Molecular Differences between Chronic and Aggressive Periodontitis

The 2 major forms of periodontitis, chronic (CP) and aggressive
(AgP), do not display sufficiently distinct histopathological
characteristics or microbiological/immunological features. We used
molecular profiling to explore biological differences between CP
and AgP and subsequently carried out supervised classification
using machine-learning algorithms including an internal validation.
We used whole-genome gene expression profiles from 310 healthy' or
diseased' gingival tissue biopsies from 120 systemically healthy
non-smokers, 65 with CP and 55 with AgP, each contributing with 2
diseased' gingival papillae (n = 241; with bleeding-on-probing,
probing depth 4 mm, and clinical attachment loss 3 mm), and, when
available, a healthy' papilla (n = 69; no bleeding-on-probing,
probing depth 4 mm, and clinical attachment loss 4 mm). Our
analyses revealed limited differences between the gingival tissue
transcriptional profiles of AgP and CP, with genes related to
immune responses, apoptosis, and signal transduction overexpressed
in AgP, and genes related to epithelial integrity and metabolism
overexpressed in CP. Different classifying algorithms discriminated
CP from AgP with an area under the curve ranging from 0.63 to 0.99.
The small differences in gene expression and the highly variable
classifier performance suggest limited dissimilarities between
established AgP and CP lesions. Future analyses may facilitate the
development of a novel, intrinsic' classification of periodontitis
based on molecular profiling.