Disorders

Phenylketonuria (PKU)

Phenylketonuria (PKU) is a treatable disorder that affects the way the body processes protein. Individuals with PKU cannot process a part of protein called phenylalanine, which is present in most foods. Because of a genetic abnormality, affected individuals lack or have very low levels of an enzyme (phenylalanine hydroxylase or PAH) that converts phenylalanine to other substances the body needs. Without treatment, phenylalanine builds up in the bloodstream and causes brain damage and mental retardation. However, these results can be avoided if dietary treatment is started in early infancy. The dietary treatment, which is required for life, involves severe natural protein restriction and consumption of 'medical food' that is phenylalanine free-but provides all other amino acids.

Maple Syrup Urine Disease (MSUD)

Maple syrup urine disease (MSUD) is a treatable disorder that affects the way the body processes protein. It is caused by a deficiency of an enzyme that breaks down leucine, isoleucine, and valine, which are branched-chain amino acids. If untreated, toxic by-products of these amino acids build up in the blood and urine, which can cause brain damage and even death. MSUD is treated with a special diet that is low in branched-chain amino acids. Since protein is essential for normal growth and development, a special formula that provides protein and essential nutrients, but contains little or no branched-chain amino acids, is required throughout life. To prevent mental retardation, treatment must begin shortly after birth.

Homocystinuria (HCU)

Homocystinuria (HCU) is an inherited disorder in which the body is unable to process the amino acid methionine properly, causing it to accumulate in the blood. Homocysteine, another amino acid that is made from methionine, also accumulates in the blood, which is damaging to the brain and body. The most common form of the condition is caused by the lack of an enzyme called cystathionine beta-synthase. This form of HCU is characterized by dislocation of the lens in the eye, an increased risk of abnormal blood clots, and skeletal abnormalities. Problems with development and learning are also evident in some cases. There is no specific cure for HCU. However, slightly less than half of patients respond to high doses of vitamin B-6 as a treatment. Those who do no respond to vitamin B-6 require a low methionine diet along with a special medical food that provides other amino acids, vitamins, and minerals. Most will also need treatment with trimethylglycine (a medication also known as Betaine). A normal dose of folic acid supplement and occasionally added cysteine (an amino acid) may also be needed.

Tyrosinemia Type 1 (TYR)

Tyrosinemia (TYR) is a genetic disorder characterized by elevated blood levels of the amino acid tyrosine, a building block of most proteins. TYR is caused by the shortage of one of the enzymes required to break down tyrosine. If untreated, tyrosine and its by-products build up in tissues and organs, which leads to serious medical problems.

There are three types of TYR, each caused by the deficiency of a different enzyme. TYR Type I is the most severe form of this disorder, and can lead to liver and kidney failure, problems affecting the nervous system, and an increased risk of liver cancer if untreated. Early diagnosis and prompt treatment is essential for an improved prognosis. Individuals with TYR need to be on a special diet and medications throughout life. Treatment of TYR type I includes a diet restricted in the amino acids tyrosine and phenylalanine, along with a special medical food that provides other amino acids, vitamins, and minerals. Treatment with Nitisinone has been successful and has improved the outcome in TYR type I. If liver disease is already advanced before initiation of treatment, liver transplantation may be necessary.

Organic Acidemias (OAs)

Organic Acidemias (OAs) are a group of metabolic disorders in which enzymes that are required to process certain amino acids are absent or not working properly. Amino acids are the building blocks of protein and are therefore found in any food containing protein. When people with OA eat too much natural protein, the enzyme defect causes a build-up of chemicals, called organic acids, in the blood and urine which damages the brain and other organs. Characteristics of the conditions include general malaise, reluctance to feed, breathing problems, vomiting, hypotonia (floppiness) and/or spasticity (stiffness). There are several different OAs, including but not limited to Propionic Acidemia, Methylmalonic Acidemia, Isovaleric Acidemia, and Glutaric Acidemia.

Since each OA has a slightly different mechanism, symptoms and treatments may vary significantly from disorder to disorder and even between two people with the same disorder. For example, people with Propionic Acidemia and Methylmalonic Acidemia cannot process the amino acids Isoleucine, Valine, Methionine, and Threonine, while those with Isovaleric Acidemia cannot process Leucine. The attributes of treatment that are common to many OAs are; restriction of the amino acid(s) that cannot be processed, consumption of a medical food to provide adequate nutrients for growth and development, and use of compounds to dispose of toxic metabolites and/or increase activity of deficient enzymes. The effect of the disorder will depend upon the age at which symptoms occur. Children with less severe forms of the conditions develop symptoms later. Early detection and treatment can greatly mitigate the effects of the disorder.