I mostly bring you chronic hypophosphatemia research that’s fairly broadly applicable to our community, but this week I have some resources that may be useful for sub-groups of our community.
ENPP1 Deficiency. The first is some natural-history-type data on chronic hypophosphatemia patients whose symptoms are caused by ENPP1 deficiency. You may not recognize that label, but may have heard of Global Arterial Calcification in Infancy (GACI), which was considered related to the XLH community until the ENPP1 gene was discovered as the cause for their hypophosphatemia. I still consider these patients to be our cousins, since the ones who survive infancy generally develop chronic hypophosphatemia and all the same symptoms an XLHer experiences, even if they have a different genetic mutation.
In any event, there’s a new article, “Phenotypic characterization of ENPP1 deficiency,” that suggests that the understanding of these patients is progressing much the way the understanding of XLH has, from initially thinking there was just one symptom (rickets for us, cardiovascular calcification for ENPP1 patients) to realizing that the conditions are both, in fact, whole-body, whole-life, whole-family disorders. The abstract notes the commonly known musculo-skeletal symptoms for ENPP1 deficiency, and then adds, “The clinical picture … in this study extended beyond skeletal deformities to include hearing impairment, joint involvement, and ongoing risk of cardiovascular problems.”
I find it particularly interesting that, just as with XLH, hearing impairment has been added to the list of ENPP1 symptoms. I’ve mentioned before that a doctor at Massachusetts Eye & Ear Infirmary is studying Meniere’s (a form of hearing loss and vertigo) in a small number of XLH patients. I’m hopeful that a future phase of the research will look into other hearing issues and include more patients, including perhaps some of the other hypophosphatemias, like TIO and ENPP1. I have to wonder if the similarities and differences across the various subcategories of hypophosphatemia might lead to better understanding of hearing loss for all of us.
Craniosynostosis. The second article is “Craniosynostosis among children with X-linked hypophosphatemia.” This article is specific to XLH, but the condition it covers fortunately only occurs in a relatively small percentage of our community. Craniosynostosis is a skull abnormality, treated with surgery. I knew it was more common among XLHers than the general population, but not how much more common. According to this article, it occurs in 22% of XLHers, and only .05% (note the decimal places!) of the general population. And if I read it right (I only have access to the abstract, not the full article), it’s more commonly seen in boys than in girls, even though there are more girls with XLH than boys. Which of course isn’t to say that XLH girls can’t experience it — the one real-life patient I know who had craniosynostosis (and successful surgery to treat it) is a girl!
There’s another article about craniosynostosis published recently, “Significance of assessing the severity of craniosynostosis in patients with X-linked hypophosphatemia (XLH) at diagnosis,” but I don’t even have access to an abstract. I’m just noting it here for future reference, in case it’s useful for a parent to share with a clinician who could access the journal where it’s published (Clinical Pediatric Endocrinology).
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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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