NeurometPlus

Incidence

Theoretically, the prevalence of maternal PKU syndrome should be the same as the prevalence of phenylalanine hydroxylase (PAH) deficiencies itself, i.e. 1/15000 live births on the average (considering the mean reproductive rate per couple to be 2, and since 1 PKU patient out of 2 is female). Fortunately, the actual prevalence is lower than that, since untreated PKU women are mentally retarded and consequently have no or few offspring, and since the majority of treated PKU women are nowadays informed and carefully managed during their pregnancies.

Clinical Characteristics

Maternal phenylketonuria (PKU) during pregnancy leads to a risk of spontaneous abortion or embryopathy. The severity of embryopathies depends on the level of maternal phenylalaninemia and may associate malformations including cardiopathy (usually conotruncal), corpus callosus agenesis, neuronal migration disorders, facial dysmorphism and more rarely cleft palate, tracheo-esophageal abnormalities..., but especially fetal development disorders, including microcephaly, intrauterine growth retardation, and subsequent mental retardation. This embryopathy can be prevented by a strict low-phenylalanine diet started before conception and maintained throughout pregnancy. Girls with phenylalanine hydroxylase (PAH) deficiency must be fully informed, so as in to program pregnancies, when the time comes, and control the phenylalanine level before conception. Maternal PKU may be suggested in fetuses or children whose mothers were born before the systematic screening of newborns for PKU or in a country were there is no screening at all. The gravity of maternal PKU syndrome is reflected by the maternal plasma concentration; over 20 mg/dL, the risk is major. In 1980, Lenke and Levy published the first exhaustive description of the syndrome, in untreated women. For a plasma concentration over 20 mg/dL during pregnancy, the frequency of the following feature was the following: Mental retardation 92%, Microcephaly 73%, Congenital heart disease 12%, Birth weight < 2500 g 40%. The exact frequencies of the other features are less precise: facial dysmorphism (frequent), corpus callosus agenesis (frequent), tracheo-esophageal malformations and cleft palate (rare, 1-5%).

Precipitants

None

Provocation Tests

None

Diagnostic Procedures

For women whose phenylketonuria (PKU) was known before pregnancy, the diagnosis of maternal PKU syndrome is based on the ultrasound recordings measuring fetal growth parameters, the examination of the neonate with measurement of birth and growth parameters, searching for compatible malformations, and the follow-up of the child regarding his head circumference growth and cognitive milestones. For women not known to have PKU, the diagnosis can be made only if the physician is highly sensitized to such a possibility and indeed thinks of it, measuring the mother's plasma phenylalanine level.