The objective of this review is to draw attention to those inherited metabolic traits which are potentially harmful also for the carrier, and to outline preventive measures, at least for obligate heterozygotes, i.e. parents of homozygous children. Concerning carriers of food-dependent abnormalities, early
vascular disease in
homocystinuria, hyperammonaemic episodes in
ornithine transcarbamylase deficiency, presenile
cataracts in galactosaemia as well as
galactokinase deficiency,
spastic paraparesis in
X-linked adrenoleukodystrophy, and
HELLP syndrome in mothers of babies with
long-chain 3-hydroxyacyl-coenzyme A dehydrogenase deficiency have to be mentioned. In the group of food-independent disorders, clinical features in carriers may be paraesthesias and
corneal dystrophy in
Fabry disease, lens clouding in
Lowe syndrome, lung and/or
liver diseases in
alpha 1-antitrypsin deficiency, and renal stones in
cystinuria type II and III. Finally, two monogenic carrier states are known which in pregnant individuals could possibly afflict the developing fetus, i.e. heterozygosity for galactosaemia and for
phenylketonuria. Elevated levels of
galactose-1-phosphate have been found in red blood cells of infants heterozygous for galactosaemia born to heterozygous mothers.
Aspartame in very high doses is reported to increase blood
phenylalanine levels in heterozygotes for
phenylketonuria, thus being a risk for the fetus of a heterozygous mother. For some of these carrier states preventive measures can be recommended, e.g. restriction of
lactose in parents and heterozygous grandparents of children with galactosaemia and
galactokinase deficiency as well as transiently in infants heterozygous for galactosaemia, dietary supplementation with
monounsaturated fatty acids in symptomatic carriers for
X-linked adrenoleukodystrophy, avoidance of smoking and alcohol in heterozygotes for
alpha 1-antitrypsin deficiency, avoidance of episodes of
dehydration in heterozygotes for
cystinuria, and restriction of
aspartame in pregnant women.