Incidence and prevalence of nutritional and hereditary rickets in southern Denmark

Objective To estimate the incidence of nutritional rickets and the incidence and prevalence of hereditary rickets. Design Population-based retrospective cohort study based on a review of medical records. Methods Patients aged 0-14.9 years referred to or discharged from hospitals in Southern Denmark from 1985 to 2005 with a diagnosis of rickets were identified by register search and their medical records were retrieved. Patients fulfilling the diagnostic criteria of primary rickets were included. Results We identified 112 patients with nutritional rickets of whom 74% were immigrants. From 1995-2005 the average incidence of nutritional rickets in children aged 0-14.9 years and 0-2.9 years was 2.9 and 5.8 per 100,000 per year, respectively. Among immigrant children born in Denmark the average incidence was 60 (0-14.9 years) per 100,000 per year. Ethnic Danish children were only diagnosed in early childhood and the average incidence in the age group 0-2.9 years declined from 5.0 to 2.0 per 100,000 per year during 1985-1994 to 1995-2005. Sixteen cases of hereditary rickets were diagnosed during the study period giving an average incidence of 4.3 per 100,000 (0-0.9 years) per year. The prevalence of hypophosphatemic rickets and vitamin D-dependent rickets type 1 was 4.8 and 0.4 per 100,000 (0-14.9 years), respectively. Conclusions Nutritional rickets is rare in Southern Denmark and largely restricted to immigrants, but the incidence among ethnic Danish children was unexpectedly high. Hereditary rickets is the most common cause of rickets in ethnic Danish children, but nutritional rickets is most frequent among all young children.