Endocrine Abstracts

Background: The extent of biochemical abnormalities in household members of children presenting with symptomatic vitamin D deficiency remains unknown. Characterising risk groups who warrant 25 hydroxyvitamin D (25OHD) testing will help reduce the rising frequency of unnecessary testing in the UK.

Aims: Investigate the prevalence of vitamin D deficiency and biochemical osteomalacia in the mothers and siblings of children presenting with symptomatic vitamin D deficiency. Identify risk factors for severe deficiency in family members.

Methods: All mothers and sibling of children referred to a single tertiary endocrine centre between January 2018 and December 2021, with symptomatic vitamin D deficiency were investigated prospectively for vitamin D deficiency [defined as 25OHD< 30nmol/l] and biochemical osteomalacia [vitamin D deficiency and elevated alkaline phosphatase (ALP) and/or parathormone (PTH)] as per clinical guidelines.

Results: Ninety-seven family members (68 siblings and 29 mothers) of 29 index cases (median age 1.7 years, 55.5% male) were investigated. The majority (65.5%, n=19) were of Asian ethnic background. The mean (SD) 25OHD levels of the index, maternal and sibling cohorts were 15 (10), 15 (7) and 20 (10) nmol/l respectively. Vitamin D deficiency was noted in 93% of the maternal and 79% of the sibling cohorts. Biochemical osteomalacia was present in 72% of the maternal and 79% of the sibling cohorts. Mothers of infants had significantly lower mean 25OHD levels compared to mothers of older children [11 (n=12) vs 18 nmol/l (n=17) respectively, P=0.006)], most of whom were symptomatic (66.6%, n=8/12). Among the 10% (n=7) of the siblings with hypocalcaemia, 86% (n=6/7) had concurrent dietary calcium deficiency and 71.4% (n= 5/7) reported symptoms in retrospect. Hypocalcaemic siblings had significantly lower 25OHD (7 vs 15 nmol/l, P<0.001), higher PTH (175 vs 58 ng/l, P<0.001) and ALP (846 vs 318 IU/l, P<0.001), respectively compared to normocalcaemic siblings.

Conclusions: We recommend universal vitamin D supplementation of all family members of children diagnosed with symptomatic vitamin D deficiency. Biochemical testing is indicated in those at highest risk such as mothers of infants, individuals with concurrent dietary calcium deficiency and those with clinical symptoms.