It isn't always easy to find a health care provider for treatment of a rare disorder, and yet, it's absolutely critical for these patients to see a specialist who has the most up-to-date information on appropriate treatment and the potential side effects, and who also has access to information on clinical trials.
So, how do you find such a specialist? The first step is to ask the XLH Network community. If you're a member of the Network, you have access to our database of health care providers who have been recommended by other patients. You can find a link to join at our website: XLHNetwork.org
If our database doesn't have a specialist who's local to you, then you have two options: 1) you can travel to a city that has well-known experts—highly, highly recommended for pediatric treatment—which our members will tell you about at our online community, or 2) look for someone local who has the necessary expertise.
If you're going to find your own local expert, your best bet is usually at a teaching hospital. For an online search tool for teaching hospitals in the United States, check out Health Guide USA here: http://www.healthguideusa.org/teaching_hospitals.htm
Once you've located the teaching hospital in your area, you still need to find an individual doctor. Most hospitals today have websites where you can search for doctors based on their medical specialty. For the day-to-day treatment of XLH (as opposed to something like surgical intervention or pain management), the relevant specialty is endocrinology. That specialty covers a broad range of conditions, though, so look for someone who mentions an interest in "bone metabolism."
It would be nice if you could interview the doctor before your first appointment, but that's not generally possible in the United States. Still, your work is not finished until you've actually met the specialist and confirmed that he/she is right for you. Remember that you don't have to keep the first doctor you see, so be prepared to ask a few questions about his/her expertise during the first appointment. The doctor obviously can't share any personal information about his/her patients but should be able to say how many XLH patients he's treated and what other relevant experience he has with bone metabolism issues.
It can take some time to find the right doctor, but, particularly for a rare condition, where improper treatment can be extremely harmful, it's worth the extra effort to work with someone who is familiar with the disorder and its treatment.