Mendel didn't know the half of it

[electricland]

Neurofibromatosis is considered to have an autosomal dominant pattern of inheritance because affected people may have affected relatives in successive generations (such as parents and children). Unlike other autosomal dominant conditions, however, two copies (instead of one copy) of the NF1 or NF2 gene must be altered before the condition's characteristic features will develop. People with neurofibromatosis are born with one mutated copy of the gene in each cell. Then, during their lifetime, a second mutation occurs in the other copy of the gene in nerve cells or specialized cells surrounding nerves, triggering tumor formation. Almost everyone who is born with one NF1 or NF2 mutation acquires a second mutation in many cells during their lifetime and develops the signs and symptoms of neurofibromatosis.

*sigh*