Maternal phenylketonuria: a metabolic teratogen

Transport of large neutral amino acids into BeWo cells

BeWo choriocarcinoma cells were cultured onto solid microcarrier beads, packed into columns and superfused. Unidirectional influx of l -phenylalanine (l -phe) and l -leucine (l -leu) across the microvillous border of the cells was studied using a rapid paired-tracer dilution technique. Influx of l -phe and l -leu comprised both saturable and non-saturable components. K(m)values for l -phe and l -leu were 0.57+/-0.01 m m and 0.05+/-0.01 m m, respectively, with V(max)values of 120.4+/-0.5 nmol/mg/min and 41. 7+/-0.2 nmol/mg/min. Non-saturable uptake components were 29.0+/-0.1 nmol/mg/m m and 37.9+/-0.1 nmol/mg/min/m m respectively. l -leu uptake was found to be sodium-independent. The uptake of l -[(3)H]phe was strongly inhibited (90-100 per cent) by unlabelled l -phe, d -phe, l -leu or 2-aminoendobicyclo-[2,2, 1]-heptane-2-carboxylic acid (BCH) but not by l -arginine (l -arg) or methyl alpha-aminoisobutric acid (Me-AIB). Pre-incubation of Bewo cultures for 24 h in the presence of an additional 1.2 m ml -phe (simulating maternal phenylketonuria) significantly reduced both the K(m)and V(max)components of l -phe influx. l -arg (2 m m) had no effect on l -leu influx whereas 2 m ml -phe completely inhibited saturable l -leu influx. These data suggest that the microvillous border of differentiated BeWo cells transport large neutral amino acids predominantly via system L rather than by B(0) or y(+)L transporters.

[Importance of the diagnoses and treatment of phenylketonuria]

Phenylketonuria is the most common inborn error of amino acid metabolism. It is due to a deficiency of phenylalanine hydroxylase, which normally converts phenylalanine to tyrosine. A diet low in phenylalanine starting in the first month of life can significantly reduce mental retardation, the most important feature of the disease. The aim of the review is to discuss the difficulties found in the diagnosis of PKU and its variants, ranging from classic phenylketonuria to mild hyperphenylalaninaemia, and the effects of dietary restriction of phenylalanine on the growth and development of children. Also, we present the current controversies about the age of discontinuing the dietary treatment. This review summarizes the benefits and problems emerging from a prolonged therapy taking into account dietary compliance in different age groups, and discusses dietary alternatives to the synthetic amino acid mixtures free of phenylalanine, based on low phenylalanine protein hydrolysates. In addition, we show some information about the effects of maternal phenylketonuria on pregnancy outcome and infant development, if exposed to high phenylalanine levels intra uterineo.

Imprinting, the X-chromosome, and the male brain: explaining sex differences in the liability to autism

Males are at least four times more likely to develop autism than females. Among relatives with a broader autistic phenotype, males predominate too. Autism is a highly heritable disorder, yet genome scans have not revealed any predisposing loci on the sex chromosomes. A nongenetic explanation for male vulnerability, such as exposure to prenatal androgens, is unlikely for a variety of reasons. A novel genetic mechanism that resolves many of the outstanding difficulties is outlined here. The imprinted-X liability threshold model hypothesizes that the threshold for phenotypic expression of many autistic characteristics is influenced by an imprinted X-linked gene(s) that is protective in nature. Imprinted genes are known to play an important role in normal fetal and behavioral development. The gene is expressed only on the X-chromosome that is inherited from the father and raises the threshold for phenotypic expression. It is normally silenced when transmitted maternally. Because only females have a paternal X-chromosome, the threshold for phenotypic expression is higher in them than in males. Evidence for the existence of the genetic locus was found in a study of females with X-monosomy (Turner's syndrome) in which females had either a single paternal or maternal X-chromosome. Identifying the sites of action of this X-linked gene could lead to the discovery of autosomal loci that confer more directly a predisposition to autism.

The Resource Mothers Program for Maternal Phenylketonuria

OBJECTIVES

The purpose of this study was to measure the effectiveness of resource mothers in reducing adverse consequences of maternal phenylketonuria.

METHODS

Nineteen pregnancies in the resource mothers group were compared with 64 pregnancies in phenylketonuric women without resource mothers. Weeks to metabolic control and offspring outcome were measured.

RESULTS

Mean number of weeks to metabolic control was 8.5 (SE = 2.2) in the resource mothers group, as compared with 16.1 (SE = 1.7) in the comparison group. Infants of women in the resource mothers group had larger birth head circumferences and higher developmental quotients.

CONCLUSIONS

The resource mothers program described here improves metabolic control in pregnant women with phenylketonuria.