Why do people with Down Syndrome have that same “look” to them?
Down’s syndrome is caused by trisomy 21 –which means patients have three copies of chromosomes 21 instead of two. In essence their bodies are overdosing by 50% on every protein encoded on chromosome 21. All sorts of proteins have specific roles in early development so the results of messing with the same ones by the same amount are going to be fairly consistent across patients.
Grim fun fact, the only other chromosomes that you can survive a miscount on are X and Y. The other numbered chromosomes are all critical enough that it’s nearly impossible to survive past infancy with the wrong count.
Let’s say you are building a house and you have gone to buy supplies but somehow you accidentally print two copies of the list of doors.
You buy double the doors you need, because you followed the list. No takebacks, you just have to figure out how to use double the amount doors. The room layout is the same- you aren’t making more rooms or even doorways, but you have to do something with them otherwise you are just going to be tripping over a giant pile of doors in the living room.
Maybe you use one door as a countertop. Ok, that was useful (There are some conditions that people with down syndrome don’t get). We finally just start mounting doors everywhere until all the extra doors are used up, so we might have three doors in a bedroom and only one of them goes anywhere. This makes things confusing- every time you go out of a room, you have to pick the right door, and this confusion slows you down a little and makes your house look kinda weird – every room has several nonfunctional doors.
Down syndrome is the same – an extra copy of a chromosome means the body is constantly following two instructions instead of one. This changes how the body is formed and how the pieces work together. Since Down syndrome is very common (about 1/700 births), you see many of the same physical distinctions that come from having that particular extra instruction.
Not just DS. What used to be called fetal alcohol syndrome (permanent effect on the child when a pregnant person dranks alcohol) has very marked physical features on the child, often on the shape of the ears.
Edit: drinking while pregnant causes a lot more damage to the child than physical defects and abnormalities so please don’t.
Funny thing is that you can kinda tell what degree of Down syndrome a person has by their looks. Some have that very distinct look, but some just slightly and you’re not 100% sure. I have a friend who’s brother has Down syndrome but he is generally quite “normal” and he also looks quite “normal”. I’ve also seen a pretty severe case and yea you can instantly tell.
I won’t bore you with the specifics regarding aetiology, but essentially Down’s is due to a an extra chromosome leading to significant neural and physical defects, one of which is their ‘same look’ as you term it.
Those with Down’s appear to have a significant degree of deficiency in midfacial area, mandibular area, and endocranial area1, perhaps due to muscular atrophy caused by the disease.
Otherwise, why they look similar is down to human conditioning. In simple terms, we are very adept at noticing facial differences in our own race, however often, we look at other races, black, asian etc. and cannot differentiate as well between the faces2. This is what occurs with those with Down’s syndrome; we see a similar trait and assume they all ‘look the same’. This is obviously not the case as those with Down’s syndrome often have very different features, but we can’t see past this human trait of recognising those similar to us, far better.
TL:DR – Down’s syndrome sufferers look the same as each other, much the same as other races often look similar as a group, due to a human conditioning effect called the ‘Other Race Effect’^3.
As far as my own research can ^tell!
Fink GB, Madaus WK, Walker GF. A quantitative study of the face in Down’s syndrome. Am J Orthod. 1975;67(5):540-53.
Bar-haim Y, Saidel T, Yovel G. The role of skin colour in face recognition. Perception. 2009;38(1):145-8.
Anzures G, Kelly DJ, Pascalis O, et al. Own- and Other-Race Face Identity Recognition in Children: The Effects of Pose and Feature Composition. Dev Psychol. 2013;
Courtesy of /u/jazzamk in 2015