Prevalence and characteristics of paediatric X-linked hypophosphataemia in Australia and New Zealand: Results from the Australian and the New Zealand Paediatric Surveillance Units survey

X-linked hypophosphataemia (XLH) is the most common heritable form of rickets. Prevalence data varies across the literature between 1 in 20,000 and 1 in 200,000 per population. Australian and New Zealand Paediatric Surveillance Units collected cross-sectional data from paediatricians on existing cases to estimate prevalence and characteristics of paediatric XLH in Australia and New Zealand. Seventy-five cases in Australia and 18 cases in New Zealand were identified. Estimated minimum prevalence based on these cases was 1.33 (1.04–1.66) per 100,000 and 1.60 per 100,000 (95%CI 0.97–2.58) in Australia and New Zealand respectively, with actual prevalence likely higher due to incomplete ascertainment. Despite a family history in most cases, delayed diagnosis was common, with 49 % diagnosed after 2 years of age. Delayed diagnosis was more common in sporadic versus familial cases. Most common clinical characteristics included leg bowing (89 %), bone and joint pain (68 %), abnormal gait (57 %) and short stature (49 %). There was a significant burden of orthopaedic disease and surgeries and a high rate of complications of nephrocalcinosis and hyperparathyroidism (32 % and 20 % respectively). Additionally, while guidelines stress the importance of multidisciplinary care, many did not have access to recommended health professionals, with only 3 % seeing a psychologist and 68 % seeing a dentist. This is despite the high psychological burden of XLH and a significant proportion (41 %) of this cohort having dental issues (tooth abscess, dental capping, tooth extraction). There were two cases from NZ without data available. Of the 91 cases with data collected, 46 % were on burosumab therapy. Consistent with clinical trials, those on burosumab had a higher serum phosphate levels (p