Rare disease called rickets
Familial hypophosphatemic rickets, Vitamin D-resistant rickets
WhatX-linked hypophosphatemic rickets (XLH), also known as Familial hypophosphatemic rickets, or vitamin D-resistant rickets is a rare genetic disorder characterized by low levels of the mineral phosphorus in the blood. Unlike rickets, which occurs from a nutritional deficiency of vitamin D, XLH does not respond to vitamin D intake. Children with XLH develop leg bowing, short stature and tooth abscesses. The involved gene has recently been localized to the X chromosome.
WhoIt is estimated that one in 20, 000 children has XLH in the US. XLH is a hereditary condition. It is not contagious or preventable. XLH is an X-linked dominant condition occurring mostly in males. Women with XLH are less severely affected. Females with XLH have a 50% risk of transmitting the condition to their children. Males with XLH will transmit the disorder only to their daughters. They cannot transmit the XLH to their sons because boys receive their X chromosome from their mothers. Most affected children will have a family history of XLH symptoms. However, approximately one third of children with XLH did not receive the defective gene from their parents, instead spontaneous mutation of the gene occurred.
Signs and SymptomsInfants with XLH develop normally. Bowing of the bones does not occur until children reach walking age and begin to bear weight. While mild bowing of the legs is common in healthy toddlers and resolves with growth, in XLH the deformity continues to progress. Legs are more severely affected than arms. Children may waddle when walking or refuse to stand or walk. They may develop an exaggerated forward curvature of the lower spine to compensate for the leg bowing. Abnormal shaping of the skull may also occur. Infrequently this may cause crowding of the brain. Narrowing of the spinal canal can also develop and cause back and leg pain. Calcium deposits in tendons and ligaments can appear at various ages. Bone and joint pain are common. Short stature resulting from poor bone growth and bone deformity is a hallmark of XLH. Left untreated, adults will not grow to more than 130-165 cm (4 foot 3 inches to 5 foot 5 inches) tall. Tooth development is delayed and abscesses occur commonly due to under-mineralization of the tooth pulp, which results in expansion of the pulp and diminishes the barrier to oral bacteria. While hearing loss occurs commonly, intellectual development is usually normal. Seizures do not occur. In contrast to vitamin D-deficient rickets, in XLH, muscle weakness does not occur unless phosphate levels drop severely.
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