Formation of calcium pyrophosphate crystals: biologic implications.

The formation of calcium pyrophosphate dihydrate (CPPD) crystals in articular cartilage marks the earliest known phase of CPPD deposition disease. Although the exact mechanisms through which these crystals form remains unknown, work over the last year has added useful details to our current paradigms of crystal nucleation and growth. Key advances include (1) progress in understanding pyrophosphate elaboration and its modifiers, (2) further characterization of the enzymes responsible for pyrophosphate elaboration, and (3) the discovery of an association between two seemingly unrelated metabolic risk factors for CPPD deposition disease.