Amino Acids (AA) Disorders in Newborns



  • Amino acid disorders incidence excluding Phenylketonuria (PKU) in West Midland (1 in 5354) according to the study conducted in year (2006)

(Sanderson et al, 2006)

  • In British Columbia Amino acid disorder in Newborns is 24 in 100,000 births and 1/ 4,200 (Applegarth et al, January 2000)


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.

Because these disorders produce symptoms early in life, newborns are routinely screened for common ones.


Amino acid metabolic disorders are caused by the body’s inability to breakdown certain amino acids in proteins, or by the inability to detoxify the by-product of amino acids (ammonia) through the urea cycle.  The buildup of amino acids and/or by-products of amino acid metabolism in the blood cause severe medical complications.  If you have one of these disorders, your body may have trouble breaking down certain amino acids. Or there may be a problem getting the amino acids into your cells. Newborns identified to be at risk for an amino acid disorder are referred to a contracted medical center for diagnostic evaluation.

These disorders are inherited (passed from parent to child) conditions. Everyone inherit two copies of the genes that cause amino acid disorders. We receive one copy of each gene one from our father and one copy from our mother. Sometime these genes have changes (also called mutations) that prevent them from working properly.

In order for a person to have an amino acid disorder, he or she must have two changed copies of gene that causes a particular amino acid disorder. People with one amino acid gene change do not have an amino acid disorder. When an infant cannot burn an amino acid normally, several things happen:

  • Excess is converted in the body to other compounds, many of which are toxic.
  • There can be a deficiency of some compounds which are made from that amino acid—often things important for brain function.

Most Common Amino acid Disorders in Newborns:

Newborns mostly have the following amino acid disorders:

  • Phenylketonuria (PKU)
  • Maple Syrup Urine Disease (MSUD)
  • Homocystinuria (HCY)
  • Tyrosinemia, type I (TYR I)
  • Argininosuccinate Lyase Deficiency (ASA)
  • Citrullinemia (CIT)

Importance of Newborn screening in Amino Acids (AA) disorders:

Before babies go home from the nursery, they have a small amount of blood taken from their heel to test for amino acid disorders. Babies who screen positive for these disorders need follow-up tests done to confirm they have the condition. Immediate diagnosis and treatment of amino acid disorders is important for normal development and health.

Without prompt diagnosis and treatment, infants with amino acid disorders will develop varying degrees of developmental delay or intellectual disabilities, medical complications and may even experience death.

Signs and Symptoms of AA Disorders in Newborns:

The age that symptoms start and the types of symptoms that a person has vary. Many babies with amino acid disorders will appear normal at birth.

If not treated promptly, other newborns may develop symptoms such as:

  • Poor appetite
  • Sleepiness
  • Vomiting or irritability

If the condition is not treated promptly, babies can develop more serious problems including:

  • Breathing problems
  • Seizures
  • Swelling of the brain
  • Even coma or death


The only effective long term treatment for amino acid disorders is protein free diet. A long term treatment requires a special and permanent diet. This diet includes man-made infant formula; with low level of amino acids. Most important benefit of Newborn screening for Amino acid disorders is being able to start the diet before any damage is done. Newborns diagnosed with these disorders can live a relatively normal life, once they get used to the right diet.



  • Applegarth DA, Toone JR, Lowry RB (January 2000). “Incidence of inborn errors of metabolism in British Columbia.
  • Overview of Newborn Screening for Amino-acid Disorders for Parents. (2017). Indiana State Department of Health.
  • S Sanderson, A Green, M A Preece, H Burton (Nov 2006). The incidence of inherited metabolic disorder in the West Midland UK. Arch Dis Child. 91(11): 896–899.


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