Skeletal abnormalities in mice with Dnmt3a missense mutations.

Area of Science:

• Genetics and Developmental Biology
• Skeletal Biology
• Molecular Endocrinology

Background:

• Tatton-Brown-Rahman Syndrome (TBRS) is an overgrowth and intellectual disability disorder.
• It is caused by mutations in the DNA methyltransferase 3A (DNMT3A) gene.
• Specific DNMT3A mutations, like R882H and P904L, correlate with varying disease severity.

Purpose of the Study:

• To characterize skeletal phenotypes in mouse models of TBRS.
• To identify cellular mechanisms underlying skeletal overgrowth in TBRS mouse models.

Main Methods:

• Generation of mouse models with Dnmt3a paralogous mutations (Dnmt3a^P900L/+ and Dnmt3a^R878H/+).
• Assessment of skeletal phenotypes in mature and juvenile mice using bone densitometry, mechanical testing, and histomorphometry.
• Analysis of growth plate chondrocytes, osteoblasts, and osteoclasts.

Main Results:

• Mutant mice exhibited tibial overgrowth, cortical bone thinning, and reduced bone mechanical properties.
• Dnmt3a^R878H/+ mutants showed increased bone marrow adipocyte size, unlike Dnmt3a^P900L/+ mutants.
• Juvenile mutants displayed thicker tibial growth plates, but no significant changes in osteoblast or osteoclast activity were observed.

Conclusions:

• Mouse models reveal novel skeletal phenotypes associated with TBRS, including tibial overgrowth and compromised bone quality.
• Findings support the clinical assessment of bone density and quality in TBRS patients.
• These results may inform the skeletal characterization of other overgrowth and intellectual disability models.