It is estimated that 80–99% of people with<unk><unk><unk>  syndrome will have biparietal narrowing (narrowing of skull), ataxia, abnormalities of the neck, and both absent speech development and aphasia. Weak muscle tone (hypotonia) and underdevelopment of many muscles (muscle hypoplasia) are common in children with<unk><unk><unk>  syndrome. Development of joint deformities called contractures, which restrict the movement of certain joints, are common as people age. Mobility is further limited by abnormal muscle stiffness (spasticity), muscle weakness, and involuntary movements of the arms and legs. Many people with<unk>  are unable to walk independently and become wheelchair-bound by adulthood.
Allan–Herndon–Dudley syndrome
Townes–Brocks syndrome
Fryns-Aftimos syndrome
Flynn–Aird syndrome
Kearns–Sayre syndrome
Grisel's syndrome
Dennie–Marfan syndrome
Lujan–Fryns syndrome