In Reply.—The parents appear to be normal by physical examination and by serum calcium, phosphorus, parathyroid hormone, and vitamin D metabolite determinations. Furthermore, x-ray films of hands in both parents are normal. We thus have no evidence that the parents are affected; indeed, N-protein determinations were performed on both parents and found to be normal. There is no family history of mental retardation, and the parents are extremely bright individuals who have been a source of intellectual stimulation for us in regard to evaluation of this disorder. Although we were keenly interested in the familial nature of this disorder, we could not find any physical, biochemical, or hormonal evidence of disorders in neither the parents nor the siblings studied thus far.