In the present study, we showed that children with T1DM had higher levels of both anti-TPO Ab and anti-Tg Ab compared with healthy ones.
Also, T1DM children had higher prevalence of positive anti-TPO Ab than non-diabetic individuals.
It has been shown that T1DM has strong relationship with autoimmune disorders such as pernicious anemia, celiac disease, and idiopathic adrenal insufficiency. AIT is the most prevalent autoimmune disorders associated with T1DM [13
]. The reason for the high prevalence of some autoimmune disorders in these patients still remains undetermined. It may be due to a generally increased tendency to react against certain antigens, or a genetically impaired ability to acquire tolerance to some autoantigens, or certain common antigens present in the tissues of individuals prone to autoimmune diseases [18
According to some studies, common genetic determinants, mainly human leukocyte antigen (HLA) risk alleles[19
] or other genes outside the HLA region (i.e., CTLA4 gene and PTPN22 gene), could play a role[21
] in the occurrence of AIT in T1DM patients. Moreover, environmental factors such as stress, infection, trauma, smoking, drugs, and nutrition (especially increased iodine intake) seem to be involved[23
Both T1DM and AIT are organ-specific T-cell mediated diseases, and have similar patho-genesis, which involves T-cell infiltration resulting in dysfunction of the target organ[23
In the present study, the prevalence of positivity for anti-TPO Ab, anti-Tg Ab, and the prevalence of positivity for both antibodies and AIT (at least one positive Ab) in children with T1DM was 19, 11, 8.4, 22%, respectively, which was higher than those in non-diabetic individuals. In other studies, the prevalence of positive anti-TPO Ab in T1DM patients was reported to be 5.5-46.2%. The prevalence of high anti-Tg Ab in these patients ranged from 2.1 to 40%. In those studies, the prevalence of AIT in T1DM and healthy individuals was reported to be 11-46% and 1.4-11%, respectively. The wide range of these data can be explained by the difference in genetic factors, age, and sex of the studied population[24
], as well as the different methods for measurement of antibodies[9
]. Most studies that reported the low prevalence of AIT were conducted 1-2 decades ago, showing the lower sensitivity of the laboratory tests. Meanwhile, this finding might be a result of a real increase in the prevalence of AIT during the recent decades[9
]. Epidemiologic studies have shown higher incidence of AIT after elimination of iodine deficiency in endemic areas[23
In previous studies in Iran, the prevalence of positive anti-TPO Ab and anti-Tg Ab in T1DM patients were reported to be 27-39.6% and 27-34%, respectively[17
]. The lower prevalence of AIT in our study could be explained by the different age group of studied individuals in our study. The previous studies in Iran were conducted in adult population or had recruited some adults. However, the present study was conducted on children and showed comparable results with other studies performed in similar age group in northwestern part of Iran[24
] and other countries[28
]. Age dependent increase of AIT incidence has previously been described[28
The prevalence of clinical and subclinical thyroid dysfunction in T1DM patients is suggested to be 13.4-20%[25
], whilst the prevalence of hypothyroidism and hyper-thyroidism in the normal population is 5-10% and 1%, respectively[8
]. In the present study, there was no case of clinical thyroid dysfunction. However, subclinical hypothyroidism was present in 18% of both T1DM patients and the control group. In our study, the prevalence of subclinical hyperthyroidism in T1DM patients and non-diabetic subjects was 1% and 0.7%, respectively, which is consistent with the findings of previous studies[4
]. We found that diabetic patients with AIT had higher prevalence of subclinical hypothyroidism than diabetic patients without AIT (38.8% vs. 13.8%), which was statistically significant. Also, there was a positive correlation between thyroid dysfunction and AIT (data not shown). Therefore, the higher prevalence of subclinical hypothyroidism in T1DM patients could be explained by the high prevalence of AIT (22%) in these patients. As well as AIT, iodine deficiency can cause clinical or subclinical hypothyroidism[1
]. Unfortunately, we did not evaluate iodine status of the studied population and as a result, we could not investigate the role of iodine deficiency in the high prevalence of subclinical hypothyroidism.
In the present study, the prevalence of goiter in T1DM and non-diabetic individuals was 21% and 38%, respectively. The lower prevalence of goiter in T1DM patients in comparison with that in non-diabetic ones is in contrast with previous studies, which showed no difference in goiter prevalence between T1DM patients and control group[29
] or higher prevalence of goiter in patients with T1DM[32
]. Studies that showed higher thyroid volume and goiter prevalence in T1DM patients attributed this finding to the higher incidence of AIT in T1DM[34
]. However, we showed the higher prevalence of goiter in T1DM patients with AIT (38.8%) than in patients without AIT (17%). As stated before, we did not evaluate the iodine deficiency as a possible contributor of goiter. The higher levels of urinary iodine concentration in T1DM patients was previously reported[34
]. We classified children into goitrous and nongoitrous groups by inspection and palpation. The sensitivity and specificity of palpation is poor and it would be more accurate if we use thyroid ultrasonography to determine goiter size.
In our study, the prevalence of AIT in female patients with T1DM was higher than that in male T1DM patients. In the control group, the prevalence of AIT in male patients was higher than that in female ones. However, it should be stated that the differences were not statistically significant. Many studies found higher prevalence of positive thyroid autoantibodies in females[12
] and some studies reported similar prevalence in both genders[37
In agreement with previous studies[6
], in the current study, we found no relationship between HbA1c
, as a measure of metabolic control in diabetic patients, and AIT or thyroid dysfunction.