Bone Age Delay in X-linked Hypophosphatemia

Bone age (BA) assessment and prediction of adult height (AdHt) has not been well studied in children with X-linked hypophosphatemia (XLH).

To assess BA and its utility in height prediction in children with XLH.

Retrospective, cross-sectional, and longitudinal assessments of BA using 2 standard methods in children with XLH. Mean values were used to calculate predicted adult height (PAH), which was compared to final or near-final AdHt in patients who were at or near the end of growth.

Academic medical center.

Fifty-six children with XLH.

None.

BA, PAH.

Initial radiographs demonstrated BA delay (chronologic age-BA) of 1.2 ± 1.0 (mean ± SD) years in males and 0.4 ± 1.0 years in females (greater delay in males, P < .05). Fifty-eight percent of males and 21% of females were delayed 1 to 2 years; 11% of males and 9% of females were delayed more than 2 years. For 4 males with no prior orthopedic surgeries, mean AdHt was 171.2 ± 5.3 cm; PAH was 176.3 (±11.7) cm using Bayley-Pinneau methods and 173.0 ± 6.8 cm per Tanner-Whitehouse methods. For 15 females without prior orthopedic surgeries, AdHt was 155.9 ± 5.2 cm; PAH was 156.0 ± 6.8 cm (Bayley-Pinneau) or 161.6 ± 4.2 (Tanner-Whitehouse, which differed from AdHt, P < .005).

BA is delayed in children with XLH but more strikingly so in males. Height predictions were within a range typically used in healthy children (±2 inches). The Bayley-Pinneau method appears to modestly overestimate AdHt in males, whereas Tanner-Whitehouse overestimates AdHt in females.