If Rett is a continuum, would it be possible for the early regression to occur earlier than 6 months?
Yes, but if someone did have an early regression in that first 6 month period, they would not meet the criteria for classic Rett syndrome. They could potentially meet the criteria for either atypical Rett syndrome or variant Rett syndrome. Often when a diagnosis is made, the parent or other individual is reporting the history, and so if you have a history that motor milestones were delayed in that first 6 month period, the individual will not meet the criteria for classic Rett syndrome, but could get the variant diagnosis.
Theresa Bartolotta, Ph.D., CCC-SLP is Associate Professor of Speech-Language Pathology and Director of Assessment in the Office of the Provost at Seton Hall. Her primary research interests are in communication impairment in autism spectrum disorders, including Rett syndrome. She has published articles and presented widely on Rett syndrome and communication intervention in this population.