The symptoms that are listed above, as well as the obvious deformities of the extremities, anyway, there have been cases reported where people do not show any symptom of bone, and have only low levels of phosphorous in the blood. *A study conducted in 1994 by Dr. Michael Econs showed that people with mild to moderate symptoms may not be diagnosed.
If you have or have the symptoms of your children, you must go to a medical specialist (endocrinologist, nephrologist) and rule out or confirm the existence of this disease.
* Source: https://www.xlhnetwork.org/what-is-xlh/faq/