MONDO_0011723 (hemifacial myohyperplasia) (HMH) is a developmental disorder that frequently affects the right side of the face and is commonly seen in males. On the affected side of the face, there are usually enlarged tissues that lead to an abnormal jaw shape. Other features associated with HMH include enlargement of the brain, epilepsy, strabismus, genitourinary system disorders, intellectual disability, and dilation of the pupil on the affected side. Asymmetry of the face is more noticeable with age and remains until the end of adolescence when the asymmetry stabilizes. The cause of HMH is unknown; but theories suggest an imbalance in the endocrine system, neuronal abnormalities, chromosomal abnormalities, random events in twinning and fetal development, and vascular or lymphatic abnormalities.