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X-linked hypophosphatemia

X-linked hypophosphatemia. Tom Gillespie Rinzin Dorjee Martin Kutti. X-linked dominant hypophosphatemic rickets, X-linked vitamin d-resistant rickets or hypophosphatemic vitamin d-resistant rickets (HPDR ).

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X-linked hypophosphatemia

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  1. X-linked hypophosphatemia Tom Gillespie Rinzin Dorjee Martin Kutti

  2. X-linked dominant hypophosphatemic rickets, X-linked vitamin d-resistant rickets or hypophosphatemic vitamin d-resistant rickets (HPDR) • X-linked dominant form of rickets (or osteomalacia) that differs from most cases of rickets in that ingestion of vitamin D is relatively ineffective. It can cause bone deformity including short stature and genu varum (bow leggedness). • Marked by bone distortions, nodular enlargements on the ends and sides of the bone, delayed closure of the fontanelles, muscle pain etc. • associated with a mutation in the PHEX gene sequence (Xp.22) and subsequent inactivity of the PHEX protein. • The prevalence of the disease is 1:20000

  3. Infected Children

  4. Causes and Genetics • XLH is associated with a mutation in the PHEX gene sequence, located on the human X chromosome at location Xp22.2-p22.1 • The mutation results in altered (or missing) activity of the PHEX protein, which inactivates hormone-like substances (phosphatonins) that promote phosphate excretion. • The resulting excess excretion of phosphate impairs bone mineralization • Biochemically, XLH is recognized by hypophosphatemia and inappropriately low level of calcitriol • The disorder is inherited in an X-linked dominant manner.

  5. The defective gene responsible for the disorder (PHEX) is located on the X chromosome, and only one copy of the defective gene is sufficient to cause the disorder when inherited from a parent who has the disorder. • Males - homozygous for the X chromosome, having only one copy. As a result, X-linked dominant disorders usually show higher expressivity in males than females. • As the X chromosome is one of the sex chromosomes (the other being the Y chromosome), X-linked inheritance is determined by the gender of the parent carrying a specific gene and can often seem complex. • This is due to the fact that, typically, females have two copies of the X-chromosome, while males have only one copy. • The difference between dominant and recessive inheritance patterns also plays a role in determining the chances of a child inheriting an X-linked disorder from their parentage.

  6. X-linked dominant inheritance works differently depending upon whether the mother (left image) or father (right image) is the carrier of a gene that causes a disease or disorder

  7. References • 1. Online 'Mendelian Inheritance in Man' (OMIM) 307800 • 2. "Familial hypophosphatemic rickets caused by a large deletion in PHEX gene". European Journal of Endocrinology 161 (4): 647–651. • 3. Carpenter TO (Apr 1997). "New perspectives on the biology and treatment of X-linked hypophosphatemic rickets".

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