When my baby sister was two years old, she was diagnosed with a spontaneous case of X-linked hypophosphatemia (XLH). The way I usually explain it to people is that her body doesn’t absorb phosphorus and calcium correctly. This results in short stature, severe bowing of the legs, and dental abscesses. XLH has been one of the biggest parts of my family’s life for as long as I can remember, and I, as many siblings of those with rare disease can probably relate, must confess that I haven’t always been the most graceful, understanding sister in terms of my sister’s condition and everything it entails. For a long time, I was jealous and hurt by the circumstances of my sister’s disease.

As a five-year-old, it was hard to understand that my sister’s “fun” trips to Connecticut to see her doctor were not actually fun at all. The trips that I thought were full of the attention of my parents, badges from pilots on airplanes, eating at restaurants, and presents from nurses, were actually full of needles, MRIs, twelve hours of straight travel, and many tears. With the help of my parents and a newfound maturity, I later began to better grasp what the trips actually were; however, the jealousy shifted rather than faded.

My sister and I are night and day. She is loud, sassy, and demanding. Even without her rare disease, she already occupied the majority of attention from my parents, relatives, and friends. In my mind, XLH was just another thing that she had going for her. I began to resent my sister for the attention she received. Everything was always about her. But I couldn’t complain because I was healthy. I was the lucky one. I felt stuck as a young child, and sometimes even now, in a circle of guilt and jealousy.

It wasn’t until we got older that my healthy relationship with my sister’s experiences developed. I realized that I couldn’t do anything about my sister’s disease, but I could help her, my parents, and other patients. When my perspective changed, everything else followed suit. Eventually, I decided I wanted to dedicate my life to helping families like the ones that I talked to in waiting rooms and the kids my sister played with in between appointments. I plan to be a pediatric surgeon one day.

Despite my unusual childhood, I would not be the person I am without my sister’s disease. I would not be as motivated or empathetic. My goals and aspirations would be completely different. My sister and I wouldn’t be as close, and the life I grew to love wouldn’t be the same. For that I am thankful. To be honest, I wish I could give more advice, but I don’t know what advice to give or how to give it. Nobody has the same story, but I hope siblings of those with rare conditions will take comfort in knowing that they are not alone. I know I would have. The only thing I can say with confidence is that it gets better with age, perspective, and maturity. Everything gets better, and I realize now that my jealous feelings when I was younger were normal, and perhaps even healthy. My sister and I both have interesting and complex journeys, and I am glad that we get to help each other along the way.

Photograph of Marah

X-linked Hypophosphatemia (XLH)

What is it?

X-linked hypophosphatemia (XLH) is a rare, progressive, and lifelong disorder caused by low levels of phosphate in the bloodstream.

What causes it?

People with XLH produce too much of a protein called fibroblast growth factor 23 (FGF23). Too much FGF23 causes the kidneys to waste phosphate into the urine and results in chronically low levels of phosphate in the bloodstream, is also known as hypophosphatemia. Phosphate is essential for building bones and teeth.

What are some of the common symptoms?

  • Bone and joint pain
  • Bowed legs and/or knock-knees
  • Delayed growth
  • Irregular head shape
  • Muscle weakness
  • Osteomalacia
  • Short stature
  • Tooth abscesses

How many people have it?

XLH is a rare disorder, occurring in anywhere from 1 in 20,000 to 1 in 25,000, people.1

1Beck-Nielsen SS, Brock-Jacobsen B, Gram J, Brixen K, Jensen TK. Incidence and prevalence of nutritional and hereditary rickets in southern Denmark. Eur J Endocrinol. 2009; 160(3):491-497.

*These organizations are an incomplete listing of rare disease support organizations and are not controlled by, endorsed by, or affiliated with Ultragenyx Pharmaceutical Inc. The list is meant for informational purposes only and is not intended to replace your healthcare professional’s medical advice. Ask your doctor or nurse any questions you may have about your disease or treatment plan. If you would like to have your group added to the list, please contact patientadvocacy@ultragenyx.com.