Chapter 8 Allgrove J, Shaw NJ (eds): Calcium and Bone Disorders in Children and Adolescents. 2nd, revised edition. Endocr Dev. Basel, Karger, 2015, vol 28, pp 119–133 (DOI: 10.1159/000381000)
A Practical Approach to Vitamin D Deficiency and Rickets Jeremy Allgrove a · Nick J. Shaw b b Department
of Paediatric Endocrinology, Royal London Hospital, Whitechapel, London, and of Endocrinology and Diabetes, Birmingham Children’s Hospital, Birmingham, UK
Abstract Rickets is a condition in which there is failure of the normal mineralisation (osteomalacia) of growing bone. Whilst osteomalacia may be present in adults, rickets cannot occur. It is generally caused by a lack of mineral supply, which can either occur as a result of the deficiency of calcium (calciopaenic rickets, now known as parathyroid hormone-dependent rickets) or of phosphate (phosphopaenic rickets, now called FGF23-dependent rickets). Renal disorders may also interfere with the process of mineralisation and cause rickets. Only parathyroid hormone-dependent rickets and distal renal tubular disorders will be discussed in this chapter. The most common cause of rickets is still vitamin D deficiency, which is also responsible for other problems. Disorders of vitamin D metabolism or responsiveness may also cause similar issues. Distal renal tubular acidosis may also be caused by a variety of metabolic errors similar to those of osteoclasts. One form of distal renal tubular acidosis also causes a type of osteopetrosis. This chapter describes these conditions in detail and sets out a logical approach for treatment. © 2015 S. Karger AG, Basel
Osteomalacia is a condition in which mineralisation of osteoid tissue fails to occur normally, usually because of a deficiency in the supply of mineral, calcium or phosphate for some reason. Although osteomalacia can occur in any individual, rickets can only occur in the presence of unfused epiphyses because it manifests in the growth plate. Therefore, adults cannot suffer from rickets but may develop osteomalacia. There are two principal causes of rickets, which have traditionally been referred to as calciopaenic and phosphopaenic. In addition, a third group of conditions, related to renal tubular disorders, also cause this disorder. Recently, a new classification of rickets has been proposed , in which calciopaenic rickets is now regarded as parathyroid hormone (PTH)-dependent. Phosphopaenic rickets will not be considered in this chapter because it is discussed elsewhere (See Chapter 9). This section will deal only with the various forms of calciopaenic and renal rickets. Downloaded by: UCONN Storrs 188.8.131.52 - 6/17/2015 10:06:23 PM
For a detailed discussion of the physiology of vitamin D, see Chapter 2. Briefly, vitamin D is a secosteroid that is derived principally in the form of cholecalciferol by the action of ultraviolet light on dehydrocholesterol. It then undergoes two metabolic steps, involving a first hydroxylation at the 25-position to form 25OHD and a second hydroxylation at the 1α-position of the steroid molecule to form the active metabolite, 1,25(OH)2D. Following this activation, 1,25(OH)2D acts on classical steroid receptors by participating in ligand binding, followed by transfer to the nucleus and subsequent DNA binding. Defects in any of these processes can give rise to rickets, and a thorough understanding of the various processes is required to be able to make a correct diagnosis so that appropriate treatment can be instigated.
Vitamin D Deficiency
Definition of Vitamin D Deficiency There have been several recent consensus statements or guidelines that have included definitions of vitamin D deficiency. It is generally agreed that the serum concentration of 25OHD is the best marker of an individual’s vitamin D status because it is the major circulating form and reflects the combination of dietary intake and cutaneous skin synthesis. However, different thresholds for the level of 25OHD that is considered to reflect deficiency are used. For example, the Institute of Medicine’s report on the dietary reference intake for vitamin D published in 2010  defined a level of 50 nmol/l as meeting the needs of 97.5% of the population, whereas the Endocrine Society Clinical Practice Guideline published in 2011 defined vitamin D deficiency as a level