Table 1.

Consensus criteria for classic and variant Rett syndrome (RTT) [52]

Requirement for classic or typical RTT	A period of regression followed by stabilization and recovery: 1. All main and all exclusion criteria 2. Supportive criteria not required although may be present
Requirement for variant or atypical RTT	1. A period of regression followed by stabilization and recovery 2. At least 2 of 4 main criteria and 5 of 11 supportive criteria
Main criteria	1. Partial or complete loss of acquired purposeful hand skills 2. Partial or complete loss of spoken language 3. Dyspraxic gait or inability to ambulate 4. Stereotypic hand movements: hand mouthing, hand wringing/clasping, hand clapping, or finger rubbing
Exclusion criteria	1. Brain injury: peri- or postnatal trauma, neurometabolic disease, or severe infection involving neurological function 2. Grossly abnormal psychomotor development in first 6 months after birth
Supportive criteria for variant RTT	1. Periodic breathing during wakefulness 2. Bruxism while awake 3. Altered sleep pattern 4. Abnormal muscle tone 5. Peripheral vasomotor disturbance 6. Scoliosis/kyphosis 7. Growth failure 8. Small cool/cold hands and/or feet 9. Inappropriate laughing or screaming spells 10. Delayed or diminished response to pain 11. Intense eye communication or “eye pointing”