X-linked adrenoleukodystrophy (X-ALD) Newborn Screening Reflex Test Program

X-linked adrenoleukodystrophy (X-ALD) is an inherited condition that affects the brain, nervous system, and adrenal glands due to a variant in the ABCD1 gene. People with X-ALD have problems metabolizing certain type of fats called very long chain fatty acids (VLCFAs).

Newborn screening detects potential X-ALD patients by looking for elevations of VLCFAs in the blood sample. If positive, the child will likely then go on for genetic confirmation of the disease.

If a child is positive for elevated VLCFAs on their initial X-ALD newborn screen and further testing or genetic testing reveals they are negative for X-ALD, the increased amount of VLCFA could potentially indicate another disease: a peroxisomal disorder called Zellweger spectrum disorder.

Peroxisomal biogenesis disorder-Zellweger spectrum disorder (PBD-ZSD) is a rare genetic disorder caused by mutations in one of 13 PEX genes and is characterized by an impaired peroxisome assembly, leading to multiple enzyme deficiencies affecting multiple organs.

X-ALD and PBD-ZSD disorders are inherited in an autosomal recessive manner and are caused by loss-of function variants in the relevant gene.

For this Next Generation Sequencing (NGS) test, sequencing is accomplished using exome capture probes (PGxome^®).

Copy number variants (CNVs) are also detected from NGS data. All CNVs are confirmed using another technology such as aCGH, MLPA, or PCR before they are reported.

This panel typically provides ≥98% coverage of all coding exons of the genes listed, plus ~10 bases of flanking noncoding DNA. We define coverage as ≥20X NGS reads or Sanger sequencing.

Due to known ABCD1 pseudogenes, exons 7-10 of the ABCD1 gene are analyzed via Sanger sequencing.

Pathogenic variants in the PEX genes account for nearly all cases of clinically and biochemically diagnosed PBD-ZSD. The overall sensitivity of this sequencing panel test is predicted to be over 95% for DNA substitutions (missense, nonsense, splicing pathogenic variants), small insertions and/or deletions (frameshift and splice-site pathogenic variants) and gross deletions and duplications. Over 99% of patients with X-linked adrenoleukodystrophy have ABCD1 pathogenic variants which can be detected by sequencing with copy number variant detection of gross deletions and duplications (http://www.x-ald.nl; Raymond et al. 2018. PubMed ID: 20301491).

Patients must meet ONE of the criteria below:

• Testing will be offered to children who screened positive for X-ALD on initial state newborn screen but negative for the disease after further laboratory testing.
• Testing will be offered to a blood relative (sibling, cousin) of a PBD-ZSD positive patient who was tested at PreventionGenetics.

Healthcare providers can request blood collection kits for the program by clicking the "Order Test Kits" button on this page.

Specimen Requirements

Collect 3 mL - 5 mL of whole blood in EDTA (purple top tube) or ACD (yellow top tube), minimum 1 mL for small infants.

Shipping and Handling Instructions

Label all specimen containers with the patient's name, date of birth, and/or ID number. At least two identifiers should be listed on specimen containers. Specimen deliveries are accepted Monday-Saturday for all specimen types. Holiday schedules will be posted on our website at least one week prior to major holidays.

Blood

At room temperature or refrigerated, a blood specimen is stable for up to 8 days. Include a refrigerated gel pack in the shipping container. Fresh blood specimens are preferred. If frozen, a blood specimen is stable for up to 1 month before shipping. Frozen blood specimens should be shipped frozen (preferably on dry ice) overnight.