Abstract

Background: WNT signaling plays a major role in bone and cartilage metabolism. Impaired WNT/β-catenin signaling leads to early-onset osteoporosis, but specific features in bone and other tissues remain inadequately characterized. We have identified two large Finnish families with early-onset osteoporosis due to a heterozygous WNT1 mutation c.652T > G, p.C218G. This study evaluated the impact of impaired WNT/β-catenin signaling on spinal structures.

Methods: Altogether 18 WNT1 mutation-positive (age range 11–76 years, median 49 years) and 14 mutation-negative subjects (10–77 years, median 43 years) underwent magnetic resonance imaging (MRI) of the spine. The images were reviewed for spinal alignment, vertebral compression fractures, intervertebral disc changes and possible endplate deterioration. The findings were correlated with clinical data.

Results: Vertebral compression fractures were present in 78% (7/9) of those aged over 50 years but were not seen in younger mutation-positive subjects. All those with fractures had several severely compressed vertebrae. Altogether spinal compression fractures were present in 39% of those with a WNT1 mutation. Only 14% (2/14) mutation-negative subjects had one mild compressed vertebra each. The mutation-positive subjects had a higher mean spinal deformity index (4.0 ± 7.3 vs 0.0 ± 0.4) and more often increased thoracic kyphosis (Z-score > + 2.0 in 33% vs 0%). Further, they had more often Schmorl nodes (61% vs 36%), already in adolescence, and their intervertebral discs were enlarged.

Conclusion: Compromised WNT signaling introduces severe and progressive changes to the spinal structures. Schmorl nodes are prevalent even at an early age and increased thoracic kyphosis and compression fractures become evident after the age of 50 years. Therapies targeting the WNT pathway may be an effective way to prevent spinal pathology not only in those harboring a mutation but also in the general population with similar pathology.