Endocrine Abstracts

Rickets is a disorder in which defective mineralisation of the growth plate occurs in growing children. The aetiology is due to deficiency of calcium and/or phosphate with hypophosphataemia being pivotal in the pathogenesis of all forms of rickets. It is convenient to classify rickets as calcipenic or phosphopenic depending on whether there is predominantly a deficiency of calcium or phosphate.

Although nutritional rickets is the most well known and prevalent form of rickets in the world there are a variety of rarer genetically determined causes. Principal amongst these is hypophosphataemic rickets where an understanding of the role of FGF23 has led to identification of several primary forms. The X-linked dominant form is the commonest for which a new treatment option with an FGF23 antibody is emerging. The role of activating somatic mutations in the RAS pathway in causing rickets in epidermal naevus syndromes has recently been recognised.

There are a variety of other secondary causes of hypophosphataemia,most of which are due to renal tubular loss of phosphate eg McCune Albright Syndrome. However dietary phosphate deficiency is also a potential cause with the recent recognition of the role of exclusive elemental formula feeds such as Neocate.

Disorders in the Vitamin D metabolism pathway are also important to recognise and distinguish from nutritional rickets as they often occur in the same ethnic groups. These will require long term treatment with a Vitamin D analogue such as Alphacalcidol or Calcitriol rather than Vitamin D as used in nutritional rickets. This talk will provide an overview of rarer causes of rickets and will hopefully lead to early recognition by clinicians.