It sometimes feels like the XLH community has a foot in each of two universes — one that’s moving forward with a life-changing treatment, and one that’s stuck in the past. And, really, the XLH community split into almost two different disorders in 2018 when burosumab started to become commercially available—one that consisted of patients born from that year forward and (at least potentially) had access to burosumab pretty much from birth, and the patients born before then who didn’t have effective treatment. Those of us with advanced and irreversible symptoms in 2018 saw benefits from treatment, but the real difference has yet to be completely known, as kids grow up on burosumab, essentially never (or only very briefly) having experienced life with low phosphorus levels.
Back when I spearheaded the creation of Weak Bones, Strong Wills, one of the goals was to document the experiences and challenges of XLH patients and caregivers BEFORE there was an effective treatment, and the untreated lived experience disappeared. It’s disheartening to see that, in a sense, there was no need to document it, because too many patients continue to get ineffective treatment (if any).
You can see these two universes (before and after burosumab) laid out pretty starkly by looking at a pair of journal articles published within a few days of each other, one showing the truly life-changing effects of burosumab for kids, and one showing how poorly the old treatment worked on kids in the past, and presumably now for the kids who have no other options.
The first (future-facing) article, published in a reputable journal on June 13, is “Switching From Active Vitamin D and Phosphate Supplementation to Burosumab Significantly Corrects Lower Limb Malalignment in Pediatric XLH.” Conclusion: “This study shows that switching to burosumab significantly improves lower limb malalignment in children with XLH over benefits conferred by [old phosphorus and calcitriol treatment], with early burosumab initiation providing the greatest benefit.” In other words, from the patient’s point of view: all kids should be on the new treatment, starting as soon as they’re diagnosed!
The second article, published three days earlier in another reputable journal is “Growth dynamics of transversal body dimensions and proportions, with related clinical determinants in children with X-linked hypophosphatemia treated with phosphate supplements and active vitamin D.” The science is a bit dense, but to this non-doctor, non-statistician, it looks both solid (data going back farther than most XLH studies do, to 1998) and potentially useful (new insights into how our bones are stunted), but also moot for patients who are on the more effective new treatment, which, unlike the only treatment available for the bulk of this study, vastly improves the stunting and whatever else is going wrong with our bones.
The science in this article is a bit beyond me, but it seems to be saying, once again, that the old phos/calcitriol treatment isn’t particularly effective. Conclusion: “Our data show disproportionate growth in transversal [width-wise] body dimensions despite supplementation treatment in children with XLH, suggesting compensatory widening of tubular bones as adaptation for mineral loss caused by persisting rickets.”
I do find this second article interesting from a theoretical perspective, rather than a practical usefulness perspective. It seems to be the first study that has paid attention to the WIDTH of our bones, not just the length of them. Anecdotally, I’ve seen a lot of XLHers who appear to have large bones (horizontally and around), just not long ones. I’ve always described myself as being a tall person whose bones were squashed, so the total amount of bone is the same as if I were as tall as my mother (5′ 9″), just in a package that’s wider and shorter than it would have been with adequate phosphorus. And that extra mass is good, if patients need surgery, since (assuming the bones have been treated properly before surgery to maximize their mineralization) larger bones give the orthopedic surgeon more material to work with.
So, ultimately, even though some of the results are moot due to changing treatment, the past-focused article is still enlightening, and has some applicability to both subgroups of the community. Among other things, it’s a good reminder to health care providers that the length of bones is not the only thing that matters to patients. I think a lot of clinicians assume that XLHers must be at high risk for osteoporosis, because they’re equating “short” with “small,” so they conclude we must have small bones, which, for at least some of us, is simply not true. Many of us have short but large (or larger than expected based on length) bones. And some of us (raises hand!) have tons of calcium in and around our bones, but it’s not a sign of health bones, and instead is a problem, since the extra calcium is in our soft tissues instead of our bones. I sometimes wish there were a way to get the calcium-leaching process that causes osteoporosis to refocus and turn its powers on our calcified soft tissue and leach the unwanted calcium from where it doesn’t belong. Unfortunately, from what I’ve read, science doesn’t know enough about the soft-tissue-calcification process to be able to even hypothesize a method for reversing it. Maybe someday!
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Please note that the author is a well-read patient, not a doctor, and is not offering medical or legal advice.
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