You might have seen it.
An adult, with a noticeable smile gap, cuddling up to a youngster, for whom they are an unexpected but welcome addition.
Or perhaps you were lucky enough to witness a momentous occasion; a romantic reunion, your child graduating from school, a child finally crossing the road on his or her own and reaching adulthood.
Such reunions can be emotionally charged. And when it comes to children with facial differences, the details of that reunion tend to vary.
For instance, some children can be indistinguishable from their siblings. Others could not even recognise them as themselves.
What about other families? Surely they remember every moment of the first day their daughter walked out of hospital and walked into their lives?
For other parents, the reunion could be lengthy and frustrating: it could take months, if not years, before the child recognises them.
All of this makes the story of the child with the evident smile gap hard to remember, or remember quickly.
And then there are the children for whom the smile gap is significant.
Some parents find that such children feel inferior to other children and need extra attention. They may still find it difficult for them to focus during their lessons, or to act like normal children.
And what about the child who recognises only their parents’ faces? Their perception of their family is distorted.
Whether this can be resolved, is possible, or even beneficial depends on the level of difficulty and how large the smile gap is.