Genetic Architecture of Vitamin B-12 and Folate Levels Uncovered Applying Deeply Sequenced Large Datasets
PLOS GENETICS
Authors: Grarup, Niels; Sulem, Patrick; Sandholt, Camilla H.; Thorleifsson, Gudmar; Ahluwalia, Tarunveer S.; Steinthorsdottir, Valgerdur; Bjarnason, Helgi; Gudbjartsson, Daniel F.; Magnusson, Olafur T.; Sparso, Thomas; Albrechtsen, Anders; Kong, Augustine; Masson, Gisli; Tian, Geng; Cao, Hongzhi; Nie, Chao; Kristiansen, Karsten; Husemoen, Lise Lotte; Thuesen, Betina; Li, Yingrui; Nielsen, Rasmus; Linneberg, Allan; Olafsson, Isleifur; Eyjolfsson, Gudmundur I.; Jorgensen, Torben; Wang, Jun; Hansen, Torben; Thorsteinsdottir, Unnur; Stefansson, Kari; Pedersen, Oluf
Abstract
Genome-wide association studies have mainly relied on common HapMap sequence variations. Recently, sequencing approaches have allowed analysis of low frequency and rare variants in conjunction with common variants, thereby improving the search for functional variants and thus the understanding of the underlying biology of human traits and diseases. Here, we used a large Icelandic whole genome sequence dataset combined with Danish exome sequence data to gain insight into the genetic architecture of serum levels of vitamin B-12 (B-12) and folate. Up to 22.9 million sequence variants were analyzed in combined samples of 45,576 and 37,341 individuals with serum B-12 and folate measurements, respectively. We found six novel loci associating with serum B-12 (CD320, TCN2, ABCD4, MMAA, MMACHC) or folate levels (FOLR3) and confirmed seven loci for these traits (TCN1, FUT6, FUT2, CUBN, CLYBL, MUT, MTHFR). Conditional analyses established that four loci contain additional independent signals. Interestingly, 13 of the 18 identified variants were coding and 11 of the 13 target genes have known functions related to B-12 and folate pathways. Contrary to epidemiological studies we did not find consistent association of the variants with cardiovascular diseases, cancers or Alzheimer's disease although some variants demonstrated pleiotropic effects. Although to some degree impeded by low statistical power for some of these conditions, these data suggest that sequence variants that contribute to the population diversity in serum B-12 or folate levels do not modify the risk of developing these conditions. Yet, the study demonstrates the value of combining whole genome and exome sequencing approaches to ascertain the genetic and molecular architectures underlying quantitative trait associations.
Dehydroepiandrosterone up-regulates the Adrenoleukodystrophy-related gene (ABCD2) independently of PPAR alpha in rodents
BIOCHIMIE
Authors: Gueugnon, F.; Gondcaille, C.; Leclercq, S.; Bellenger, J.; Bellenger, S.; Narce, M.; Pineau, T.; Bonnetain, F.; Savary, S.
Abstract
X-linked adrenoleukodystrophy (X-ALD) is a neurodegenerative disease caused by mutations in the ABCD1 gene, which encodes a peroxisomal ABC transporter, ALDP, supposed to participate in the transport of very long chain fatty acids (VLCFA). The adrenoleukodystrophy-related protein (ALDRP), which is encoded by the ABCD2 gene, is the closest homolog of ALDP and is considered as a potential therapeutic target since functional redundancy has been demonstrated between the two proteins. Pharmacological induction of Abcd2 by fibrates through the activation of PPAR alpha has been demonstrated in rodent liver. DHEA, the most abundant steroid in human, is described as a PPAR alpha activator and also as a prohormone able to mediate induction of several genes. Here, we explored the in vitro and in vivo effects of DHEA on the expression of peroxisomal ABC transporters. We show that Abcd2 and Abcd3 but not Abcd4 are induced in primary culture of rat hepatocytes by DHEA-S. We also demonstrate that Abcd2 and Abcd3 but not Abcd4 are inducible by an 11-day treatment with DHEA in the liver of male rodents but not in brain, testes and adrenals. Finally and contrary to Abcd3, we show that the mechanism of induction of Abcd2 is independent of PPAR alpha. (C) 2007 Elsevier Masson SAS. All rights reserved.