Prenatal diagnosis of ornithine transcarbamylase deficiency with use of DNA polymorphisms

Apparent segregation of null alleles ascribed to deletions of the ornithine transcarbamylase gene in congenital hyperammonaemia

Ornithine transcarbamylase (OTC) deficiency is an X-linked disorder of the urea cycle mapped to chromosome Xp21.1. Here, we show that apparent segregation of null alleles at the OTC locus and flanking polymorphic loci mimicked false maternity or false paternity in three affected families. Based on these observations, we suggest giving consideration to gene deletion when dealing with segregation of null alleles in OTC deficiency.

Hyperammonemic coma due to parenteral nutrition in a woman with heterozygous ornithine transcarbamylase deficiency

Ornithine transcarbamylase deficiency is an X-linked disorder of the urea cycle that can cause hyperammonemic encephalopathy in hemizygous males and heterozygous females. Affected females typically limit protein intake in their diet. This case report describes a 36-year-old woman with ulcerative colitis who went into hyperammonemic coma after administration of total parenteral nutrition. A similar episode of coma had occurred 7 years earlier after she delivered a normal boy. Heterozygous ornithine transcarbamylase deficiency was diagnosed based on a positive allopurinol tolerance test result after elevated levels of plasma glutamine and low plasma citrulline were detected. The protein load associated with parenteral alimentation resulted in symptomatic expression of this partial enzyme deficiency in this unique case. Partial ornithine transcarbamylase deficiency must always be considered in adult women and men with hyperammonemia who have normal liver function test results.

Use of denaturing gradient gel electrophoresis for detection of mutation and prospective diagnosis in late onset ornithine transcarbamylase deficiency

Ornithine transcarbamylase (ornithine carbamoyltransferase, EC 2.1.3.3) deficiency is an X-linked inborn error of metabolism with considerable phenotypic variability in affected males. Using a combination of the polymerase chain reaction and denaturing gradient gel electrophoresis (DGGE), we defined a mutation in a family in whom affected males have significant residual enzyme activity. A C----T change in the first nucleotide of codon 277 resulted in the substitution of a tryptophan for an arginine at amino acid 245 of the mature protein. This change appears to represent a deleterious mutation rather than a polymorphism on the basis of several factors: the change occurs at a highly conserved arginine residue, significant size and change differences exist between arginine and tryptophan, and this change was not seen on DGGE screening of 26 unrelated individuals representing 43 chromosomes. Diagnosis of an at-risk male newborn in this family was performed using direct mutational analysis. In families with partial enzyme deficiencies in whom biochemical data may be difficult to evaluate, direct detection of mutations at the OTC locus permits definitive diagnosis. This represents the first description of a mutation in late onset OTC deficiency and demonstrates direct mutational analysis by DGGE for prospective diagnosis in a genetic disorder.

Carrier detection in a partially dominant X-linked disease: ornithine transcarbamylase deficiency

Ornithine transcarbamylase (OTC) deficiency is an X-linked disease responsible for lethal neonatal hyperammonemia in males. Partial OTC deficiency also occurs in females and can be responsible for life-threatening hyperammonemic comas in heterozygotes (15%). Increased orotic acid excretion occurs in both symptomatic and asymptomatic carriers, especially under protein loading tests. The disease is therefore partially dominant with neonatal lethality in the hemizygous male; the fraction of new mutations has previously been estimated to be low in males (point estimation = 0, upper bound of the confidence interval = 0.16) and 57% in females. Genetic counseling in this disease is difficult because it is not clear whether a negative protein loading test rules out carrier status. In an attempt to determine how reliable the test is for carrier detection, we investigated ten obligate carriers for orotic acid excretion; considering all data available, we concluded that the test is rarely negative in obligate carriers (8%). Consequently, a negative test in a mother decreases the minimum risk of being a carrier from 84% a priori to 30% if she had an affected son and from 43% a priori to 5% if she had a heterozygous daughter. Finally, the diagnosis of a new mutation in the germ cells of the maternal grandfather in one particular family could be ascertained by extensive DNA analysis.

Structure of the ornithine transcarbamylase (OTC) gene and DNA diagnosis of OTC deficiency

Complementary and genomic DNA clones corresponding to human ornithine transcarbamylase (OTC) have been isolated and analyzed. Restriction fragment length polymorphisms (RFCPs) on OTC gene locus were analyzed in Japanese female population. Based on these data, a prenatal diagnosis of OTC deficiency was carried out in a risk family. A C-to-T substitution was found in exon 5 of OTC gene is an another female patient.

Prenatal diagnosis and heterozygote detection by DNA analysis in ornithine transcarbamylase deficiency

This report summarizes our experience with DNA analysis using a complementary DNA probe for ornithine transcarbamylase in 24 individuals or families with deficiency of this enzyme. In four cases, including three reported elsewhere, a Taql restriction site alteration directly detected the mutation. In 10 additional cases, only an affected male was available, and results of DNA analysis using the Taql enzyme were normal. In 10 cases, family studies were performed with the use of restriction fragment length polymorphisms. Prenatal diagnostic studies were performed for three informative pregnancies, and two affected male fetuses were identified. Analysis of two restriction fragment length polymorphisms, Mspla and BamHl, was informative in 14 of 19 (74%) known carrier females and in 21 of 35 (60%) females (the total number studied). One female previously predicted to be a noncarrier by protein-loading test was determined to be a carrier by analysis of restriction fragment length polymorphisms. The frequency of Taql site alterations was 4 of 24 families (17%). These data illustrate the importance of DNA analysis, pedigree analysis, and biochemical testing in families with ornithine transcarbamylase deficiency to detect carriers and establish the diagnosis prenatally.

Fetal liver alanine: glyoxylate aminotransferase and the prenatal diagnosis of primary hyperoxaluria type 1

Primary hyperoxaluria type 1 (PH1) is caused by a deficiency of the hepatic peroxisomal enzyme alanine: glyoxylate aminotransferase (AGT, EC 2.6.1.44) (Danpure and Jennings, FEBS Lett., 201, 20-24, 1986). The activity of AGT has been measured in fetal livers of gestational age 14-21 weeks. Activity increases up to 17 weeks and then levels off between 17 and 21 weeks. At this time, the mean AGT activity is about 30 per cent of the mean normal postnatal level. As in adult liver, the AGT enzyme activity and the AGT immunoreactive protein are peroxisomal. Prenatal diagnosis has been performed by measuring AGT enzyme activity and immunoreactive AGT protein on liver biopsies from two fetuses at risk for primary hyperoxaluria type 1. One was unaffected and one was affected.

Diagnosis of genetic disorders at the DNA level

In the past 10 years considerable progress has been made in the diagnosis of hereditary disorders at the DNA level. Many monogenic disorders can now be examined at the gene level; such examination has led to a better understanding of the molecular basis of these disorders and made carrier detection and prenatal diagnosis possible. Each year, more and more monogenic disorders can be added to the list of diseases that can be diagnosed by DNA analysis. Future research will be devoted to the identification of genes responsible for other known monogenic hereditary disorders, the elucidation of the molecular lesion associated with chromosomal abnormalities, and the characterization of the genes and gene defects involved in the common multifactorial diseases. The goal of diagnosis is the identification of the genetic defect in affected patients, persons destined to be affected, and carriers.

Characterization of point mutations in the same arginine codon in three unrelated patients with ornithine transcarbamylase deficiency

Point mutations in the X-linked ornithine transcarbamylase (OTC) gene have been detected at the same Taq I restriction site in 3 of 24 unrelated probands with OTC deficiency. A de novo mutation could be traced in all three families to an individual in a prior generation, confirming independent recurrence. The DNA sequence in the region of the altered Taq I site was determined in the three probands. In two unrelated male probands with neonatal onset of severe OTC deficiency, a guanine (G) to adenine (A) mutation on the sense strand (antisense cytosine [C] to thymine [T]) was found, resulting in glutamine for arginine at amino acid 109 of the mature polypeptide. In the third case, where the proband was a symptomatic female, C to T (sense strand) transition converted residue 109 to a premature stop. These results support the observation that Taq I restriction sites, which contain an internal CG, are particularly susceptible to C to T transition mutation due to deamination of a methylated C in either the sense or antisense strand. The OTC gene seems especially sensitive to C to T transition mutation at arginine codon 109 because either a nonsense mutation or an extremely deleterious missense mutation will result.

Xp21 DNA microdeletion in a patient with chronic granulomatous disease, retinitis pigmentosa, and McLeod phenotype

The clinical, biochemical, and molecular analysis of a patient with chronic granulomatous disease (CGD), retinitis pigmentosa (RP), and McLeod phenotype and of his parents demonstrated the X-linked transmission of these three traits in this family and a deletion of the entire X-CGD gene of the patient DNA. All but one other DNA markers tested, including those in Xp21, were present. These findings strongly suggest that the McLeod locus and at least one XL RP gene are closely linked to the X-CGD locus in the Xp21 region of the human X chromosome.

DNA analysis of ornithine transcarbamylase deficiency

By analysing the restriction fragment length polymorphism (RFLP) detected by an ornithinetranscarbamylase (OTC) gene specific DNA probe, we followed the segregation of the defective gene in two families with OTC deficiency (X-linked disease). We were able to exclude some female family members as carriers. In one case a doubtful result obtained in a biochemical carrier detection test (by examining the renal orotic acid excretion after a protein load) could be clarified by DNA analysis. In every family with OTC deficiency, carrier detection should be biochemical with additional DNA analysis. Previous results of the biochemical carrier test should be controlled by DNA analysis, especially when "normal" results were obtained.

Diagnosis of genetic disease using recombinant DNA. Supplement

Recombinant DNA methodology has greatly increased our knowledge of the molecular pathology of the human genome at the same time as providing the means to diagnose inherited disease as the DNA level. We present here a list of recent reports of both direct and indirect analysis of human inherited disease which is intended to serve as a guide to current molecular genetic approaches to diagnostic medicine.

[Recent advances in inborn errors of metabolism]

Four aspects of advances in inborn errors of metabolism (IEM) are analysed: 1) concerning the general comprehension of the pathogenesis, genic localization and genetic heterogeneity; 2) clinical aspects, with description of new variants of known IEM or new IEM; 3) laboratory diagnostic tests presently used in our country: dosage of some genetic markers (arylsulfatases, hexosaminidases, beta-glycosidase; beta-galactosidase and sphingomyelinase), newborn populational screening (for hyperphenylalaninemia, and hypothyroidism), heterozygote detection (for Tay-Sachs disease) and also some prenatal diagnosis; 4) therapeutic aspects presenting substitutive treatment, special diets, plasmapheresis and leukapheresis. The first results of 4 cases of mucopolysaccharidosis treated with the last technic are presented.