Effects of oral contraceptives and obesity on carrier tests for phenylketonuria

Brown, E. Sherwood; Waisman, Harry A.; Swanson, Marilyn A.; Colwell, Robert E.; Banks, Mary Ellen; Gerritsen, Theo

doi:10.1016/0009-8981(73)90380-x

Cited by 13 publications

(3 citation statements)

References 17 publications

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“…One possible explanation is the effect of oestrogen and progesterone levels on phenylalanine and tyrosine concentrations in heterozygote females. This has been reported previously (Jackson et al 1971;Brown et al 1973;Griffin et al 1973) and is supported by our findings of the higher plasma phenylalanine/tyrosine molar ratio in both controls (p < 0.05 by the t method) and heterozygote females (p < 0.10 by the t method) taking the contraceptive pill.…”

Section: Discussionsupporting

confidence: 92%

Plasma phenylalanine and tyrosine levels revisited in heterozygotes for hyperphenylalaninaemia

Saraiva¹,

Seakins²,

Smith³

1992

J of Inher Metab Disea

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We examined the value of the fasting plasma phenylalanine/tyrosine ratio obtained in an ordinary clinical setting for assessing the probability of being a heterozygote for hyperphenylalaninaemia. This biochemical test was found to be of little value in those with a high (66%) prior risk of heterozygosity, because it could not reduce the risk below 12%. However, in a population with a prior risk of only 2%, it discriminates the 3% with a 19% risk from the 97% with a risk of 1.5% or less. This simple method could usefully be applied to such a population, in order to select those at higher risk for further investigation using molecular genetics.

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Section: Discussionsupporting

confidence: 92%

Plasma phenylalanine and tyrosine levels revisited in heterozygotes for hyperphenylalaninaemia

Saraiva¹,

Seakins²,

Smith³

1992

J of Inher Metab Disea

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“…Since our samples were collected from all over the country, it was judged impossible to standardize the sampling procedure in any other way than by using fasting morning samples. Potential effects on PHE or TYR of body weight, pregnancy and oral contraceptives (Brown et al 1973;Scriver et al 1989), age (Armstrong and Stave 1973b), drugs, and diseases or deficiencies such as iron deficiency (references in Hilton et al 1986) may have contributed to the error rate. The effect of sex on PHE that we observed and corrected for is in agreement with the findings of Armstrong and Stave (1973a) but in contrast to those of Scriver et al (1985) and Hilton et al (1986), who did not find any significant sex-related effect.…”

Section: Discussionmentioning

confidence: 99%

Severity of mutation in the phenylalanine hydroxylase gene influences phenylalanine metabolism in phenylketonuria and hyperphenylalaninaemia heterozygotes

Svensson¹,

Iselius

Hagenfeldt³

1993

J of Inher Metab Disea

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We examined whether the degree of residual activity from the mutant phenylalanine hydroxylase (PAH) allele affected phenylalanine metabolism in heterozygotes for phenylketonuria (PKU) or non-PKU hyperphenylalaninaemia (HPA). Discriminant analysis was carried out to find the function of fasting plasma concentrations of phenylalanine (PHE) and tyrosine (TYR) that best separated carriers from non-carriers. This function (0.103TYR -0.214-PHECORR -4.499) was subsequently used as the dependent variable, with the in vitro activity of the expressed mutant PAH as the independent variable, in a regression analysis performed on heterozygotes for mutations that had been studied in a eukaryotic cell expression system. This analysis showed a significant correlation (r = 0.40, n = 140, p < 0.001), although there was a wide spread of values within each of the two major groups of carriers and a considerable overlap between the groups. We conclude that the severity of the mutation, as determined by in vitro expression analysis, in the mutant PAH gene is reflected in the biochemical phenotype of heterozygotes. This result emphasizes the relevance of the cell expression system used for establishing the relative severities of most mutations at the PAH locus. Differences in the activities from the carried mutant PAH allele on phenylalanine metabolism in heterozygotes are, however, small compared to the activity from the normal PAH allele and are easily obscured by other factors leading to inter- or intra-individual variation in phenylalanine metabolism. Fasting plasma concentrations of phenylalanine and tyrosine thus can not be used to predict the severity of the carried PAH mutation in individual PKU or HPA heterozygotes.

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“…None of the adults was obese and females were tested on days when they were not taking oral contraceptives [2]. None of the adults was obese and females were tested on days when they were not taking oral contraceptives [2].…”

Section: A T E R I a L A N D M E T H O D Smentioning

confidence: 99%

Serum tyrosine within the first hour after an oral load of phenylalanine

Güttler

Hansen

1977

Scandinavian Journal of Clinical and Laboratory Investigation

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Twenty-seven heterozygotes for phenylketonuria (PKU) and sixteen normal homozygotes were loaded with an amount of L-phenylalanine per body mass = 0.6 mmol/kg. Serum tyrosine concentration increased significantly within 15 min after the intake and the increase was rectilinear within the first 30 min. The initial rate of increase in serum tyrosine in heterozygotes was 0.47 mumol/l/min (range 0.20-0.98 mumol/l/min) and in normal homozygotes 1.2 mumol/l/min (range 0.80-1.9 mumol/l/min). The median serum tyrosine concentration increased within the first hour after an oral phenylalanine load (0.6 mmol/kg) of twelve infants with persistent hyperphenylalaninaemia (HPA), whereas serum tyrosine showed a decrease in forty infants with classical PKU. In ninetten infants with mild PKU serum tyrosine remained unchanged within the first hour after the load and then declined.

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Effects of oral contraceptives and obesity on carrier tests for phenylketonuria

Cited by 13 publications

References 17 publications

Plasma phenylalanine and tyrosine levels revisited in heterozygotes for hyperphenylalaninaemia

Plasma phenylalanine and tyrosine levels revisited in heterozygotes for hyperphenylalaninaemia

Severity of mutation in the phenylalanine hydroxylase gene influences phenylalanine metabolism in phenylketonuria and hyperphenylalaninaemia heterozygotes

Serum tyrosine within the first hour after an oral load of phenylalanine

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