Suitability of growth standards for growth monitoring in children with genetic diseases

Growth references are used worldwide. The objective of monitoring growth of apparently healthy children is to identify treatable diseases early. Children with compromised growth, e. g. due to genetic disease, are assessed and compared to common growth references based on healthy children. But children with genetic diseases often fulfil the most referral criteria for further evaluation already due to their underlying disease. So, only the height deflection criteria (excessive decrease in height Z-score over time) seem reasonable in these children. But it is unclear whether one should expect these children to follow the standard growth references. The aim of the study was to develop a tool for evaluating the applicability of common growth standards for growth monitoring of children with specific genetic disease. We introduced the percentile parallelism test (PPT). This novel test assesses whether a height deflection is to be expected due to the underlying specific genetic disease, or if it is a sign of an additional disease. For illustration, the PPT was applied to a cohort of boys (n = 28, age 2-16 years) with osteogenesis imperfecta type IV. Boys with osteogenesis imperfecta showed a significant (p = 0.001) higher variability of their age specific height distribution than their healthy peers. Therefore, the commonly proposed cutoffs for the height deflection criteria had to be adjusted by the factor of 1.342 (95% CI 1.337-1.347). The PPT might improve the growth monitoring of children with genetic diseases, preventing them from unnecessary diagnostics.