Ilaria Bianchi

Genome-wide meta-analyses identify three loci associated with primary biliary cirrhosis

A genome-wide association screen for primary biliary cirrhosis risk alleles was performed in an Italian cohort. The results from the Italian cohort replicated IL12A and IL12RB associations, and a combined meta-analysis using a Canadian dataset identified newly associated loci at SPIB (P = 7.9 × 10−11, odds ratio (OR) = 1.46), IRF5-TNPO3 (P = 2.8 × 10−10, OR = 1.63) and 17q12-21 (P = 1.7 × 10−10, OR = 1.38).

Frequency of monosomy X in women with primary biliary cirrhosis

The mechanisms that cause the female predominance of primary biliary cirrhosis (PBC) are uncertain, but the X chromosome includes genes involved in immunological tolerance. We assessed the rate of X monosomy in peripheral white blood cells from 100 women with PBC, 50 with chronic hepatitis C, and 50 healthy controls, by fluorescence in-situ hybridisation. Frequency of X monosomy increased with age in all groups, but was significantly higher in women with PBC than in controls (p<0.0001); age-adjusted back-transformed mean frequencies were 0.050 (95% CI 0.046-0.055) in women with PBC, 0.032 (0.028-0.036) in those with chronic hepatitis C, and 0.028 (0.025-0.032) in controls. We suggest that haploinsufficiency for specific X-linked genes leads to female susceptibility to PBC.

The X chromosome and immune associated genes.

The X chromosome is known to contain the largest number of immune-related genes of the whole human genome. For this reason, X chromosome has recently become subject of great interest and attention and numerous studies have been aimed at understanding the role of genes on the X chromosome in triggering and maintaining the autoimmune aggression. Autoimmune diseases are indeed a growing heath burden affecting cumulatively up to 10% of the general population. It is intriguing that most X-linked primary immune deficiencies carry significant autoimmune manifestations, thus illustrating the critical role played by products of single gene located on the X chromosome in the onset, function and homeostasis of the immune system. Again, the plethora of autoimmune stigmata observed in patients with Turner syndrome, a disease due to the lack of one X chromosome or the presence of major X chromosome deletions, indicate that X-linked genes play a unique and major role in autoimmunity. There have been several reports on a role of X chromosome gene dosage through inactivation or duplication in women with autoimmune diseases, for example through a higher rate of circulating cells with a single X chromosome (i.e. with X monosomy). Finally, a challenge for researchers in the coming years will be to dissect the role for the large number of X-linked microRNAs from the perspective of autoimmune disease development. Taken together, X chromosome might well constitute the common trait of the susceptibility to autoimmune diseases, other than to explain the female preponderance of these conditions. This review will focus on the available evidence on X chromosome changes and discuss their potential implications and limitations.

Geoepidemiology, gender and autoimmune disease

Autoimmune diseases include more than 70 different disorders affecting over 5% of the population of the Western countries. They are mainly characterized by female predominance and have great impact on the quality of life of affected subjects. It is generally accepted that ADs are the result of a complex interaction between genetic and environmental factors; however the mechanisms involved in the loss of tolerance remain unknown. Studying the distribution of these conditions across various global regions and ethnic groups by means of geoepidemiology might readily provide epidemiological data and also advance our understanding of their pathogenesis. Indeed, geoepidemiology demonstrates that genetic susceptibility interacts with lifestyle and environmental factors, which include socioeconomic status, infectious agents (triggering or protective agents), environmental pollutants, and vitamin D (dependent on sunlight exposure), in determining the risk of developing autoimmunity and in the understanding of their female prevalence. To properly understand the geoepidemiology of human autoimmunity, it is important to consider the many pleiotropic factors which lead to its initiation. In most studies the focus has been on genetics and environment. However, in this review the focus is primarily on gender. Overall, autoimmune diseases are well known to have female predominance, but there is significant variation in geographic area. Further, the mechanisms that influence female predominance are relatively unknown. Hence the attempt in this review is to focus on these critical issues.

Immunochip analyses identify a novel risk locus for primary biliary cirrhosis at 13q14, multiple independent associations at four established risk loci and epistasis between 1p31 and 7q32 risk variants

To further characterize the genetic basis of primary biliary cirrhosis (PBC), we genotyped 2426 PBC patients and 5731 unaffected controls from three independent cohorts using a single nucleotide polymorphism (SNP) array (Immunochip) enriched for autoimmune disease risk loci. Meta-analysis of the genotype data sets identified a novel disease-associated locus near the TNFSF11 gene at 13q14, provided evidence for association at six additional immune-related loci not previously implicated in PBC and confirmed associations at 19 of 22 established risk loci. Results of conditional analyses also provided evidence for multiple independent association signals at four risk loci, with haplotype analyses suggesting independent SNP effects at the 2q32 and 16p13 loci, but complex haplotype driven effects at the 3q25 and 6p21 loci. By imputing classical HLA alleles from this data set, four class II alleles independently contributing to the association signal from this region were identified. Imputation of genotypes at the non-HLA loci also provided additional associations, but none with stronger effects than the genotyped variants. An epistatic interaction between the IL12RB2 risk locus at 1p31and the IRF5 risk locus at 7q32 was also identified and suggests a complementary effect of these loci in predisposing to disease. These data expand the repertoire of genes with potential roles in PBC pathogenesis that need to be explored by follow-up biological studies.

Y chromosome loss in male patients with primary biliary cirrhosis.

Sex chromosome abnormalities have been advocated to be involved in the striking female prevalence of primary biliary cirrhosis (PBC) and women with PBC manifest an increased X chromosome loss in peripheral blood mononuclear cells compared to age-matched healthy women. Our knowledge of the etiopathogenesis of autoimmunity in male patients remains, however, limited. Next to the possible role of androgens and their imbalances, the Y chromosome appears as a potential candidate for influence of the immune function in men. Herein we analyzed a population of male patients with primary biliary cirrhosis (n = 26) and healthy controls (n = 88) to define a potential association of disease and the loss of the Y chromosome. We demonstrate that Y chromosome loss indeed is higher in PBC males compared to healthy controls, and this phenomenon increases with aging. We were, thus, able to confirm the existence of an analogous mechanism in the male population to previously identified X haploinsufficiency in female patients with organ-specific autoimmune disease. We propose that this commonality might represent a relevant feature in the etiopathogenesis of autoimmune diseases that should be further investigated.

Keratin variants are overrepresented in primary biliary cirrhosis and associate with disease severity

Keratins (K) 8 and 18 variants predispose carriers to the development of end‐stage liver disease and patients with chronic hepatitis C to disease progression. Hepatocytes express K8/K18, whereas biliary epithelia express K8/K18/K19. K8‐null mice, which are predisposed to liver injury, spontaneously develop anti‐mitochondrial antibodies (AMA) and have altered hepatocyte mitochondrial size and function. There is no known association of K19 with human disease and no known association of K8/K18/K19 with human autoimmune liver disease. We tested the hypothesis that K8/K18/K19 variants associate with primary biliary cirrhosis (PBC), an autoimmune cholestatic liver disease characterized by the presence of serum AMA. In doing so, we analyzed the entire exonic regions of K8/K18/K19 in 201 Italian patients and 200 control blood bank donors. Five disease‐associated keratin heterozygous variants were identified in patients versus controls (K8 G62C/R341H/V380I, K18 R411H, and K19 G17S). Four variants were novel and included K19 G17S/V229M/N184N and K18 R411H. Overall, heterozygous disease‐associated keratin variants were found in 17 of 201 (8.5%) PBC patients and 4 of 200 (2%) blood bank donors (P < 0.004, odds ratio = 4.53, 95% confidence interval = 1.5–13.7). Of the K19 variants, K19 G17S was found in three patients but not in controls and all K8 R341H (eight patients and three controls) associated with concurrent presence of the previously described intronic K8 IVS7+10delC deletion. Notably, keratin variants associated with disease severity (12.4% variants in Ludwig stage III/IV versus 4.2% in stages I/II; P < 0.04, odds ratio = 3.25, 95% confidence interval = 1.02–10.40), but not with the presence of AMA. Conclusion: K8/K18/K19 variants are overrepresented in Italian PBC patients and associate with liver disease progression. Therefore, we hypothesize that K8/K18/K19 variants may serve as genetic modifiers in PBC. (HEPATOLOGY 2009.)

Genetics and epigenetics of primary biliary cirrhosis.

Primary biliary cirrhosis (PBC) has been considered a multifactorial autoimmune disease presumably arising from a combination of environmental and genetic factors, with genetic inheritance mostly suggested by familial occurrence and high concordance rate among monozygotic twins. In the last decade, genome-wide association studies, new data on sex chromosome defects and instabilities, and initial evidence on the role of epigenetic abnormalities have strengthened the crucial importance of genetic and epigenetic factors in determining the susceptibility of PBC. High-throughput genetic studies in particular have revolutionized the search for genetic influences on PBC and have the potential to be translated into clinical and therapeutic applications, although more biological knowledge on candidate genes is now needed. In this review, these recent discoveries will be critically summarized with particular focus on the possible steps that may transfer genetic and epigenetic knowledge to direct health benefits in patients with PBC.

Increased loss of the Y chromosome in peripheral blood cells in male patients with autoimmune thyroiditis

Multiple mechanisms have been proposed to explain the peculiar distribution of autoimmune thyroiditis (AIT) among women and men. Most attention has been focused on the detection of the role of estrogens and the X chromosome. Specifically, a potential role for X haploinsufficiency has been proposed in the female patient population and an association with the disease has been confirmed. Our knowledge of the etiopathogenesis of autoimmunity in male patients remains, however, limited. Next to the possible role of androgens and their imbalances, the Y chromosome appears as a potential candidate for influence of the immune function in men. Herein we analyzed a population of male patients with AIT (n=31) and healthy controls (n=88) to define a potential association of disease and the loss of the Y chromosome. Y chromosome loss increases in AIT compared to unaffected subjects; these phenomenon increases with aging as expected, however, the degree of loss is significantly increased in the patient population compared to the healthy controls. We were, thus, able to confirm the existence of an analogous mechanism in the male population to previously identified X haploinsufficiency in female patients with AIT. We propose that this commonality might represent a relevant feature in the etiopathogenesis of AIT that should be further investigated.

Genetic association of Fc receptor-like 3 polymorphisms with susceptibility to primary biliary cirrhosis: ethnic comparative study in Japanese and Italian patients

A functional variant in the Fc receptor-like 3 (FCRL3) gene is associated with the susceptibility to several autoimmune diseases. In this study, we examined whether the FCRL3 is associated with susceptibility to primary biliary cirrhosis (PBC) by comparing the two different ethnic groups, Japanese and Italians. We enrolled 232 patients with PBC and 230 controls in Japanese, and 216 PBC and 180 controls in Italians. Minor allele frequency of fcrl3_3 (-169 T>C) in the patients with PBC and controls was 0.20 and 0.09 in Japanese and 0.24 and 0.21 in Italians, respectively. We found a significant association of fcrl3_3 with PBC only in Japanese (P = 9.64 × 10(-7) ). These findings support the presence of common FCRL3-related pathological pathways in several autoimmune diseases, especially in Asians.