Fibrodysplasia Ossificans Progressiva (FOP) is one of the rarest diseases in the world. Patients with FOP are born with characteristic malformations of the great toes (short and bent, sometimes turning inward), but otherwise these children appear normal.
At age 24, a young woman (let’s call her Ann) was healthy, vibrant, and carefree. After her 25th birthday, Ann began to experience upper limb tremors. Within 4 months, the tremors progressed to all of Ann’s limbs, followed by bouts of mania. Due to the neuropsychological presentations, a psychiatrist prescribed Ann haloperidol, chlorpromazine, and propranolol to treat the mania. A further regimen of levodopa and carbidopa was prescribed by a neurophysician to treat the atypical Parkinson’s.
In genetics, a chimera is an individual with 2 or more distinct, unrelated genetic lineages (ie, 46XX/46XX, 46XX/46XY, or 46XY/46XY). This condition is not to be confused with germline mosaicism, in which a mutation occurs during mitosis, altering part of a genetic line (aneuploidy). In mosaics, typically transcription errors result in a chromosome that may be either duplicated or deleted. The mutated cell is further copied, appearing separate from other cells (46XX/47XX or 46XY/47XY) but in fact, a single lineage exists. An individual with germline mosaicism shouldn’t have any related health issues since it is not a systemic mutation. An example of mosaicism where a systemic mutation exists is Trisomy 21, or Down’s syndrome, where a duplicating error occurs on chromosome 21 affecting all or nearly every cell.
