PTH and Hypocalcemia: While patients affected by OCS are usually stillborn or die shortly after birth, the allelic disorder known as Kenny-Caffey syndrome (KCS) shows a milder phenotype with impaired skeletal development, small and dense bones, short stature and no life-threatening complications, except for recurrent hypocalcemia with low levels of parathyroid hormone (PTH), which requires continuous therapy with calcium and activated vitamin D [5,6,7].