Presentation of vitamin D deficiency(,,,,,frontal bossing of the skull)

The past few decades have seen a resurgence of vitamin D deficiency rickets in developed countries, particularly in dark skinned infants who are exclusively breast fed for prolonged periods without additional vitamin supplements.^1–5 Vitamin D and its metabolites are required for calcium absorption from the gut and adequate delivery to the bone to promote normal bone mineralisation.⁴ Vitamin D deficiency results in reduced serum calcium, which triggers secretion of parathyroid hormone (PTH) to release calcium and phosphorus from bone in an attempt to maintain normal serum calcium levels.⁴ The consequence is usually rickets in children, which is defined as failure of mineralisation (osteomalacia) of growing bone or osteoid tissue. Children with vitamin D deficiency classically present soon after weight bearing age with bony abnormalities such as bowing of the legs, knock-knees, rickety rosary of the costo-chondral junctions, swelling of the ends of long bones, frontal bossing of the skull, and pathological fractures in severe cases, as well as poor growth, delayed dentition, and slow motor development.^4,6 However, another group of children with vitamin D deficiency has been described, who present with symptoms of hypocalcaemia (neuromuscular irritability, including convulsions, tetany, and paraesthesia) with or without radiological evidence of rickets;^5,7–11 it has been suggested that this is an early phase (stage 1) of vitamin D deficiency which usually occurs in young infants below 6 months of age.¹² To date, there have been no studies to identify any differences between these two groups that might explain such contrasting

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