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

Program Overview

Retrophin has partnered with PreventionGenetics to offer a no-cost genetic testing program to qualifying patients to help identify peroxisome biogenesis disorder-Zellweger spectrum disorder (PBD-ZSD) and other disorders within the states offering X-linked adrenoleukodystrophy (X-ALD) newborn screening programs.

Testing will be offered to children who screened positive for X-ALD on initial state newborn screen but negative for disease after further laboratory testing.

Retrophin sponsored reflex testing will include:

  • Reanalysis of ABCD1 gene at PreventionGenetics for verification
  • Panel testing with whole exome sequencing (WES) will be performed on the genes listed to the right. All listed genes are associated with diseases with elevated VLCFAs.

Clinical Features

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.

Newborn screening for X-ALD is being conducted in 15 States with additional states being added in 2020.

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.

Genetics

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.

Testing Strategy

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.

Clinical Sensitivity

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).

Criteria For Test

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.

Ordering

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

  1. Determine if the individual meets eligibility criteria and discuss the test.
  2. Order the test and collect a blood specimen and ship them to the lab.
  3. The genetic test will be processed at PreventionGenetics and the results will be sent to the ordering healthcare provider about 21 days after the lab receives the specimen and all appropriately completed paperwork. The ordering healthcare provider will discuss the results with the patient and / or caregiver.

Specimen Collection and Shipping

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

DO NOT FREEZE. During hot weather, include a frozen ice pack in the shipping container. Place a paper towel or other thin material between the ice pack and the blood tube. In cold weather include an unfrozen ice pack in the shipping container as insulation. At room temperature, blood specimen is stable for up to 48 hours. If refrigerated, blood specimen is stable for up to one week.