was severe with neonatal onset. Three mutations were previously reported in other ethnic groups : R26Q, R141Q, R277W. Prenatal evaluation of 6 fetuses including one fraternal twins were successfully made. We predicted the outcome of all fetuses prenatally. They were also tested postnatally for the mutations to be unaffected. CONCLUSION: The genotypes of Korean patients with OTC deficiency are genetically heterogeneous. Therefore, molecular diagnosis should be individualized in each family with OTC deficiency.