In agreement with recent findings, our data showed an association of the
PTPN22 1858T allele with T1D in the Spanish population (Table
1). Despite the fact that T1D is an autoimmune disease which does not show sex-bias (gender distribution in our Spanish diabetic population: 50.3% women vs. 49.7% men), Kahles et al [
20] reported an association of
PTPN22 1858T allele only in German T1D females. However, we cannot conclude that this susceptibility factor is exclusively associated with female patients, as it has been proposed, because we could not find a significant difference between diabetic female and male patients (Table
1). This result agrees with several studies which do not show a gender-specific effect [
12,
14,
17,
18,
24]. The female association found by Kahles et al [
20] and the male association reported by Herman et al [
25] could be due to spurious effects; however, the analysis in our pediatric-onset patients supports a preferential association in T1D females (Table
2). This age- and gender-dependent association could explain previous results, given that the sex-bias is evidenced only in early-onset patients, but the observed association warrants replication in independent populations. Recent studies have revealed that LYP increases phosphatase activity when allele 1858T is present [
26]. This gain of function mutant hypothetically suppresses T cell signaling more efficiently and leads to a failure in apoptosis of autoreactive T cells and to an insufficient activity of regulatory T cells [
27]. Given than women have higher absolute numbers of CD4 lymphocytes than men and higher levels of Th1 cytokines [
28], this would justify that the observed role of the
PTPN22 polymorphism is mainly evidenced in girls. Furthermore, in the group with disease onset after 15 years old no gender differences could be established and both female and male patients compared with controls showed OR values of 1.70 (Table
2). In summary, the reasons for sex differences in early onset in T1D is a complex process which remains unclear and could mean that there is an interacting factor with PTPN22 yet to be identified, the effect of sex hormones or epigenetic modifications of DNA could explain this gender-dependent association.
In a recent study, Steck et al [
24] described a significant association after stratification by HLA-DRB1 genotypes only in the non-DRB1*03/04 subgroup. However, as they recognize, the lack of association in the high-risk HLA-DRB1 genotype was probably due to compromised statistical power. Moreover, their linear regression analyses did not reveal interaction between
PTPN22 genotypes and the aforementioned HLA genotype; therefore, they suggest that
PTPN22 influences T1D risk in all HLA subgroups. The stratification by HLA-DRB1 alleles in our cohort showed no different frequency of the
PTPN22 1858T allele in any of the patient subgroups. These data suggest that the susceptibility conferred by the
PTPN22 gene is an independent factor of the HLA effect and patients carrying the
PTPN22 1858T allele have an increased risk for T1D development independent of this important genetic factor implicated in the disease.