Biomarkers Related to Bone in Pediatric Gaucher Disease

Gaucher disease (GD), the most common lysosomal storage disorder, is caused by a deficiency of the enzyme glucocerebrosidase. Clinically, there are three sub-types according to neurological involvement. Type 1 GD (GD1) is non-neuronopathic GD, and GD types 2 and 3 (GD2-3) are neuronopathic forms. Bone involvement includes skeletal structural abnormalities such as Erlenmeyer flask deformities, cystic changes, growth retardation, progressive kyphoscoliosis, osteonecrosis, bone density abnormalities, bone fragility, and pathological fractures occur at a spectrum in different GD clinical types. While bone crises are rare (often referred to as Gaucher crises), avascular necrosis (AVN) may occur in the pediatric age group with long-term morbidity and is often associated with chronic pain and orthopedic deformities requiring multiple surgical interventions. As known, the development of the skeleton development (longitudinal and bone mass growth) is subject to both environmental and genetic influences. During childhood, skeletal growth is characterized by rapid bone growth and continues to lengthen bones by adding bone tissue on the epiphyseal plate until adolescence. The thickening of long bones is processed by adding bony tissue to its surface. The process of bone remodeling and repair continues after birth and adulthood. Bone marrow infiltration and bone remodeling defects termed "Erlenmeyer flask deformity" are the most common GD-related bone diseases. Without intervention directed at GD, bone involvement usually starts before puberty. Moreover, children with severe GD present retarded growth and delayed puberty (\<5th percentile in 34% of children). However, the underlying mechanisms of regulation of bone development and related complications in the pediatric age group in GD are not yet fully known. Neither the bone-specific biomarkers nor their relationship regarding growth factors associated with normal bone turnover during the normal growth process have been studied in detail in GD in the pediatric age group. Abnormalities in skeletal growth and bone turnover may be related to the abnormal regulation of some growth factors, for example, the elevation of fibroblast growth factor 23 (FGF23) or inhibition of insulin-like growth factors (IGFs) resulting in bone growth impartment. Moreover, chronic inflammation leads to alterations in the function and differentiation of osteoclasts and osteoblasts, which participate in bone growth and remodeling. Furthermore, the evaluation of bone involvement could be challenging for the pediatric age group. The marrow replacement due to GD that moves in the opposite direction with the expected disappearance of the red marrow makes it challenging to evaluate the bone marrow using MRI and requires experience and technical skills to interpret the imaging studies. In addition, the technique of bone density evaluation is still not uniform in children, especially for different age groups.