Human leukocyte antigen in sickness and in health : Ankylosing spondylitis and HLA in Sweden

Abstract: The human leukocyte antigen (HLA) plays a major role in keeping us healthy, but some of the HLA alleles can contribute to disease susceptibility. One example is HLA-B'27, which confers increased susceptibility of ankylosing spondylitis and represents one of the strongest genetic associations found in any common human disease. Ankylosing spondylitis shows a strong sex ratio skew (2-3:1 male to female) and studies confirm the existence of sexual-dimorphism in the presentation of this disease. The genetic predisposition for this, however, has not previously been studied. A Swedish ankylosing spondylitis population was sequenced with a targeted array to investigate the existence of sex-specific associations. RUNX3 was revealed to be associated in males by a univariate test, while aggregate tests revealed the HLA gene MICB to be associated in females. Functional validation demonstrated that the risk variants in RUNX3 increase expression, and MICB changed the transcription factor binding sites. Interestingly, since the disease involves bone changes, both RUNX3 and one of the MICB variants had effect in the bone cell line, SaOS-2.In order to help researchers obtain more controls for HLA analysis, an HLA allele bioresource (SweHLA) was generated from 1,000 Swedish genomes. The alleles were typed with three to four HLA typing software programs and results were combined by an n-1methodology. This produced high quality alleles where the bias from each software program was diminished.The methodology from SweHLA was utilised to study HLA in ankylosing spondylitis. To investigate both sex-specific predisposition and HLA-B'27 independence, samples were subdivided into two populations (one population with mixed HLA-B'27 positive and negative samples and one with only HLA-B'27 positive samples) that in turn were grouped by sex. In the mixed population, several alleles were replicated from previous studies. This study also revealed three female-specific alleles, two of which were new and one that had previously been associated to the severity of radiological changes. The HLA-B'27 population revealed a previously unknown protective allele, HLA-A'24:02. Through deeper examination of the HLA-B'27 population, two amino acids in HLA-A, position 119 in the whole set and position 180 in the male set, were revealed to be protective.This thesis brings new insight into the genetic predisposition for a sex-skewed disease, demonstrating how sexual-dimorphism can be reflected in the genetic predisposition, hopefully leading to more similar studies. It also highlights the importance of methodology and demonstrate the drastic biases that can be imparted by software programs.