According to Janet Thomas, M.D., of the Department of Pediatrics at the University of Colorado School of Medicine, approximately 1 in 1,500 children has a congenital metabolic disease. Called inborn errors of metabolism, just one defective gene can block an entire metabolic pathway. The defect causes some substances to accumulate, while it causes a deficiency of others. The accumulated substances not only affect the organ where the accumulation occurs, but at times, also affect organs at a distance.
Glycogen Storage Diseases
Glucose is used as energy by all of the cells in your body. When not immediately needed, it is stored as glycogen in your liver and muscles. There are several types of glycogen storage diseases. Six types affect glycogen metabolism in your liver. With any of these types, you will have an enlarged liver, problems with growth and severe hypoglycemia (low glucose levels) between meals. Three types of glycogen storage diseases affect your muscles, resulting in muscle weakness. An infant's heart muscle can also be affected.
Galactosemia
In this metabolic disorder, the infant is missing an enzyme (galactose-1-phosphate uridyltransferase) that is needed for one of the steps in changing galactose to glucose. Because that enzyme is missing, a specific substance (galactose-1-phosphate) will accumulate in the liver and kidney. The infant will have vomiting, an enlarged liver and jaundice. The liver will be so damaged that it can lead to cirrhosis. The accumulation of galactose is converted to a substance (galactitol) in the lens of the eye, which will cause the infant to have cataracts.
Phenylketonuria (PKU)
In PKU, there is a deficiency of an enzyme (phenylalanine hydroxylase), which is needed to change the amino acid phenylalanine to the amino acid tyrosine. Without this enzyme, the amino acid phenylalanine accumulates. The infant will have seizures and mental retardation but also fair skin, eczema and a musty body odor. According to Dr. Thomas, every newborn child is now screened for this metabolic disease, so treatment can be initiated to prevent any seizures or mental retardation from occurring .
Maple Syrup Urine Disease
This congenital disease occurs because there is a deficiency of an enzyme needed to metabolize the amino acids isoleucine, leucine and valine. There are many forms of this disease, but the typical form causes seizures, mental retardation and coma. And if the infant is not properly diagnosed and treated, they can die within a month. The disease has its name because the urine smells like maple syrup due to the accumulation of leucine and isoleucine.
Homocystinuria
Homocystinuria is caused by a deficiency of either of two enzymes--CBS or MTHR--or because an enzyme has not been produced. This can cause mental retardation, osteoporosis, a dislocated lens of the eye and blood clots. The child will have high levels of the amino acid homocysteine in the urine.
Hereditary Fructose Intolerance
This inborn error is due to a deficiency of an enzyme (frustose-1-phosphate aldolase) that is needed in one of the steps in the metabolism of fructose. Thus, a substance (fructose-1-phosphate) accumulates. The child will have vomiting, an enlarged liver and jaundice. If untreated, the child will die from liver failure.
References
- "Current Diagnosis & Treatment: Pediatrics"; William Hay, Jr., M.D., Myron Levin, M.D., Judith Sondheimer, M.D., Robin Deterding, M.D.; 2009
- "The Merck Manual: Amino Acid and Organic Acid Metabolism Disorders"
- "The Merck Manual: Carbohydrate Metabolism Disorders"
