Cross-sectional Evaluation Of Musculoskeletal Outcomes & Physical Activity Levels In Patients With Aggrecan Deficiency

Abstract

PURPOSE: Aggrecan is a key proteoglycan found in the extracellular matrix of articular and physeal cartilage and provides resistance to compression and deformity. Aggrecan deficiency is a recently described autosomal dominantly inherited condition due to mutations in the ACAN gene. Individuals with aggrecan deficiency experience premature growth cessation, short stature, and advanced skeletal maturation. Proteoglycan loss has been associated with osteoarthritis and degenerative joint disease. This study examines the joint manifestations of a cohort of prepubertal patients and affected family members with Aggrecan deficiency. METHODS: Probands (ACAN mutation, bone age ≥ chronological age, normal IGF-I) and affected relatives underwent baseline joint evaluation including history and physical exam, quality of life, physical activity (Marx), joint specific outcomes (Pedi-IKDC, Oswestry), and radiographic assessment (knee x-ray and MRI). RESULTS: Twenty subjects (9 male, 11 female, ages 2.4-62.6 years) were enrolled in the study. The average Pedi-IKDC of the pediatric subjects (mean age 6.5+/-3.2 years, range 2.4-12.5 years) was 95.5+/-8.9 compared to 74.9+/-20.1 for adult subjects (mean age 42.9+/-10.6 years, range 25.4-62.6 years), (p=0.02). The average Marx activity score was 12.2+/-2.2 for pediatric subjects compared to 2.6+/-4.4 for the adults (p<0.001).Two pediatric subjects reported a history of knee pain while none reported back or other musculoskeletal concerns. Additionally, two pediatric subjects were identified with osteochondral defects on MRI while 2 others displayed variant MRI findings. Of the 9 adults, 67% reported knee pain (4 patellar dislocations), 88% displayed osteoarthritis on knee x-ray, 67% reported other joint concerns, and 56% reported back pain. Seven orthopedic surgeries were reported. CONCLUSIONS: Patients with ACAN deficiency appear to be at high risk of premature joint complications as evidenced by (1) the high rate of knee, back, and joint complaints, (2) increased requirement for surgical intervention, and (3) low physical activity scores. Early surveillance of joint complaints, lifestyle counseling and therapeutic interventions to improve joint health and maintain physical activity should be considered to optimize patient outcomes and quality of life.