Yes, you can have CMT without having inherited it from a parent. CMT is inheritable because the genetic mutations that cause CMT can be passed on. These same mutations, however, can occur on their own without having been inherited. When somebody has CMT without having inherited it from a parent, their CMT is referred to as a de novo case. De novo means new.
A de novo CMT case is CMT that was caused by a genetic mutation that occurred randomly, spontaneously at or shortly after conception. Rather than a parent passing down the genetic mutation, the mutation occurred on its own. When somebody has a de novo CMT case, the chances for them to pass it on to their children are the same as though they had inherited it. The only difference between a de novo case of CMT and CMT that was inherited is that a de novo case is caused by a genetic mutation that was not inherited.
De novo mutations are not unique to CMT. They occur across many genetic diseases and are well-documented in genetics. What makes de novo CMT cases particularly important is the impact on family history. Someone with a de novo case has no family history of CMT at all, which can delay diagnosis or lead a clinician to rule CMT out prematurely. A negative family history does not mean CMT is off the table.
