Presentation
Inborn errors may present at almost any time in many different ways, but characteristically, they may do so before birth, at birth, or during the first 2–3 days of life, as sudden death, or as deterioration after normal birth and delivery.
During pregnancy
Women carrying a fetus with a long-chain 3-hydroxyacyl- Coenzyme A dehydrogenase deficiency (LCHAD deficiency) are at high risk of developing complications during pregnancy. The most frequent related disorder is haemolysis, elevated liver enzymes, and low platelet count (HELLP) syndrome, but acute fatty liver at pregnancy and persistent hyperemesis are also recognised.1 In most pregnant women, these complications are not related to the inborn error.
At birth
Several disorders present at or soon after birth. Such presentations include early-onset seizures, severe hypotonia, ascites or hydrops fetalis, and dysmorphic syndromes. Panel 1 shows the main metabolic causes of presentations.2–5 Perinatal asphyxia is a common misdiagnosis in babies presenting with neurological abnormalities, especially in those with congenital lactic acidoses and pyridoxine dependency. Some disorders associated with early-onset fits cause seizures in utero, but these disorders are not generally recognised at the time. By contrast, most fetuses with ascites and many with malformations are detected before birth by prenatal ultrasonography. The biochemical basis of more dysmorphic syndromes will probably be elucidated with time.
Sudden death
Sudden death at age 2–3 days is devastating for any family. Non-metabolic disorders causing sudden death at this age include sepsis and congenital heart disease. Defects of fatty-acid oxidation may also be important, especially long-chain disorders, which can lead to respiratory arrest and heart block or arrhythmias.6 In most cases, necropsy reveals an excess of fat droplets in liver or heart tissue but samples for metabolic tests should be obtained as soon as possible after death, without waiting for necropsy (panel 2). Under these circumstances, collection of blood spots on Guthrie cards is especially important for analysis of acylcarnitines and a sample for DNA extraction and skin for fibroblast culture.