Mutations in WNT1 cause different forms of bone fragility

Area of Science:

• Genetics and Molecular Biology
• Skeletal Biology
• Developmental Biology

Background:

• Osteogenesis imperfecta is a congenital disorder characterized by reduced bone mass and recurrent fractures.
• WNT1 is a key signaling molecule involved in bone development and osteoblast function.

Purpose of the Study:

• To investigate the role of WNT1 gene variants in the pathogenesis of osteogenesis imperfecta and osteoporosis.
• To identify the functional consequences of WNT1 mutations on WNT signaling pathways.

Main Methods:

• Genetic analysis of consanguineous families with autosomal-recessive osteogenesis imperfecta.
• Identification and characterization of WNT1 mutations (homozygous and heterozygous).
• In vitro functional assays using osteoblasts to assess WNT1 protein activity and signaling.

Main Results:

• Five homozygous WNT1 mutations (frameshift, missense, splice-site, nonsense) were identified in families with autosomal-recessive osteogenesis imperfecta.
• A heterozygous WNT1 missense mutation was found in a family with dominantly inherited early-onset osteoporosis.
• Altered WNT1 proteins exhibited impaired activation of LRP5-mediated WNT-regulated β-catenin signaling.
• Wnt1 expression increased in osteoblasts during differentiation, highlighting its role in bone development.

Conclusions:

• Hypofunctional WNT1 alleles are causative of autosomal-recessive osteogenesis imperfecta.
• WNT1 variants, both homozygous and heterozygous, predispose individuals to low-bone-mass phenotypes.
• These findings may facilitate the development of novel therapeutic strategies for congenital bone fragility and age-related osteoporosis.