Inherited vitamin D disorders

• What is Inherited Vitamin D Disorders
• Statistics on Inherited Vitamin D Disorders
• Risk Factors for Inherited Vitamin D Disorders
• Progression of Inherited Vitamin D Disorders
• Symptoms of Inherited Vitamin D Disorders
• Clinical Examination of Inherited Vitamin D Disorders
• How is Inherited Vitamin D Disorders Diagnosed?
• Prognosis of Inherited Vitamin D Disorders
• How is Inherited Vitamin D Disorders Treated?
• Inherited Vitamin D Disorders References

What is Inherited Vitamin D Disorders

Inherited Vitamin D Disorders affect the kidneys.

Namely the renal tubules. There are three forms of inherited Vitamin D disorder. These include vitamin D-resistant rickets, Type I vitamin D-dependent rickets and Type II vitamin D-dependent rickets.

Statistics on Inherited Vitamin D Disorders

These are rare inherited conditions which arise from inherited defects in renal enzymes. These enzymes are normally active and present in the kidneys, but when defective, lead to poor metabolism of vitamin D and minerals such as phosphate and calcium, giving rise to the disease state of rickets. These conditions occur in childhood, where the deformities develop, which are carried into adulthood.

Risk Factors for Inherited Vitamin D Disorders

As the condition is invariably inherited, a family history of the condition is the only predisposing factor.

Progression of Inherited Vitamin D Disorders

As the condition is inherited, the primary defect will be present at birth and the disease process will begin in the first stages of life. Children will typically be growth retarded and experience bowing of the legs on commencement of walking.

In X-linked hypophosphatemic rickets, the deficiency on growth will be almost exclusively restricted to the lower limbs. Delaying teeching and skull abnormalities will be present at an early age with bowing of the legs occurring as the child begins to walk. Growth deficiency will be permanent on reaching adulthood if no intervention is undertaken. Overgrowth of bones at muscle and joint origins may lead to pain, immobility and nerve entrapment in later life.

Type I Vitamin D-dependent rickets follows a similar natural history to that of X-linked hypophosphatemic rickets. It is inherited in a recessive manner.

Type II Vitamin D-dependent rickets occurs with end-organ resistance to activated Vitamin D (1,25(OH) Vit D). It is also inherited in a recessive manner, however cases have been reported without a family history. Most will present in childhood, but milder forms of the disease occur that are not recognised until adulthood. The severe form of this condition condition is hallmarked by baldness in childhood which persists into adulthood.

How is Inherited Vitamin D Disorders Diagnosed?

A number of blood tests will be required to differentiate the type of inherited defect. Levels of calcium, phosphate and vitamin D are all important to the diagnostic process.

Prognosis of Inherited Vitamin D Disorders

X-linked Hypophosphatemic Rickets:

With appropriate therapy, patients will experience improved growth and development. These patients require close monitoring due to the increased risk of calcium deposition and reduced renal function in this condition.

Type I Vitamin D-dependent Rickets:

Excellent prognosis with appropriate therapy, leading to cmplete resolution of bone disease.

Type II Vitamin D-dependent Rickets:

The prognosis is fair, as the response to therapy is variable. The extent of bone disease will be improved with multiple medications but some patients may not respond well to treatment.

How is Inherited Vitamin D Disorders Treated?

All of these inherited conditions cannot be cured, and require life-long supplementation of vitamins and minerals to maintain growth and reduce the risk of complications such as deformity and renal failure.

1. X-linked hypophosphatemic rickets: The main aim is to correct the low phosphate level. The mainstay of treatment includes oral phosphate supplementation 4-6 times daily with calcitriol. These patients have an increased tendency to calcium deposits in the kidney and renal failure, and therefore require regular disease surveillance

2. Type I Vitamin D-dependent rickets: This condition can be effectively managed solely with calcitriol, correcting both biochemical abnormality and skeletal manifestations of disease.

3. Type II Vitamin D-dependent rickets: This condition is treated primarily with calcitriol, however large doses may be required to achieve any appreciable effect in severe cases. Mineral supplements of calcium and phosphorus may also be useful but should be considered as a adjunct to calcitriol therapy.

Inherited Vitamin D Disorders References

[1] Braunwald, Fauci, Kasper, Hauser, Longo, Jameson. Harrison’s Principles of Internal Medicine. 15th Edition. McGraw-Hill. 2001.
[2] Cotran, Kumar, Collins 6th edition. Robbins Pathologic Basis of Disease. WB Saunders Company. 1999.
[3] Kumar P, Clark M. CLINICAL MEDICINE. WB Saunders 2002 Pg 545-549.
[4] Longmore M, Wilkinson I, Torok E. OXFORD HANDBOOK OF CLINICAL MEDICINE. Oxford University Press. 2001.