# Periodontal Condition and Subgingival Microbiota Characterization in Subjects with Down Syndrome
## 4 Discussion
Since the endocrine system can modulate the immune system in a bidirectional manner [52] and, in a recent scoping review, on 29 selected articles, a positive relationship between hypothyroidism and periodontitis was found [53], thus the findings of the present study are totally unexpected. One possible explanation is that periodontitis patients are actually suffering subclinical hypothyroidism and/or they have not yet been properly diagnosed [54], and, this were true, the surveillance of hypothyroidism hormone function can be further supported in DS individuals. However, only speculations can be made at this point, since the previous hypothesis cannot be tested now. In the present study, patients with periodontitis were significantly older that those in periodontal health or gingivitis groups. This finding agrees with previous reports, that have pointed out that the prevalence of periodontal diseases in DS, as it occurs in the general population, increases with age [14; 15]. It is also relevant to highlight that the prevalence of periodontitis in DS individual is relatively high at a young age, ranging 58-96% in subjects younger that 35 years old [12]. As for other periodontitis as a manifestation of systemic diseases, periodontitis in DS individual presents more frequently with earlier onset, faster and generalized and more severe progression, as compared with individuals without a systemic immune compromised [16; 23]. A longitudinal study has also shown that periodontal pathogens can be frequently detected in DS subjects with periodontitis, for up to 6 months, despite periodontal treatment and frequent supportive periodontal care, suggesting a higher risk of progression and giving more relevance to supraginjai biofilm control as performed by the subject [55]. The importance of poor oral hygiene has been also emphasized in a recent study, suggesting a larger impact of a poor oral hygiene and an impaired immune response in the development of periodontal diseases in DS subjects [56]. However, the possible relevance of specific periodontal pathogens should not be discarded, since a recent 24-month study has even reported an association of high counts _of P. gingivis_ with risk of disease progression [57], although the study population did not include DS patients. The present study has clinically and microbiologically evaluated a large group of DS individuals. However, some limitations have to be acknowledged, being the main limitation that periodontal diagnosis was based on a partial-mouth clinical evaluation (Ramfjord teeth), with no radiographical evaluation, which may have underestimated disease levels. This approach was selected to ease the evaluation of the special patient population included in the study and knowing that partial-mouth recording systems may present adequate degrees of accuracy [58]. Additional limitations can also be listed: (i) in a cross-sectional design, causal associations cannot be established [59]; (ii) some confounding factors may have not been properly controlled, such as diet, life-style and habits, care givers support in oral hygiene; and (iii) differences in age and thyroid dysfunction may have impacted both clinical and microbiological findings.