Amino Acid Disorders

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Brief Description

These 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.  Newborns identified to be at risk for an amino acid disorder are referred to a contracted medical center for diagnostic evaluation.
The list of amino acid disorders that we screen for are:
Argininemia (ARG, arginase deficiency)
Argininosuccinate acidemia (ASA, argininosuccinase)
Citrullinemia type I (CIT-I, argininosuccinate synthetase)
Citrullinemia type II (CIT-II, citrin deficiency)
Defects of biopterin cofactor biosynthesis (BIOPT-BS)
Defects of biopterin cofactor regeneration (BIOPT-RG)
Homocystinuria (HCY, cystathionine beta synthase)
Hyperphenylalaninemia (H-PHE)
Hypermethioninemia (MET)
Maple syrup urine disease (MSUD, branched-chain ketoacid dehydrogenase)
Phenylketonuria (PKU, phenylalanine hydroxylase)
Tyrosinemia type I (TYR-1, fumarylacetoacetate hydrolase) *
Tyrosinemia type II (TYR-II, tyrosine aminotransferase)
Tyrosinemia type III (TYR-III, hydroxyphenylpyruvate dioxygenase)

         * There is a lower probability of detection of this disorder during the immediate newborn period.

Laboratory Unit

Newborn Screening

Methodology

Tandem Mass Spectrometry (MSMS)

Specimen Collection

Missouri newborn screening samples must only be collected on the FDA approved blood collection forms that are provided by the MSPHL and must be pre-purchased at a cost of $65 per collection form.  The optimum collection time is between 24 and 48 hours-of-age.  The instructions for collecting the samples are listed on the back of the collection form.  All 5 circles on the filter paper need to be filled with blood  from one side and then air dried for at least 3 hours in a horizontal position without allowing the blood to touch any surface during drying, including other parts of the card (see image).
See "Rules for Collection".

Storage/Transport

Store the dried blood samples at room temperature in the envelopes provided by the MSPHL and transport within 24 hours of collection.

Acceptable Specimen
Type(s)

Initial Screen (the red form) or Repeat Screen (the green form)



Test Request Form(s)

Included in kit

Possible Results

Normal: The final newborn screening reports are mailed to the submitter and physician of record.
Low Risk: Repeat the newborn screen. If, however, the infant is sick or displays signs of metabolic distress, the physician may wish to conduct diagnostic testing instead of, or in addition to the repeat screen. The final newborn screening reports are mailed to the submitter and physician of record.
Moderate/High Risk: Diagnostic testing and consultation with a metabolic specialist is needed. Final results are phoned and faxed to physician/health care provider and appropriate follow up center. Follow up centers are contracted by the Department of Health and Senior Services for follow up tracking, testing, diagnosis, and counseling.

Reference Range

Reference Range Table

Unacceptable Conditions

Poor Quality Specimens

Interfering Substances

NICU Guidelines and Key for NBS

Specimen collection prior to 24 hours of age, prematurity, and illness can all affect the newborn screening results.  “No Result” is reported on those specimens collected before 24 hours of age.  TPN feeding can elevate several of the amino acids above the designated cutoffs. If the infant is on TPN, we ask that it be noted on the requisition form to help us reduce the reporting of false positive results. Not all TPN fed infants will get abnormal results, but if they do, we ask that a repeat newborn screening sample be collected 48 hours after the TPN has been discontinued.

Result Reported

1 to 3 working days after receipt of specimen

Fees

$65 charge - for full panel of screening disorders

CPT Codes

83789

LOINC/SNOMED Codes

N/A

Additional Information

Prevalence of Disorder:  1:8,000 in Missouri

Feeding Effect:  Protein feeding is helpful in detecting the condition as it challenges the metabolic pathways involved and causes the identifying markers to elevate above the normal cutoff levels allowing detection of the disorder. The optimum collection time for the newborn screening sample is between 24 and 48 hours after birth, and sufficient protein feeding has taken place by then. This includes TPN feeding, which contains amino acids.

Treatment:  Treatment of these disorders is accomplished with dietary restriction of the offending amino acid(s) and sometimes medication. Urea cycle disorders will require treatment with low protein diets and medications to prevent hyperammonemia and remove toxic compounds. Infants with neonatal presentations of a urea cycle disorders represent medical emergencies and outcomes may be variable. These patients typically require aggressive treatment with hemodialysis.