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X linked hypophosphatemia XLH is an inherited form of rickets It makes up 80 of rickets cases that have been inherited and has a rate of occurrence of 1 in 20 000 live births Jagtap et al 2012 The disorder is caused by a mutation on the phosphate regulating endopeptidase homolog x linked PHEX gene whose primary role is to create an enzyme that is most active in bones and teeth National Library of Medicine 2010 The PHEX gene does not have a direct interaction with the protein called fibroblast growth factor 23 FGF23 Jagtap et al 2012 but it is believed to be the enzyme for an intermediate protein that controls levels of FGF23 This in turn affects FGF23 s role in the reabsorption of phosphate from the kidneys leading to hypophosphatemia National Library of Medicine 2010 The pathologically low levels of phosphate leads to the softening of bones which normally contain 85 of the body s phosphate Lewis 2016 XLH is an x linked dominant disorder The mutation is found on the X sex chromosome and requires only one mutant copy to be expressed in a person Genetic and Rare Diseases Information Center GARD 2016 A female with the mutation has a 50 chance of passing the disorder on to her children regardless of sex while a male with the disorder has a 100 chance of passing the mutation to a female child and a 0 chance of passing the disorder to male children since he does not pass an X chromosome to produce a male Centre for Genetics Education 2016
