Very rarely are we able to determine the reason or cause of the genetic mutation in a family. Autosomal dominant conditions usually occur when just one copy of a pair of genes does not work correctly. Because the VHL gene is a tumor suppressor gene, tumors and cysts arise after the second copy of the VHL gene becomes altered or mutated within a cell. Males and females can equally inherit the mutated VHL gene. A child who does not inherit the mutated gene will not develop VHL and cannot pass VHL on to the grandchildren.
Fertilization occurs when a father's sperm and mother's egg unite at the time of conception.
A short time later, within the fertilized cell, the DNA copies itself and the cell divides, becoming two cells, each with identical chromosomes, identical DNA and genes. This is the process of mitosis or cell division. This is the process of cell differentiation, which will have more meaning when mosaicism is discussed below. At the time of fertilization, the child received the mutated VHL gene from the affected parent, and every cell thereafter will have the same VHL mutation. From the time the first heritable VHL mutation occurs, the family from that point on has an autosomal dominant genetic condition that may be passed down through the generations.