Yesterday at the store I caught a glimpse of a dad pushing his ~6-month-old twin daughters in their stroller. It could have just been the light, but one of the girls seemed to have the facial characteristics associated with a person with Down’s Syndrome. The other did not.
Is it possible that in a set of twins, one would have a developmental disability and the other wouldn’t?
Of course. Fraternal twins are genetically just like any other pair of siblings. Down syndrome is genetically determined, so it’s perfectly possible for one child to get an extra chromosome and its sibling not to.
Many years ago I read an article in Seventeen magazine by a girl whose twin sister had a developmental disability (although she didn’t call it Down Syndrome) while she (the writer) did not. IIRC, it was called, “My Twin Sister Is Not Just Like Me”.
Two of the kids on “Little People Big World” are twins. One of them is a dwarf, the other not.
What about identical twins and disabilities? What sort of developmental disabilities develop in utero, and could develop after the eggs split?
Cerebral palsy is one example that comes to mind, since it’s not a genetic issue at all, and it’s often caused by issues / injuries which occur during pregnancy or childbirth. OTOH, it’s also a condition which largely affects the body, rather than being a cognitive disability, so I’m not sure if it’d qualify.
My husband works with a guy who has identical twin daughters - one has CP and is in a wheelchair.
Theoretically almost any genetic condition could develop after the zygote splits to form identical twins, including trisomies such as Down Syndrome.
If the fertilized egg splits at the two cell stage then
embryo #1 develops normally as twin #1 and
if embryo #2 has a non disjunction in its next cell division then
[ul][li]embryo #2 has two cells, one with an extra chromosome and one missing a chromosome[/li][li]the cell that is missing a chromosome is not viable*[/li][li]the cell with the extra chromosome grows into twin #2 with Down Syndrome.[/li][/ul]
If the non disjunction event in twin #2 happens at a slightly later state then that twin may have Mosaic Down Syndrome.
Actor Ashton Kutcher also has a twin brother with cerebral palsy.
In fact, everything else being equal, one or both of a set of twins is more likely than a non-twin to develop cerebral palsy (presumably because many of the various risks associated with twinning are, in turn, associated with CP, e.g. low birth weight, prematurity, etc.)
There are two little boys right across the street from me like this. Very sad, but the afflicted twin does seem to have a very good attitude.
Conjoined twin George Schappell has spina bifida. Her sister Lori does not.