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298X 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
It is possible however for the PHEX gene to be a de novo mutation GARD 2016 While the mutation is not distinct to any particular ethnicity Jagtap et al identify it as the most common form of refractory rickets in Indian children 2012 The first physical assessment usually identified is irregular growth of the skull GARD 2016 in the form of frontal bossing generally around the age of 6 months Jagtap et al 2012 as well as possible craniosynostosis Ruppe 2012 When the child begins weight bearing long bone deformities in the form of bowed legs become apparent Ruppe 2012 The condition results in short stature Pettifor 2008 Bone and joint pain are later clinical manifestations GARD 2016 and persons with XLH are prone to dental abscesses because of demineralization of tooth dentin Ruppe 2012 There have been some rare cases of hearing loss reported GARD 2016 Untreated XLH can lead to osteomalacia Carpenter Holm et al 2011 Within families the severity of the condition and its clinical manifestations can vary Jagtap et al 2012 It is believed that the more severe the PHEX mutation within a person with X linked hypophosphatemia the stronger the expressivity of the condition Morey et al 2011 This is especially likely since those with deleterious mutations appeared to have lower tubular reabsorption of phosphate Morey et al 2011
The nurse should stress the importance of excellent oral hygiene and the importance of early dental intervention to mitigate the frequency and severity of dental abscesses Ruppe 2012 It is suggested that X linked hypophosphotemia should be suspected in children with leg bowing after the beginning of ambulation along with radiographic findings such as widening at the growth plates of the long bones Ruppe 2012 The diagnosis is confirmed by a low serum phosphate the tubular reabsorption rate of phosphate and an inappropriate level of calcitriol Ruppe 2012 Genetic confirmation is when the PHEX mutation is found in a hemizygous male or heterozygous female Ruppe 2012 Dr Ruppe writes that in families where the pathogenic PHEX gene has been identified it can be beneficial for infants to be tested for the mutation in order to begin early intervention to have optimal long term results 2012 The majority of probands with X linked hypophosphotemia can be identified by sequence analysis Ruppe 2012 Prenatal testing and preimplantation genetic diagnosis is available for affected persons These tests present both patients and medical professionals with possible ethical dilemmas as these conversations can be for early diagnosis but can also be regarding possible termination of pregnancy Ruppe 2012 While X linked hypophosphatemia can lead to life long deformities and pain if left untreated it is a condition that if detected early and managed appropriately can still allow persons especially those with low expressivity to have a relatively normal quality of life
