Hybrid growth disorders refer to reduced growth or overgrowth in an organism that is a hybrid of two different species. In some sense, it is a type of hybrid dysgenesis when the growth disorder proves deleterious, thus making it the opposite of heterosis or hybrid vigour.
Hybrid growth disorders may be referred to as a growth dysplasia, especially when resulting in overgrowth, although this terminology may be confusing since the term dysplasia is commonly used to imply an impending cancer. However, a hybrid growth disorder is not caused by cancer.
A study on hybrid mice which investigated the possible causes for hybrid growth disorders revealed gene imprinting to have a major effect. The study also showed that the growth disorder most commonly affected the heterozygous sex, as expected by Haldane's rule. This would also explain why hybrid growth disorders often appear to affect one sex more than the other.