Amino Acid Metabolic Disorders

Nevada Newborn Screening Program

Newborn Screening For Amino Acid Metabolic Disorders

Amino Acid Disorders (AAs) are a group of rare inherited conditions and 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 nonworking 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. People with these kinds of disorders may need to limit or avoid certain foods because their bodies cannot process them properly. Illness or infection, eating the wrong kinds of foods, or going for a long time without eating can bring about signs and symptoms of each disorder. The symptoms and treatment vary between different amino acid disorders. They can also vary from person to person with the same amino acid disorder. See the fact sheets for each specific amino acid disorder.

Amino acid disorders are inherited in an autosomal recessive manner and affect both males and females. This means they are passed from parent to child through genes. Genes are parts of your body's cells that store instructions for the way your body grows and works.

What organic acid metabolism disorders are tested for in newborn screening?

Argininosuccinic Aciduria (ASA)

In ASA, the body cannot remove ammonia or a substance called argininosuccinic acid from the blood. ASA affects one out of every 70,000 babies born in the United States each year. Babies with ASA who do not get treatment often die within the first few weeks of life. Early treatment can help prevent serious problems, including brain damage, liver problems and intellectual and developmental disabilities.

Signs and symptoms of ASA in newborns include:

  • Drowsiness
  • Fussiness
  • Little appetite
  • Throwing up

Signs and symptoms of ASA in older babies and young children can be mild or serious. Physical and behavioral signs and symptoms include:

  • Being restless or having trouble being still or quiet
  • Changes in muscle tone
  • Coordination or balance problems
  • Drowsiness
  • Dry hair that breaks easily
  • Learning problems
  • Slow growth
  • Small head
  • Unclear speech

Medical signs and symptoms of ASA in older babies and children include:

  • Breathing problems
  • High levels of ammonia in the blood can cause intense headache, especially after a high-protein meal
  • Little appetite and disliking meat/high-protein foods
  • Throwing up
Citrullinemia (CIT)

In CIT, the body has trouble breaking down amino acids and getting rid of ammonia in the blood. For babies with CIT, the liver may not work properly to help get rid of ammonia in the body. CIT affects one out of every 57,000 babies born in the United States each year.

The form of CIT called classic CIT usually appears in the first few days after birth. If untreated, a baby with classic CIT can die within the first week of life. Health problems caused by CIT can include brain damage, intellectual and developmental disabilities, liver problems and coma. Milder forms of CIT may not start until childhood or later.

Signs and symptoms of classic CIT in babies include:

  • Breathing problems
  • Changes in muscle tone
  • Drowsiness
  • Fussiness
  • Little appetite or trouble eating
  • Loss of consciousness (passing out)
  • Low body temperature
  • Throwing up
  • Weak muscles

Signs and symptoms of milder forms of CIT in older babies and young children are the same as for those for older babies and children with ASA.

Homocystinuria (HCY)

In HCY, the body cannot break down the amino acid homocysteine. HCY affects one out of every 200,000-300,000 babies born in 100,000 in the United States each year. If untreated, HCY can cause problems with the blood, bones, eyes, heart and pancreas. Babies with HCY may look healthy at birth, but symptoms usually appear within the first year of life.

Physical signs and symptoms include:

  • Being tall and thin with long legs and arms, or long, curved fingers
  • Chest deformities (abnormal shape)
  • Dislocation of the eye lens
  • Failure to thrive (slow weight gain and growth)
  • Knock knees
  • Pale hair and skin
  • Problems with movement
  • Redness across the cheeks

Behavioral signs and symptoms include:

  • Behavior and emotional problems
  • Intellectual and developmental disabilities
Maple Syrup Urine Disease (MSUD)

This disorder gets its name because people with the condition may have urine that smells like maple syrup. In this disorder, the body cannot break down the amino acids leucine, isoleucine and valine. These amino acids are found in foods high in protein, like meat, fish and eggs. Less than one in 100,000 babies is born with MSUD each year in the United States.

If not treated early, babies who are very sick with MSUD often die within the first month of life. Early treatment can help prevent serious health problems, including brain and spinal cord problems, coma and seizures. If treated early, most babies with MSUD can live healthy lives.

Babies with MSUD may seem normal at birth but show signs and symptoms when they start eating protein in food. Signs and symptoms include:

  • Drowsiness
  • Fussiness
  • High levels of acids and ammonia in the blood
  • High-pitched cry
  • Little appetite or trouble feeding
  • Throwing up
  • Urine that smells like maple syrup
  • Weight loss
Phenylketonuria (PKU)

In PKU, the body cannot break down the amino acid phenylalanine. Signs and symptoms of PKU do not appear in the first month of life. At least one in every 10,000-15,000 babies in the United States is born with PKU each year. Different forms of phenylketonuria vary in their severity of signs. Classic phenylketonuria (PKU) is the most severe form. Babies with PKU usually seem healthy at birth. Signs of PKU begin to appear around six months of age.

Signs of classic PKU include:

  • Irritability
  • Seizures (epilepsy)
  • Dry, scaly skin (known as eczema)
  • "Musty" or "mouse-like" body odor
  • Pale hair and skin
  • Developmental delays
Tyrosinemia, Type I (TYR I)

In TYR I, the body cannot break down the amino acid tyrosine. Less than one in 100,000 babies is born with TYR I each year in the United States. If untreated, TYR 1 can cause liver and kidney problems, seizures, rickets, coma and death.

Signs and symptoms include:

  • Breathing problems
  • Bruising or bleeding, especially nosebleeds
  • Diarrhea, bloody stools, throwing up
  • Drowsiness
  • Fast heartbeat
  • Fussiness
  • Jaundice
  • Skin or urine that smells like cabbage
  • Slow weight gain and growth
  • Swollen belly or legs
  • Trouble walking
Tyrosinemia, Type II (TYR II)

TYR II is a condition that can affect the eyes, skin, and intellectual development. It affects less than one in 250,000 individuals. Signs of TYR II usually begin in the first year of life. These signs include:

  • Increased tear production
  • Sensitivity to light (called photophobia)
  • Eye redness
  • Skin lesions on the hands and feet
  • Behavior changes
  • Poor coordination
Argininemia (ARG)

ARG is a condition that causes harmful amounts of arginine and ammonia to build up in the body. ARG affects as many as one in every 300,000 babies born in the United States. Signs of ARG can begin any time from infancy to childhood. Usually, signs begin to show at around one to three years of age. Signs of ARG include:

  • Delayed growth
  • Developmental delays
  • Balancing trouble
  • Tight, rigid muscles (called spasticity)
  • Irritability
  • Poor appetite
  • Sleeping longer or more often
  • Vomiting
  • Weak muscle tone (called hypotonia)
  • Breathing trouble
  • Trouble regulating body temperature
  • Small head size
  • Hyperactivity