September 2026 Research Update

This month, real-world studies added a clearer picture that burosumab (an anti-FGF23 antibody) is consistently linked with improved phosphate-related lab results, and that some everyday-impact measures can improve over time, especially in adults. What became clearer is that lab and bone-imaging changes may line up strongly with each other in children, while links to height, quality of life, or motor function were weaker or not seen in these datasets. [1] [2] [3]

In adults followed for 3 years in routine care, burosumab was compared with oral phosphate plus active vitamin D (Pi/D). After adjusting for starting differences between groups, people receiving burosumab had larger increases in blood phosphate and a higher share reached at least the lower end of the normal phosphate range, and by year 3 they also reported better pain, stiffness, and physical function scores on a standardized arthritis-style questionnaire. [1]

In Japanese children in the SUNFLOWER program, 1 year of burosumab was linked with improved phosphate-related labs, and changes in rickets severity on x-rays moved closely with changes in alkaline phosphatase (a blood marker related to bone turnover). In that same analysis, changes in height did not show a clear relationship to alkaline phosphatase changes, and changes in lab markers did not clearly track with reported quality of life or motor function measures. [2]

A separate German-Swiss study focusing on children and teens already receiving burosumab found that many self-reported quality of life scores were similar to, or slightly higher than, general population reference values, while parent or caregiver reports were lower for physical well-being and autonomy. Within this treated group, burosumab dose was reported as an independent predictor of several quality of life areas, including physical well-being. [3]

For families living with XLH, these studies mainly add context about what changes tend to move together during burosumab treatment in real-world care, rather than proving what will happen for any one person. The adult follow-up suggests that improvements in blood phosphate may be accompanied by better day-to-day symptom scores over longer periods, while the pediatric data suggest that a simple blood marker (alkaline phosphatase) may help reflect changes seen on rickets imaging. What remains uncertain is how strongly these lab and imaging changes predict practical outcomes like stamina, school participation, or height in the short term, because those links were not clear in the 1-year pediatric analysis and quality of life measures varied by who reported them. This information may matter now for understanding what different tests and questionnaires are capturing, and it may matter more later if larger studies confirm which measures best reflect meaningful daily improvements. [1] [2] [3]

This month brought a broader, health-system view showing that when people with rare bone diseases are hospitalized, their hospital courses tend to be more complicated than similar hospitalizations in the general population. For XLH specifically, the study highlighted a pattern of more emergency admissions in late adulthood and a notable presence of malignancy diagnoses among hospitalized patients with XLH. [4]

Using national hospitalization data from 2012 to 2021, the study compared admissions involving six rare bone diseases with matched admissions from the general population. Across the rare bone disease group, hospital stays were longer and ICU admissions and readmissions were more common, and the report also found higher in-hospital mortality during these admissions. [4]

Within the XLH subgroup, the analysis reported an increased risk of emergency admissions in late adulthood, and malignancies were diagnosed in 22.7% of hospitalized patients with XLH. The study did not explain why malignancies appeared in this hospitalized XLH group, so it cannot tell from this dataset whether XLH itself, treatments, age, or other health factors were driving that pattern. [4]

For patients and caregivers, this study adds perspective that hospitalizations involving rare bone diseases, a group that includes XLH, may come with higher complexity than typical admissions, which can help explain why hospital stays or readmissions might happen more often in this population. The malignancy finding is best read as a description of what was recorded among hospitalized XLH patients in this dataset, not as a personal prediction for someone living with XLH. What remains uncertain is what types of malignancies were included and what factors contributed to these diagnoses, because the summary results did not provide that level of detail. This information may matter now mainly for understanding the broader health burden seen in national hospital data, and it may guide future research on which complications lead to hospital care in XLH. [4]

This month, smaller and more specialized reports added nuance to diagnosis and monitoring rather than showing new treatment outcomes. The main message is that getting the diagnosis exactly right can require the right genetic testing approach, dental issues are recognized as part of rare-disease care pathways, and one very small study did not find a clear blood or urine hormone signal explaining heart muscle size differences in young people with XLH. [5] [6] [7] [8]

Two case reports showed how genetic findings can complicate or clarify an XLH diagnosis. One child had a noncoding (intronic) PHEX variant that was missed on clinical exome sequencing but found on a targeted gene panel, with computer predictions suggesting the change disrupts splicing and a possible mosaic pattern. [5]

The other case report described a person with a PHEX deletion who also carried two pathogenic SLC34A3 variants (confirmed to be on the same chromosome using long-read sequencing), raising a diagnostic and treatment dilemma because SLC34A3 is tied to a different phosphate-wasting condition. The report emphasized reviewing broader genetic results when lab patterns do not look like classic XLH. [6]

Dental care also appeared in this month’s literature through an English-language summary of a German guideline on rare dental disorders. It described 41 recommendations across diagnosis and different types of dental treatment, and it placed XLH among conditions where multidisciplinary care and genetic testing can be important for planning. [7]

In early biologic research, a pilot study of 7 young people with XLH measured angiotensin-related hormones in blood and urine and compared them with echocardiogram measurements of heart muscle size. The study did not find significant correlations overall, which argues against these hormone levels being an obvious explanation for left ventricular mass differences in this small group. [8]

For patients and caregivers, these reports mainly matter as reminders of what can make XLH diagnosis and long-term monitoring more complicated. The case reports show that some PHEX changes may be missed depending on the test used, and that additional variants in other phosphate-related genes can muddy the picture when lab results do not match expectations; this is early, individual-level evidence and may not apply widely. The dental guideline summary does not report new study results, but it signals that oral and dental needs are being treated as a standard part of rare disease planning in some health systems, although the guideline itself notes that evidence quality can be limited. The heart-hormone study is very small and does not change what is known about heart health in XLH, but it helps narrow down which biologic pathways may be less likely to explain heart muscle findings and points to the need for larger follow-up research. [5] [6] [7] [8]