Coexistence of hypocalciuric hypercalcaemia and interstitial lung disease in a family: a cross-sectional study

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Abstract
A large kindred (21 subjects) with unexplained association of familial hypocalciuric hypercalcemia and idiopathic interstitial lung disease was studied. Serum Ca was increased in 15 patients (the youngest being 7 yr old) and was associated with hypo- or normocalciuria. The abnormalities were not age-dependent. The serum concentrations of parathyroid hormone, 25-hydroxyvitamin D3, 1,25-dihydroxyvitamin D3 and calcitonin were normal. In 12 patients the diffusing capacity (DLCO) and/or DLCO per unit lung volume was < 75% predicted. This was often accompanied by a vital capacity of < 80% predicted, an increased Tiffeneau index and a reticulo-micronodular pattern with high diaphragm on chest X-ray. The decrease in DLCO was more pronounced in older non-smoking as well as smoking subjects (P < 0.02) suggesting a progressing interstitial disease with age. The fibrosing alveolitis, which was confirmed by open lung biopsy in 3 subjects, was not attributed to sarcoidosis, collagen-vascular disease or exogenous causes. The disturbances in the Ca homeostasis and in the diffusing capacity of the lung coexisted in 7 of the 21 patients. Apparently, both abnormalities were inherited following an autosomal-dominant pattern but with a different penetration in each person, and seemed not to be causally related to each other.