<s>[INST] <<SYS>> This is a medical question of type : inheritance <</SYS>> Is tetrasomy 18p inherited ? [/INST] Tetrasomy 18p is usually not inherited. The chromosomal change responsible for the disorder typically occurs as a random event during the formation of reproductive cells (eggs or sperm) in a parent of the affected individual, usually the mother. Most affected individuals have no history of the disorder in their family. However, rare inherited cases of tetrasomy 18p have been reported. </s>