The present study explored the association between parental autoimmune diseases and AD in their children. Our novel findings illustrated two main points. Firstly, parental AD, asthma, RA and psoriasis increased the risk of AD development in children before 5 years old. Furthermore, the subgroup analysis presented different odds ratios of parental diseases between the sexes of children. Parental RA was more prevalent in male children with AD, while parental psoriasis was more prevalent in female children with AD.
The pathophysiologic mechanism of maternal diseases may be explained by the exposure of IgE autoantibodies during pregnancy. One Swedish study mentioned that higher prevalence of asthma was noted in children born to mothers with SLE during pregnancy.4 Another study found that maternal dermatologic and digestive autoimmune diseases were closely associated with subsequent AD in their offspring.6 Though the mechanism of relationship between AD and autoimmune diseases remains unclear, it is found that 65% of the patients with SLE had higher level of IgE autoantibodies 13, which was also prevalent in 50–60% of patients with RA.14 Studies suggested that elevation of IgE level and self-reactive T cell during pregnancy could induce autoreactivity in early infancy and subsequently increase the risk of developing AD. 15 16
Additionally, our study also found that both maternal and paternal allergic diseases could be the risk factors, which implied that genes effect also played an important role in AD. Filaggrin is a fundamental protein of skin barrier, and mutation of filaggrin (gene R501X and 2282del4) could be perceived as one of strongest predictors for AD.17 In other GWAS(genome-wide association studies), filaggrin was not only listed as a characterized risk locus of AD, but its effect on genomic printing was prove to be equal between maternal and paternal alleles.18 However, filaggrin mutations were more frequent in women,18 which would lead to closer relationship between maternal atopic diseases and children AD. The adjusted odds ratios (p value) of paternal diseases exposure that compared with maternal disease exposure (as reference group) were showed in Supplemental Table 3 (boys) and Supplemental Table 4 (girls). When compared with maternal AD exposure, the adjusted odds ratio of paternal AD exposure is 0.903 (p < 0.0001) and 0.898 (p < 0.0001) for childhood AD in boys and girls, respectively. Our result showed significant difference and was consistent with the hypothesis.
The distinguishing feature of our study is the subgroup analysis of children’s sexes, which showed the different risk factors for boys and girls, respectively. Studies have presented that early-onset AD was more prevalent in boys, while more females would develop AD after puberty. 19 Though there are many possible mechanisms, sex hormones may explain the difference of onset and progression between sexes. Studies have mentioned that level of dehydroepiandrosterone (DHEA), precursor of testosterone, was lower in boys because it was controlled by an X-linked gene. Moreover, in the study by Zhang et al, the AD-driven cytokines such as interleukins 4 and 11 were found to promote the expression of enzyme for DHEA. This would increase androgen synthesis in sebocytes and decrease total amounts of triglyceride, which could lead to disruption of epidermal permeability barrier.20 21 Adversely, higher level of estrogen was perceived as a protective factor for AD because of its function of reconstitution in skin barrier. Though our study mainly focused on AD development before 5 years old, it is also noted that increased estrogen and progesterone levels after puberty stimulated the activity of Th2 cells, which could lead to exacerbation of AD during premenstrual phase and pregnancy, and impact the development of immune system of the fetus.15 21
Lastly, both RA and psoriasis were found to be associated with AD in several studies. RA and AD shared a similar immune mechanism, including the increased activity of Th17 cells and dysfunction of regulatory T cells.22 While most of the studies considered AD as a Th2-predominating disease in acute phase, the switch to Th1 was noted during the chronic period, which was also found in AD patient who developed RA.23 24 On the other hand, although several studies have identified the common susceptibility loci of AD and psoriasis, the coexistance of these diseases still remained controversial because of their difference in immune pathway.10 25As a result, studies suggested that subtypes of AD should also be taken into consideration because there are difference in prominent cytokines among these subtypes.26
The study has a number of strengths. The link between perinatal data in the National Birth Registry and NHIRD enabled us to obtain a real-world data across generation. The participants were drawn from a population-based and highly representative computerized database of medical records. This allowed us to perform our analysis with a real-life setting in an unselected patient population. We took advantage of the detailed medical record in NHIRD and used the strict definitions at least three outpatient visits or one hospital admission with ICD-9 691.27 Additionally, we took a variety of autoimmune diseases into consideration and divided the confounding factors into paternal, maternal and parental(both) influences to compare the effects between parents. Lastly, the subgroup analysis showed different risk factors for AD in boys and girls.
Some limitations should be taken into consideration in this study. First, though the AD patients with ICD-9 code was physician-diagnosed, the lack of confirmation of skin test or sIgE assay still could result in misclassification bias. Hence, we added “at least three outpatient visits or one hospital admission” to the definition of being diagnosed with AD. Second, autoimmune diseases are usually companied with long-term use of immunosuppressive drugs such as corticosteroid, hydroxychloroquine and TNFi (tumor necrosis factor inhibitor). Perinatal exposures to them may give rise to the change in maternal immune system 28 29, and their effects on subsequent AD development in patients’ offspring should be well discussed in further studies. Lastly, data on parental smoking history and socioeconomic status was not recorded in the NHIRD, despite the fact that these parental exposures could be important risk factors for childhood atopic diseases.30 Consequently, we replaced smoking history as chronic obstructive pulmonary disease and listed it as one of the confounding factors.
In conclusion, this 14-year case-control study demonstrated that both paternal and maternal autoimmune diseases are risk factors for atopic dermatitis in their children, especially seen with parental RA and psoriasis. There are also different risk factors between sexes: parental RA for boys and parental psoriasis for girls. Therefore, further studies are needed to investigate the underlying mechanisms in genes and immunology. It is recommended that both obstetricians and pediatricians be aware of the risk of developing childhood AD in children to the patients with autoimmune diseases and support the pregnant patients with adequate medical treatment.