Doctors diagnose Rett syndrome by observing signs and symptoms during the child's early growth and development, and conducting ongoing evaluations of the child's physical and neurological status. Recently, scientists developed a genetic test to confirm the clinical diagnosis of this disorder; the test involves searching for the genetic mutation on the child's X chromosome. Given what we know about the genes involved in Rett syndrome, such tests are able to confirm a clinical diagnosis in up to 80 percent of all cases.
Some children who have Rett syndrome-like characteristics or genetic mutations do not fulfill the diagnostic criteria for the syndrome as defined below. These persons are described as having "atypical" or "variant" Rett syndrome.
A pediatric neurologist or developmental pediatrician should be consulted to confirm the clinical diagnosis of Rett syndrome. The physician will use a highly specific set of guidelines that are divided into three types of clinical criteria: essential, supportive, and exclusion. The presence of any of the exclusion criteria negates a diagnosis of "classic" or "typical" Rett syndrome.
Examples of essential diagnostic criteria or symptoms include having apparently normal development until between the ages of 6 and 18 months and having normal head circumference at birth followed by a slowing of the rate of head growth with age (between 3 months and 4 years). Other essential diagnostic criteria include severely impaired expressive language, repetitive hand movements, shaking of the torso, and toe-walking or an unsteady, wide-based, stiff-legged gait.
Supportive criteria are not required for a diagnosis of Rett syndrome but may occur in some patients. In addition, these symptoms — which vary in severity from child to child — may not be observed in very young girls but may develop with age. A child with supportive criteria but none of the essential criteria does not have Rett syndrome. Supportive criteria include breathing difficulties; electroencephalogram (EEG) abnormalities; seizures; muscle rigidity, spasticity, and/or joint contracture which worsen with age; scoliosis; teeth-grinding; small feet in relation to height; growth retardation; decreased body fat and muscle mass (although there may be a tendency toward obesity in some affected adults); abnormal sleep patterns, irritability, or agitation; chewing and/or swallowing difficulties; poor circulation of the lower extremities with cold and bluish-red feet and legs; decreased mobility with age; and constipation.
In addition to the essential diagnostic criteria, a number of specific conditions enable physicians to rule out a diagnosis of Rett syndrome. These are referred to as exclusion criteria. Children with any one of the following criteria do not have Rett syndrome: enlargement of body organs or other signs of storage disease, vision loss due to retinal disorder or optic atrophy, microcephaly at birth, an identifiable metabolic disorder or other inherited degenerative disorder, an acquired neurological disorder resulting from severe infection or head trauma, evidence of growth retardation in utero, or evidence of brain damage acquired after birth.
Sources:
http://www.ninds.nih.gov/disorders/rett/detail_rett.htm
http://ghr.nlm.nih.gov/condition=rettsyndrome
