This progressive X-linked mental retardation
affects boys (moderate mental retardation) more often and more severely than
girls (mild mental retardation). The main neurologic symptoms include
delayed language skills, delayed motor development, autism or autistic-like
behavior, behavioral problems (attention deficit hyperactivity disorder,
oppositional defiant disorder, enuresis, encopresis), and poor sensory
skills. Anatomical features may include macrocephaly, a long face with
prognathism (which in fact is often just a prominent symphysis of the
mandibula rather than real prognathism), strabismus, prominent large ears,
high arched palate, and a high-pitched voice. The external male genitalia
show pronounced growth during puberty, which results in macroorchidism.
Overall, muscle tone is low with generalized joint laxity (particularly of
the fingers). Pectus excavatum, flat feet, shortening of the tubular bones
of the hands, and hyperlordosis may be present. Heart defects (e.g., mitral
valve prolapse), dilatation of the aortic root, and seizures have been
described. Researchers found that the hippocampus often shows an age-related
increase in size, whereas the superior temporal gyrus and the posterior
cerebellar vermis are diminished in size. After age 50 years, patients show
an increased rate of progressive parkinsonism, cognitive decline, and
generalized brain atrophy.