ESPE Yearbook of Paediatric Endocrinology

J Clin Endocrinol Metab. 2020 Oct 1;105(10):3243–3249 Abstract: https://pubmed.ncbi.nlm.nih.gov/32721016/

In brief: X-linked hypophosphatemia (XLH) is the most common hereditary form of rickets and osteomalacia. The study used retrospective, pre-burosumab growth data from four different studies and constructed growth charts that demonstrate that the growth rate of children with XLH clearly becomes subnormal at approximately 1 year of age.

Comment: To better characterize growth impairment in patients with XLH, retrospective growth data collected in the observational study UX023-CL002 and pre-treatment data from the 3 pediatric clinical trials UX023-CL201, -CL205, and -CL301 were used to construct growth curves for children with XLH, a large majority of whom were receiving conventional therapy with phosphate supplements and active vitamin D. The annual height increment in children with XLH deviated from that of healthy children starting at age 6 months. For boys, median height percentiles were 46% at 3 months, 37% at 6 months, 18% at 1 year, and 5% at 2 years of age. Similar declines were observed in girls: 52% at 3 months, 37% at 6 months, 18% at 1 year, and 7% at 2 years of age.

These findings confirm previously published smaller data sets assessing linear growth in children with XLH that have showed a distinct decline in height z-scores/percentiles after 1 year of age due to rapid growth deceleration that may occur as early as age 9 months. These findings are also consistent with previous studies suggesting that early start of treatment is important result in improved outcomes in terms of height and deformities (1). These disease-specific growth charts for boys and girls will be very useful tools in the monitoring general health as well as the effects of medical treatments in children with XLH.

Reference: 1. Makitie, O., et al., Early treatment improves growth and biochemical and radiographic outcome in X-linked hypophosphatemic rickets. J Clin Endocrinol Metab, 2003. 88(8): p. 3591–7.