Low breast milk phosphorus concentration in familial hypophosphatemia.

We report breast milk mineral concentrations in a mother with familial hypophosphatemia that was untreated due to poor compliance with medical advice. Milk phosphorus content was extremely low despite normal maternal serum phosphorus concentrations. Milk calcium concentrations were only modestly decreased so that the ratio of calcium to phosphorus was greatly elevated. It appears that mothers with this disorder who breast feed should have their milk mineral content carefully monitored during lactation. If milk mineral content is abnormal despite maternal therapy with phosphorus and vitamin D, infants may require supplementation of mineral intake.