Amino Acid Disorder Information


Arizona Network for PKU and Allied Disorders wants to raise awareness for Amino acid disorders (AAs) are a group of rare inherited conditions.

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Amino Acid Disorders


Amino acid disorders (AAs) are a group of rare inherited conditions. They are caused by enzymes that do not work properly.Protein is made up of smaller building blocks called amino acids. A number of different enzymes are needed to process these amino acids for use by the body. Because of missing or non-working enzymes, people with amino acid disorders cannot process certain amino acids. These amino acids, along with other toxic substances, then build up in the body and cause problems.  These diseases can affect many organs and usually affect more than one. Symptoms often tend to be non-specific and usually relate to major organ dysfunction or failure. Which means damage can occur without the person being aware of it. Inherited metabolic disorders vary from degenerative to acute life-threatening. The symptoms and treatment vary between different amino acid disorders. They can also vary from person to person with the same amino acid disorder.

WHY?
Each parent of a child with an autosomal recessive metabolic disorder carries a recessive defective gene along with a normal gene; therefore, both parents are carriers and are not affected by the disorder. Persons with metabolic disorders have received a defective gene from each parent.

When both parents are carriers, there is a 1 in 4 chance with each pregnancy that the baby will receive a defective gene from each parent and have a metabolic disorder; a 2 in 4 chance the baby will be a carrier; and a 1 in 4 chance the baby will receive two normal genes (unable to pass the disorder on to offspring).

Newborn Screening
Although each metabolic disorder included in expanded newborn screening programs is rare, metabolic disorders in general have the potential to affect 1 in 2,400 infants annually. Routine newborn screening in the US began in the 1960’s for a single biochemical genetic disorder, phenylketonuria (PKU). Over the years, other metabolic disorders were added to the routine screenings. In the past, testing for each disorder required a separate test and a separate disk punched from a dried blood sample on filter paper. However, recent application of tandem mass spectrometry provides the opportunity to screen for many disorders with only a single blood sample.

What happens?
PKU occurs when an enzyme, called “phenylalanine hydroxylase” (PAH), is either missing or not working properly. The job of this enzyme is to chemically change the amino acid phenylalanine (Phe – pronounced ‘fee’) into other substances. When a child with PKU eats food containing Phe, it builds up in the blood and causes problems. Phe is found in almost every food, except pure fat and sugar. Babies with PKU seem perfectly normal at birth. The first effects are usually seen around 6 months of age. Untreated infants may be late in learning to sit, crawl and stand. They may pay less attention to things around them. Without treatment, a child with PKU will have mental retardation.
Maple Syrup Urine Disease (MSUD) is an inherited metabolic disorders that affect the way the body metabolizes (processes) certain components of the branched chain amino acids. When these amino acids are not broken down as normally designed, they accumulate in the blood causing a toxic effect that interferes with brain functions. The symptoms of classic MSUD are usually evident within the first week of life and include a poor appetite, irritability, high pitched cry, urine that smells like maple syrup or burnt sugar. Within days, the infants may lose their sucking reflex and grow listless, have a high-pitched cry, and become limp with episodes of rigidity. Without diagnosis and treatment, symptoms progress rapidly to seizures, coma, and death. 

Homocystinuria (HCY) is an inherited disorder in which the body is unable to process certain building blocks of proteins (amino acids) properly. There are multiple forms of homocystinuria, which are distinguished by their signs and symptoms and genetic cause. The most common form of homocystinuria is characterized by nearsightedness (myopia), dislocation of the lens at the front of the eye, an increased risk of abnormal blood clotting, and brittle bones that are prone to fracture (osteoporosis) or other skeletal abnormalities. Some affected individuals also have developmental delay and learning problems.

Citrullinemia (CIT) is one type of amino acid disorder. People with this condition cannot remove ammonia from the body. Ammonia is a harmful substance. It is made when protein and its building blocks, amino acids, are broken down for use by the body. Normally, the body changes ammonia into a substance called “urea”. Urea is then safely removed in the urine. If ammonia is not changed to urea, high levels build up in the blood. This can be very harmful. If ammonia levels stay high for too long, severe brain damage can occur, coma and or death.

Urea Cycle Disorder is a genetic disorder caused by a mutation that results in a deficiency of one of the six enzymes in the urea cycle. These enzymes are responsible for removing ammonia from the blood stream. The urea cycle involves a series of biochemical steps in which nitrogen, a waste product of protein metabolism, is removed from the blood and converted to a compound called urea in the blood. Normally, the urea is transferred into the urine and removed from the body. In urea cycle disorders, the nitrogen accumulates in the form of ammonia, a highly toxic substance, resulting in hyperammonemia (elevated blood ammonia). Ammonia then reaches the brain through the blood, where it can cause irreversible brain damage, coma and/or death.

Treatment
Treatments require daily, life-long dietary monitoring to prevent metabolic crises. Patients with metabolic disorders undergo frequent blood testing to monitor the levels of the amino acids in their blood and/or urine. Illnesses and stress, as well as consuming too much protein, can raise these levels. A metabolic imbalance requires dietary changes, may require medicines, at times, hospitalization. For example: Babies with amino acid disorders may get certain medicines that help help treat the disorder. They may take these medicines by mouth, or they may need to get them through an IV . Treatments are costly and require to maintain a healthy condition .If treatment is started early and continued, babies can develop normally and have normal IQ.

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