MRXSA is an X-linked recessive neurodevelopmental disorder characterized by global developmental delay with impaired intellectual development, usually accompanied by walking difficulties and poor or absent speech. Affected individuals have dysmorphic features, including large head circumference, downslanting palpebral fissures, bulbous nose, high-arched palate, short stature, and small hands and feet. Ocular anomalies, including strabismus, exotropia, myopia, and keratoconus, are common. Some patients may develop seizures. Additional variable features, such as mild congenital heart defects, joint stiffness, renal anomalies, and hemangiomas, may also be present (summary by Lee et al., 2020).

This multisystem disorder is characterized by moyamoya disease, short stature, hypergonadotropic hypogonadism, and facial dysmorphism. Other variable features include dilated cardiomyopathy, premature graying of the hair, and early-onset cataracts. Moyamoya disease is a progressive cerebrovascular disorder characterized by stenosis or occlusion of the internal carotid arteries and the main branches, leading to the development of small collateral vessels (moyamoya vessels) at the base of the brain. Affected individuals can develop acute neurologic events due to stroke-like episodes (summary by Miskinyte et al., 2011). For a general phenotypic description and a discussion of genetic heterogeneity of moyamoya disease, see MYMY1 (252350).