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.

Lysosomal cystine storage in cystinosis and mucolipidosis type II.

Cultured fibroblasts from mucolipidosis II (ML-II) patients demonstrated an elevated cystine content which increased with time in culture compared to fibroblasts from cystinotic patients or normal controls under the same conditions. In both cystinotic and ML-II cells the increased levels of cystine could be derived either from endogenous proteolysis or from in vitro supplementation of the cultured cells with cysteine-glutathione mixed disulfide. Cystine was depleted from both cell types by cysteamine. When cysteamine was replaced with complete medium, the cystine reaccumulated in both cystinotic and ML-II cells within 24 h, although a lag of 4 h was seen with ML-II cells. The intracellular location of the increased cystine in cultured fibroblasts was examined utilizing free-flow electrophoresis and found to be in the purified population of secondary lysosomes of both cystinotic and ML-II cells. White blood cell and hepatic cystine, which was greatly increased in cystinotic patients, was not elevated in ML-II patients. Compared to normal control fibroblasts the efflux of cystine from isolated granular fractions was virtually absent in cystinotic fibroblasts and considerably reduced in ML-II fibroblasts. The examination of such similarities and differences in cystine accumulation and transport in tissues from cystinotic and ML-II patients has provided some insight into the defects in these diseases.