What Is Short-Chain Acyl-CoA Dehydrogenase Deficiency?
Short-Chain acyl-CoA dehydrogenase (SCAD) deficiency is an inherited disease caused by mutations in the ACADS gene and part of a group of disorders called fatty-acid oxidation defects. Individuals with SCAD deficiency can have trouble converting short-chain fatty acids for energy to fuel their body. Symptoms may be triggered by long periods without food (fasting), by illness, or by other stressors.
Some infants with SCAD deficiency experience episodes of metabolic crisis that can involve vomiting, low blood sugar, and fatigue. These metabolic crises can be life-threatening. Affected infants may also have difficulty feeding and failure to grow at the expected rate. Some other symptoms may include poor muscle tone, seizures, smaller head size (microcephaly), an enlarged liver, and an enlarged spleen. Untreated SCAD deficiency can lead to developmental delay and learning problems.
Some individuals with SCAD deficiency do not display any symptoms until adulthood. In these cases, the main symptom is chronic muscle weakness while some may experience periods of pain, nausea, and shortness of breath. Due to the wide variability of the disease, it is possible for individuals not to have any symptoms or to have symptoms so mild that they are never diagnosed.
How Common Is Short-Chain Acyl-CoA Dehydrogenase Deficiency?
SCAD deficiency affects 1 in 40,000 to 1 in 100,000 newborns. Researchers have hypothesized that this disease may be more common than believed because some individuals with the disease are asymptomatic or have mild symptoms.
How Is Short-Chain Acyl-CoA Dehydrogenase Deficiency Treated?
The key to managing SCAD deficiency is to avoid going for long periods of time without eating. Infants and children with SCAD deficiency may require feedings at regular intervals, including during nighttime. For children and adults, consuming cornstarch can also provide a sustained release of energy and allow for longer gaps between meals. If an individual is unable to eat or drink food on their own, it may be necessary to give them glucose by intravenous fluids. Some physicians may recommend carnitine or riboflavin supplements as well.
What Is the Prognosis for an Individual with Short-Chain Acyl-CoA Dehydrogenase Deficiency?
Early diagnosis and dietary management are important for the best outcome. If dietary management starts early and is consistent, individuals with SCAD deficiency have a good prognosis with normal or near-normal lifespan. Some individuals with SCAD deficiency may not experience symptoms until adulthood or may only experience very mild symptoms until adulthood.
Additional Considerations for Carriers
Carriers of fatty-acid oxidation defects, including SCAD deficiency, do not typically show symptoms of the disease. However, there is an increased risk of serious pregnancy complications, particularly in the third trimester, in women carrying a fetus affected with SCAD deficiency. These complications can include HELLP syndrome and acute fatty liver of pregnancy. A woman whose pregnancy may be affected by a fatty-acid oxidation defect, such as SCAD deficiency, should speak with her physician for recommendations and may benefit from consultation with a high-risk physician.