Pycnodysostosis, a condition from which the painter Henri de Toulouse-Lautrec suffered, is a genetic disease characterized by short stature.
This rare disease, surprisingly, provides a window into how joints are destroyed by arthritis. It is caused by deficiency of an enzyme known as cathepsin K which hampers osteoclasts (the cells that break down bone in bone modeling and repair), leading to poor bone resorption and dense, brittle bones.
Cathepsin K's role in bone metabolism has largely been studied using mouse models, but a new study examines the enzyme's role in bone resorption in a human patient and shows that it is not required to break down bone. The study was published in the November issue of Arthritis & Rheumatism (http://www3.interscience.wiley.com/journal/76509746/home).
Led by Professor Yrjö T. Konttinen of Helsinki University Central Hospital in Helskinki, Finland , the study involved a 55-year-old female patient with pycnodysostosis who also developed psoriatic arthritis. Since the patient lacked cathepsin K due to her condition, researchers hypothesized that this would protect her from the bone erosions in the hands and feet normally seen in psoriatic arthritis. However, she did in fact develop extensive erosions and destructive bone changes in her hands. Blood analysis was conducted to examine the proteinases (enzymes that break down proteins) responsible for bone degradation as well as the cellular mechanisms of bone resorption.