Low bone turnover phenotype in Rett syndrome: results of biochemical bone marker analysis

Background: Patients with Rett syndrome (RTT) are at risk of having low bone mass and low-energy fractures. Methods: We characterized bone metabolism by both bone formation and resorption markers in blood in a RTT population of 61 girls and women and 122 well-matched healthy controls. Levels of N-terminal propeptides of collagen type 1 (P1NP), C-terminal telopeptide cross links (CTX), osteocalcin (OC), and bone-specific alkaline phosphatase (B-ALP) were compared between RTT patients and controls in regression models adjusted for BMI, vitamin D status, volumetric bone mineral apparent density of the lumbar spine (vBMAD spine ), and femoral neck (vBMAD neck ). We examined biochemical bone marker levels overall and stratified to persons younger than age 25 y or equal to or older than age 25 y. Results: The RTT patients had reduced levels of all biochemical bone markers ( P < 0.05), which remained significant in persons younger than 25 y ( P ≤ 0.001) regarding P1NP, CTX, and OC. Bone marker levels were not significantly associated to methyl-CpG-binding protein 2 ( MECP2 ) mutation group, walking ability, or previous low-energy fractures. Conclusion: Our findings of a low bone turnover state in girls with RTT suggest critical attention to medical treatment of low bone mass in young RTT patients.