Curtiss (1977) - Genie
This reported the case of a girl who suffered extreme cruelty from her parents, and never formed any attachments. Her father kept her strapped to a high chair with a potty in the seat for most of her childhood. She was beaten if she made any sounds, and didn't have the chance to play with toys ot with other children.
She was discovered when she was 13 years old. She was physically undeveloped and could only speak with animal-like sounds.
After a lot of help she later learned some language but her social and intellectual skills never seemed to fully develop.
Koluchova - Czech twin boys
This is the case of twin boys whose mother died soon after they were born. Their father remarried and their stepmother treated them very cruelly. They were often kept locked in a cellar, beaten and had no toys.
They were found when they were seven with rickets (a bone development disease caused by a lack of vitamin D), and very little social or intellectual development.
They were later adopted and made lots of progress. By adulthood that have above average intelligence and had normal social relationships.
Differences Between Genie & the Czech Twins
Differences between the cases might explain why the Czech twins recovered better than Genie.
1) The length of privation and how old the children were when they were discovered - the Czech twins were much younger than Genie, so still had time to develop once they were in a better environment.
2) Their experiences during the isolation - the twins where kept together, so they may have attached to eachother.
3) The quality of care they received after the isolation - the twins were adopted, but Genie was passed between psychologists and evenually put in an institution.
4) Individual differences, including ability to recover.
The evidence suggests that recovery from privation is possible.