This simple page has been created to help us understand how the particular gene for Familial Hypophosphatemia is inherited -- thanks to those who have asked the question! Scroll down for more explanatory text below the picture.
In spontaneous cases of hypophosphatemia, during meiosis in either the father's or mother's chromosome, a mutation occurs which forms the genetic makeup of the new individual. That mutation now is part of what is called the germline, so that a spontaneously affected individual will now pass that gene to their children, according to simple laws, even though neither of their parents may have had the gene.
Transmission of a characteristic like the Familial Hypophosphatemia gene (which is on the X chromosome), is easily understood, though it might help to refer to the diagram. Since we each of us have two sets of chromosomes (one from our mother, one from our father), the particular chromosome that we pass down into our gametes (egg or sperm) could be from either one set or the other.
Suppose we're thinking of an affected man (ie a man that has the Familial Hypophosphatemia gene). Since the gene is on his X chromosome, if his partner has a boy (that is, a Y chromosome has come from the man), then the boy will not have the gene. If the couple has a girl, however, then she will be affected, because she will necessarily have the gene from the father's X chromosome.
Suppose we're thinking of an affected woman (ie a woman who has the Familial Hypophosphatemia gene on one of her X chromosomes). When the woman's chromosomes segregate into either of the two sets, then her egg could possess the affected chromosome, or instead, the other unaffected chromosome. Therefore, because there are two sets of chromosomes, there is a 50:50 chance that the affected woman will pass her affected X chromosome to her children (of whatever gender).