TY - JOUR
T1 - Biochemical studies in fibroblasts to interpret variants of unknown significance in the abcd1 gene
AU - van de Stadt, Stephanie I. W.
AU - Mooyer, Petra A. W.
AU - Dijkstra, Inge M. E.
AU - Dekker, Conny J. M.
AU - Vats, Divya
AU - Vera, Moin
AU - Ruzhnikov, Maura R. Z.
AU - van Haren, Keith
AU - Tang, Nelson
AU - Koop, Klaas
AU - Willemsen, Michel A.
AU - Hui, Joannie
AU - Vaz, Frédéric M.
AU - Ebberink, Merel S.
AU - Engelen, Marc
AU - Kemp, Stephan
AU - Ferdinandusse, Sacha
N1 - Funding Information: Funding: Funded by grants from the Netherlands Organization for Scientific Research (grant/award number: 016.196.310, awarded to M.E.) and the Netherlands Organization for Health Research and Development (project number 543002004, awarded to S.K.). Publisher Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).
PY - 2021/12/1
Y1 - 2021/12/1
N2 - Due to newborn screening for X-linked adrenoleukodystrophy (ALD), and the use of exome sequencing in clinical practice, the detection of variants of unknown significance (VUS) in the ABCD1 gene is increasing. In these cases, functional tests in fibroblasts may help to classify a variant as (likely) benign or pathogenic. We sought to establish reference ranges for these tests in ALD patients and control subjects with the aim of helping to determine the pathogenicity of VUS in ABCD1. Fibroblasts from 36 male patients with confirmed ALD, 26 healthy control subjects and 17 individuals without a family history of ALD, all with an uncertain clinical diagnosis and a VUS identified in ABCD1, were included. We performed a combination of tests: (i) a test for very-long-chain fatty acids (VLCFA) levels, (ii) a D3-C22:0 loading test to study the VLCFA metabolism and (iii) immunoblotting for ALD protein. All ALD patient fibroblasts had elevated VLCFA levels and a reduced peroxisomal ß-oxidation capacity (as measured by the D3-C16:0/D3-C22:0 ratio in the D3-C22:0 loading test) compared to the control subjects. Of the VUS cases, the VLCFA metabolism was not significantly impaired (most test results were within the reference range) in 6/17, the VLCFA metabolism was significantly impaired (most test results were within/near the ALD range) in 9/17 and a definite conclusion could not be drawn in 2/17 of the cases. Biochemical studies in fibroblasts provided clearly defined reference and disease ranges for the VLCFA metabolism. In 15/17 (88%) VUS we were able to classify the variant as being likely benign or pathogenic. This is of great clinical importance as new variants will be detected.
AB - Due to newborn screening for X-linked adrenoleukodystrophy (ALD), and the use of exome sequencing in clinical practice, the detection of variants of unknown significance (VUS) in the ABCD1 gene is increasing. In these cases, functional tests in fibroblasts may help to classify a variant as (likely) benign or pathogenic. We sought to establish reference ranges for these tests in ALD patients and control subjects with the aim of helping to determine the pathogenicity of VUS in ABCD1. Fibroblasts from 36 male patients with confirmed ALD, 26 healthy control subjects and 17 individuals without a family history of ALD, all with an uncertain clinical diagnosis and a VUS identified in ABCD1, were included. We performed a combination of tests: (i) a test for very-long-chain fatty acids (VLCFA) levels, (ii) a D3-C22:0 loading test to study the VLCFA metabolism and (iii) immunoblotting for ALD protein. All ALD patient fibroblasts had elevated VLCFA levels and a reduced peroxisomal ß-oxidation capacity (as measured by the D3-C16:0/D3-C22:0 ratio in the D3-C22:0 loading test) compared to the control subjects. Of the VUS cases, the VLCFA metabolism was not significantly impaired (most test results were within the reference range) in 6/17, the VLCFA metabolism was significantly impaired (most test results were within/near the ALD range) in 9/17 and a definite conclusion could not be drawn in 2/17 of the cases. Biochemical studies in fibroblasts provided clearly defined reference and disease ranges for the VLCFA metabolism. In 15/17 (88%) VUS we were able to classify the variant as being likely benign or pathogenic. This is of great clinical importance as new variants will be detected.
KW - Adrenoleukodystrophy
KW - Fibroblasts
KW - Newborn screening
KW - Peroxisomal disorder
KW - Variants of unknown significance
UR - http://www.scopus.com/inward/record.url?scp=85120648796&partnerID=8YFLogxK
U2 - https://doi.org/10.3390/genes12121930
DO - https://doi.org/10.3390/genes12121930
M3 - Article
C2 - 34946879
SN - 2073-4425
VL - 12
JO - Genes
JF - Genes
IS - 12
M1 - 1930
ER -