Final answer:
Hypophosphatemic rickets is caused by genetic factors affecting phosphate transport and regulation, leading to hypophosphatemia and bone deformities. An X-linked dominant pattern controls the inheritance of this condition, where affected females have a 50 percent chance of passing it to their children, while affected males will transmit it to all their daughters. Vitamin D plays a crucial role in the disease, with deficiencies resulting in the characteristic bone malformations.
Step-by-step explanation:
The causes of hypophosphatemic rickets relate to genetic and phenotypic factors. Genotypically, it may arise due to mutations affecting phosphate regulation in the body, including defective transport of phosphate by the intestine and the renal tubules. This leads to lowered serum phosphorus, a condition known as hypophosphatemia, and hyperphosphaturia. Phenotypically, individuals with hypophosphatemic rickets often present with brittle bones that fracture easily, pain from vertebral fractures, and bone deformities due to defective bone mineralization.
One variant of hypophosphatemic rickets is X-linked dominant, meaning the abnormal gene responsible is located on the X chromosome. For example, a male with this form of the disorder would pass it on to all of his daughters but none of his sons, as males only pass on the Y chromosome to male offspring. An affected female has a 50 percent chance of passing the disorder on to each child, regardless of sex. The phenotype of individuals with hypophosphatemic rickets can include appendicular skeleton deformities and problems with phosphate homeostasis.
The role of vitamin D in rickets is crucial, as it helps with the absorption of calcium and phosphate. A deficiency in vitamin D can result in rickets, with symptoms like low serum phosphorus (P) levels and increased alkaline phosphatase activity, which are characteristic of the disease. This type of rickets is resistant to vitamin D, leading to the term 'vitamin D-resistant rickets.' Like other rickets, it is characterized by bone deformities due to inadequate bone mineralization.