March 2026 Research Update

Studies this month added more detail on what burosumab (a medicine that blocks FGF23) looks like in everyday use for X-linked hypophosphatemia (XLH), and how monitoring might work in real life. A large real-world analysis in children linked burosumab use with faster growth over time compared with children not on burosumab. A smaller substudy suggested that blood phosphate and calcium results on burosumab were similar whether drawn fasting or after meals, which could matter for making blood testing easier when fasting is difficult. [1] [2]

In the real-world APEX analysis, burosumab-treated children and adolescents had higher growth velocity than burosumab-naive participants, and the researchers' modeling predicted greater adult height for treated patients. This does not prove the medicine caused the growth differences, because children were not randomly assigned in this analysis, but it strengthens the picture that burosumab use is linked with improved growth patterns in routine care settings. [1]

In the meal-timing substudy nested within phase 3 trials, serum phosphorus levels after breakfast or lunch were not meaningfully different from fasting levels in both children and adults receiving burosumab, and calcium stayed largely within the normal range. In plain language, this suggests that non-fasting blood draws may often give similar information to fasting draws for these two lab values, at least in the stable trial participants who were studied. [2]

For families thinking about growth and day-to-day management, this month mainly adds practical context rather than changing what is known overnight. The growth findings may matter now as supporting evidence that, in routine care, children on burosumab can show faster growth than those not on it, although the study design cannot fully separate treatment effects from other differences between groups. The meal-timing results may matter now for the logistics of blood testing, because they suggest phosphate and calcium checks on burosumab may often be interpretable even if fasting is not possible, but this was based on a small group from clinical trials and results could vary between people. [1] [2]

This month included one study focused on dental and jaw features in XLH, asking whether conventional treatment with oral phosphate plus active vitamin D meaningfully improves tooth-related mineral problems. The results were mixed: in the Hyp mouse model, the treatment did not meaningfully restore several measured tooth and gum-support features, while small human tooth samples showed thicker predentin (a softer layer before it hardens) and some signs of better dentin mineralization, especially when treatment adherence was good. Taken together, the study supports the idea that tooth mineralization problems in XLH may be difficult to fully correct, even when blood phosphate is treated. [3]

In mice treated from 3 weeks of age, phosphate plus active vitamin D did not significantly improve dentin and cementum measures or periodontal attachment compared with untreated Hyp mice. In the human tooth samples, treated XLH teeth had increased predentin thickness compared with non-XLH control teeth, but some abnormal areas in dentin still persisted. [3]

This study mainly matters as early research about why dental issues can remain part of XLH, even with long-term medical treatment. It suggests that some tooth layers may show partial improvement with conventional therapy, but it also highlights that deeper mineralization changes may not fully normalize. What remains uncertain is how well these small tissue findings predict everyday dental outcomes for most people with XLH, because the human sample size was very small and the mouse results may not fully match human tooth development. [3]

Case reports this month described how XLH-related complications may be managed in highly individualized ways, especially when bone healing is slow or when long-standing disease has led to complex problems. Across these reports, patients improved in specific goals such as head shape after skull surgery or walking ability after limb deformity correction, but the reports also emphasized that responses and risks can vary a lot from person to person. Because each report is a single patient, these stories are best read as examples of what is possible rather than predictions of what will happen for others. [4] [5] [6]

One report described fronto-orbital distraction (a technique that gradually expands skull bones) for craniosynostosis in a patient with X-linked hypophosphatemic rickets. Bone formation was slower than expected, but the skull still expanded and the final head shape was described as favorable, with no major adverse events reported. [4]

Another report described a teenager with XLH diagnosed by genetic testing who had lower-limb deformities corrected using the Ilizarov technique with multi-segment osteotomy. After surgery, he could walk independently and care for himself, and no complications were reported. [5]

A third report described an adult woman with XLH who also carried a CLDN16 gene variant and had kidney calcification and severe secondary hyperparathyroidism after long-term phosphate therapy. After subtotal parathyroidectomy and later burosumab, the report described partial improvement in lab values and meaningful improvement in pain and mobility, with no serious adverse effects reported; the role of the CLDN16 variant remained uncertain. [6]

For patients and caregivers, these single-person reports mainly add real-world examples of how varied XLH can be, including skull, limb, and kidney-related complications. They may matter later by helping researchers and care teams recognize practical issues such as slower bone formation after craniofacial surgery or the possibility of complex kidney and parathyroid problems after long-term conventional therapy. What remains uncertain is how often these situations occur and how reliably the same approaches work in others, because case reports cannot separate what is typical from what is unique to one person. [4] [5] [6]