[2] The causes seem largely not to be in the greater pre- and perinatal biological problems twins may experience, but rather in postnatal factors.
These factors occur within the family environment and include both a reduced quality of verbal stimulation and interaction with adult language models which result from greater demands of care-giving made on parents of twins, and the intensive interaction between twins which may increase their chances of developing cryptophasia and idioglossia at the expense of conventional language.
[4] An article in Slate dealt with what is observed about the social effects of cryptophasia between twins and how it relates to societies.
"[5] June and Jennifer Gibbons were twin sisters living in Wales whose language may have been an example of cryptophasia.
Grace and Virginia Kennedy, born in the United States in 1970, developed their own private language, characterized by an extremely fast tempo and staccato rhythm.