MCAD: detected through newborn screening

Genetic screening is defined as the “search in a population for persons possessing certain genotypes that: (1) are already associated with disease or predisposition to disease, or (2) may lead to disease in their descendants” (National Academy of Sciences, 1975). The principles of screening were developed in the 1960's and state that the disease should be relatively common, its natural history understood and there should be an effective treatment available. The screening test itself should be cost effective, valid and reliable. The primary goal of screening is early detection and early intervention in the disease process and this includes newborn screening, which we introduced last month.

South Carolina currently screens for 6 disorders and this month we will focus our discussion on medium-chain acyl-CoA dehydrogenase deficiency (MCAD). MCAD is a recessive condition, meaning that to be affected, the child would have to inherit one defective gene from each parent. MCAD was first described in 1982 and it is estimated that 1 in 10,000 infants is born with this disorder. The gene is located on chromosome 1 and most patients with MCAD are of Northwestern European origin.

Children with MCAD have an inactive enzyme called medium-chain acyl-CoA dehydrogenase. This enzyme is involved in breaking down fat from foods we eat, as well as stored body fat, into energy. Lacking the ability to fully break down fat results in the accumulation of fatty acids and low energy production. The body must use glucose as an alternate energy source. Once the limited glucose reserves are consumed, hypoglycemia or low blood sugar may result.

Clinical episodes often result from fasting or illness with reduced caloric intake. Clinical features may include vomiting, lethargy, irritability, and if untreated, coma or even death can occur. Prompt recognition and treatment with glucose and hydration are required. It is estimated that 25% of patients die after their first episode and the condition is often mistaken for sudden infant death syndrome (SIDS).

MCAD is a treatable disease. A child with MCAD requires evenly spaced meals to avoid fasting for more than 4-6 hours, a reduced fat and high carbohydrate diet, and supportive and aggressive care during periods of illness. With early detection through newborn screening, proper treatment and lifelong surveillance, a child with MCAD can expect to live a very normal, typical life.