About the test
Metabolic disorders are rare and are usually inherited from one or both parents. Sometimes these genetic disorders are not inherited but first appear in this baby. Each disorder is caused by a different genetic condition and affects different processes in the body.
The current conditions screened for are:
- Amino acid disorders (for example PKU and MSUD)
- Fatty acid oxidation disorders (for example MCAD)
- Congenital hypothyroidism (CH)
- Cystic fibrosis (CF)
- Congenital adrenal hyperplasia (CAH)
- Biotinidase deficiency
Severe combined immune deficiency (SCID).
If your baby has one of these disorders, you will receive information about the disorder and how to treat it from a paediatrician. For more information see the pamphlet Your Newborn Baby's Blood Test.
What are metabolic disorders?
Metabolic disorders are rare inherited disorders in which pathways that produce certain biochemicals malfunction. These pathways are like assembly lines in a human cell. A blockage at any point along the assembly line can lead to a build-up of toxic chemicals in the cell or lack of an important biochemical in the body.
Nearly every metabolic disorder has several forms, which vary in age of onset, clinical severity and mode of inheritance. Many lead to major organ dysfunction or failure. Without treatment, their presentation ranges from mild disorders to acute life-threatening diseases.
Table of disorders with cause, treatment, and incidences
The disorders, cause, treatment and incidence rates for New Zealand are:
|Congenital hypothyroidism||The thyroid is missing, not functioning or in the wrong place.
Can lead to slow growth and developmental delay.
|Medication (thyroid hormone)||1 in 4,000 babies (about 15 babies a year)|
|Cystic fibrosis||A defective gene and its protein product leads to thick sticky mucus.||Medication Physiotherapy||1 in 7,000 babies (about 8 babies a year)|
|Amino Acid disorders eg Phenylketonuria (PKU) and disorders listed below*||An enzyme is missing.
eg PKU - without this enzyme an amino acid (called phenylalanine) rises to harmful levels and can lead to developmental delay.
|Special diet||1 in 12,000 babies (about 5 babies a year)|
|Fatty acid oxidation disorders eg Medium chain acyl-CoA dehydrogenase deficiency or MCADD and disorders listed below**||An enzyme is missing.
Without these enzymes energy cannot be converted from fats and can lead to coma and death.
|Regular feeding (avoidance of fasting)||1 in 12,000 babies (about 5 babies a year)|
|Congenital Adrenal Hyperplasia (CAH)||An enzyme is missing in the adrenal gland. In severe forms leads to ambiguous genitalia in girls and salt/hormonal imbalances in both sexes.||Steroid medication||1 in 20,000 babies (about 3 babies a year)|
|Galactosemia||A defective enzyme prevents normal use of milk sugar leading to jaundice, cataracts and life-threatening illness.||Special diet||1 in 100,000 (about 1 baby every 2 years)|
|Biotinidase deficiency||An enzyme is missing resulting in a deficiency in biotin. This deficiency can lead to seizures, hearing loss and developmental delay.||Vitamin H (biotin)||1 in 150,000 (about 1 baby every 3 years)|
|Severe combined immune deficiency (SCID)||A lack of cells that are essential for immunity.||Antibiotics, isolation precautions and bone marrow transplant||1 in 50,000 to 1 in 60,000 (about 1 baby per year)|
*Other amino acid disorders include:
- Argininosuccinic aciduria (argininosuccinate lyase deficiency)
- Citrullinaemia (argininosuccinate synthetase deficiency, citrin deficiency)
- Glutaric acidaemia type I (glutaryl-CoA dehydrogenase deficiency)
- Homocystinuria (cystathionine beta-synthase deficiency)
- Isovaleric acidaemia (isovaleryl-CoA dehydrogenase deficiency)
- Methylmalonic acidurias (mutase deficiency, CblA, CblB, CblC, CblD defects)
- Propionic acidaemia (propionyl-CoA carboxylase deficiency)
- Maple syrup urine disease (branched chain ketoacid dehydrogenase deficiency).
**Fatty acid oxidation disorders include:
- CACT (carnitine acylcarnitine translocase deficiency)
- CPT-I (carnitine palmitoyltransferase-I deficiency)
- CPT-II (carnitine palmitoyltransferase-II deficiency)
- LCHAD (3-hydroxy long-chain acyl-CoA dehydrogenase deficiency)
- TFP (trifunctional protein deficiency)
- MADD (multiple acyl-CoA dehydrogenase deficiency)
- MCAD (medium-chain acyl-CoA dehydrogenase deficiency)
- VLCAD (very-long-chain acyl-CoA dehydrogenase deficiency).
Changes to the disorders screened for
From time to time new disorders are considered for inclusion in the screening programme and current disorders considered for removal, in accordance with a comprehensive process set out in the screening programme policy framework.
Conditions no longer being screened for
In 2015 new evidence was assessed and it was agreed by clinical experts and the NSU that a group of rare disorders (carboxylase deficiencies) should no longer be screened for. Screening for these disorders was found to have no clinical benefit for the child.
In August 2015 the Newborn Metabolic Screening Programme stopped screening for the following conditions:
- 3 methylcrotonyl-CoA carboxylase deficiency (3MCCC)
- 3-hyroxy-3-methylglutaryl-(HMG)-CoA lyase deficiency
- multiple CoA carboxylase deficiency
- 3-methylglutaconyl-CoA-hydratase deficiency
- beta-ketothiolase deficiency
- 2-methyl-3-hydroxybutyryl CoA dehydrogenase deficiency.
In April 2017 it was determined that the criteria for screening suitability were not being met for two conditions due to the high number of false positive results and lack of true cases detected.
From mid June 2017:
- the Newborn Metabolic Screening Programme will cease screening for carnitine transport defect
- screening for tyrsosinemia will be suspended while work is done on the cost-effectiveness of a different screening test.