CD1 Gene Polymorphisms and Phenotypic Variability in X-Linked Adrenoleukodystrophy

X-linked adrenoleukodystrophy (X-ALD) is characterized by marked phenotypic variation ranging from adrenomyeloneuropathy (AMN) to childhood cerebral ALD (CCALD). X-ALD is caused by mutations in the ABCD1 gene, but no genotype-phenotype correlation has been established so far and modifier gene variants are suspected to modulate phenotypes. Specific classes of lipids, enriched in very long-chain fatty acids that accumulate in plasma and tissues from X-ALD patients are suspected to be involved in the neuroinflammatory process of CCALD. CD1 proteins are lipid- antigen presenting molecules encoded by five CD1 genes in human (CD1A-E). Association studies with 23 tag SNPs covering the CD1 locus was performed in 52 patients with AMN and 87 patients with CCALD. The minor allele of rs973742 located 4-kb downstream from CD1D was significantly more frequent in AMN patients (χ2 = 7.6; P = 0.006). However, this association was no longer significant after Bonferroni correction for multiple testing. The other polymorphisms of the CD1 locus did not reveal significant association. Further analysis of other CD1D polymorphisms did not detect stronger association with X-ALD phenotypes. Although the association with rs973742 warrants further investigations, these results indicate that the genetic variants of CD1 genes do not contribute markedly to the phenotypic variance of X-ALD

Functional genomic analysis unravels a metabolic-inflammatory interplay in adrenoleukodystrophy

X-linked adrenoleukodystrophy (X-ALD) is an inherited disorder characterized by axonopathy and demyelination in the central nervous system and adrenal insufficiency. Main X-ALD phenotypes are: (i) an adult adrenomyeloneuropathy (AMN) with axonopathy in spinal cords, (ii) cerebral AMN with brain demyelination (cAMN) and (iii) a childhood variant, cALD, characterized by severe cerebral demyelination. Loss of function of the ABCD1 peroxisomal fatty acid transporter and subsequent accumulation of very-long-chain fatty acids (VLCFAs) are the common culprits to all forms of X-ALD, an aberrant microglial activation accounts for the cerebral forms, whereas inflammation allegedly plays no role in AMN. How VLCFA accumulation leads to neurodegeneration and what factors account for the dissimilar clinical outcomes and prognosis of X-ALD variants remain elusive. To gain insights into these questions, we undertook a transcriptomic approach followed by a functional-enrichment analysis in spinal cords of the animal model of AMN, the Abcd1− null mice, and in normal-appearing white matter of cAMN and cALD patients. We report that the mouse model shares with cAMN and cALD a common signature comprising dysregulation of oxidative phosphorylation, adipocytokine and insulin signaling pathways, and protein synthesis. Functional validation by quantitative polymerase chain reaction, western blots and assays in spinal cord organotypic cultures confirmed the interplay of these pathways through IkB kinase, being VLCFA in excess a causal, upstream trigger promoting the altered signature. We conclude that X-ALD is, in all its variants, a metabolic/inflammatory syndrome, which may offer new targets in X-ALD therapeutics

Identification of novel SNPs of ABCD1, ABCD2, ABCD3, and ABCD4 genes in patients with X-linked adrenoleukodystrophy (ALD) based on comprehensive resequencing and association studies with ALD phenotypes

Adrenoleukodystrophy (ALD) is an X-linked disorder affecting primarily the white matter of the central nervous system occasionally accompanied by adrenal insufficiency. Despite the discovery of the causative gene, ABCD1, no clear genotype–phenotype correlations have been established. Association studies based on single nucleotide polymorphisms (SNPs) identified by comprehensive resequencing of genes related to ABCD1 may reveal genes modifying ALD phenotypes. We analyzed 40 Japanese patients with ALD. ABCD1 and ABCD2 were analyzed using a newly developed microarray-based resequencing system. ABCD3 and ABCD4 were analyzed by direct nucleotide sequence analysis. Replication studies were conducted on an independent French ALD cohort with extreme phenotypes. All the mutations of ABCD1 were identified, and there was no correlation between the genotypes and phenotypes of ALD. SNPs identified by the comprehensive resequencing of ABCD2, ABCD3, and ABCD4 were used for association studies. There were no significant associations between these SNPs and ALD phenotypes, except for the five SNPs of ABCD4, which are in complete disequilibrium in the Japanese population. These five SNPs were significantly less frequently represented in patients with adrenomyeloneuropathy (AMN) than in controls in the Japanese population (p = 0.0468), whereas there were no significant differences in patients with childhood cerebral ALD (CCALD). The replication study employing these five SNPs on an independent French ALD cohort, however, showed no significant associations with CCALD or pure AMN. This study showed that ABCD2, ABCD3, and ABCD4 are less likely the disease-modifying genes, necessitating further studies to identify genes modifying ALD phenotypes

Physiopathogénie et thérapie génique de l'adrénoleucodystrophie liée à l'X (ALD)

L'ALD est une maladie génétique caractérisée par une démyélinisation du SNC et une insuffisance surrénale. Elle présente une importante variabilité phénotypique. Aucune corrélation génotype/phénotype n'a pu être établie suggérant l'intervention de gènes modificateurs. La première partie de cette thèse a permis l'identification des gènes ABCD4 et BG1 jouant un rôle dans la sévérité de la maladie. La deuxième partie de ce travail a permis de montrer que l'expression restreinte du gène ABCD1 dans les oligodendrocytes permettait une correction des concentrations d'AGTLC dans le cerveau et la moelle de la souris ALD. Le manque de donneurs et les complications liées à la greffe de moelle osseuse allogénique ont conduit à développer une stratégie thérapeutique alternative, la greffe autologue de CSH génétiquement modifiées. Ce travail a permis de montrer la capacité des CD34+ transduites par un vecteur lentiviral avec l'ADNc ABCD1 à exprimer une protéine ALD fonctionnelle dans le SNC.X-ALD is a neurodegenerative disorder caracterized by CNS demyelinization and adrenal deficiency. X-ALD presents a marked phenotypic variability. No genotype-phenotype coorelation has been established which suggets the intervention of modifier genes. The first part of this thesis allowed to identify ABCD4 and BG1 genes playing a role in the severity of the disease. The second part of this work allowed to show that restricted expression of ABCD1 gene in oligodendrocytes corrects VLCFA levels in the brain and spinal cord of the ALD mouse. The lack of donors and complications linked to allogeneic bone marrow transplantation prompted to develop an alternative therapeutic strategy, the autologous transplantation of genetically modified hematopoïetic stem cells. This work allowed to demonstrate the capacity of human CD34+ cells transduced with a lentiviral vector expressing the ABCD1 gene to migrate in the SNC, differantiate into microglia and express a functional recombinant ALD protein.PARIS5-BU Méd.Cochin (751142101) / SudocSudocFranceF

Allelic analyses of the 23 tag SNPs genotyped in CCALD and AMN patients.

a<p>: The Fisher's exact test was used for SNP with a Minor Allele Frequency (MAF)<0.10.</p>b<p>: Permutation-based empirical <i>P</i> value were calculated for SNP showing a trend of association (<i>P</i> value<0.10).</p

Tagging of the <i>CD1 locus</i>.

<p>A) Allelic association results of the tag SNPs genotyped in CCALD and AMN patients: each black dot represents a tag SNP; -log₁₀<i>P</i> is plotted for each of the 21 tag SNPs; the five <i>CD1</i> genes are indicated by black boxes; B) LD between the corresponding tag SNPs: LD is represented by shades of grey as a function of r² values (black diamond for r²≥0.90, white diamond for r² = 0). Associated tag SNPs are marked with an asterisk.</p

Allelic analyses of <i>CD1D</i> and <i>CD1B</i> variants in the CCALD and AMN patients.

a<p>: The Fisher's exact test was used for SNP with a Minor Allele Frequency (MAF)<0.10.</p>b<p>: Permutation-based empirical <i>P</i> value were calculated for SNP showing a trend of association (<i>P</i> value<0.10).</p