Patient Description: The authors describe a female patient with developmental regression and a de novo, likely pathogenic mutation in CACNA1A who meets 3 of 4 main criteria (stereotypic hand movements, loss of purposeful hand movements, gait disturbance), and 6 of 11 supportive criteria (impaired sleep, abnormal tone, vasomotor disturbance, scoliosis, growth retardation, and screaming spells) for atypical Rett syndrome.