Mentally retarded-why the physical deformities?

It may sound stupid, but sometimes I wonder sometimes why people with mental retardation also have physical deformities-like certain facial features. Are there also health problems associated that are more pronounced with these kinds of disabilties?

The facial deformities tie in with the fact that the brain develops alongside other structures of the skull.

Absolutely, Down syndrome usually accompanies a myriad of other physical problems including possible heart disease problems, etc.

Not all developmentally delayed people look strange. Many genetic disorders have a component of retardation. Trisomy 21, Downs’ syndrome, causes short stature, low ears, flat nose, almond eyes lacking epicanthic folds, a simian crease on the hands, with short stubby fingers.

Delay is often missed early because the child doesn’t have any defining features. Here’s an article that addresses some of the various other genetic disorders that can cause delay.

Down Syndrome is a genetic disorder (trisomy-21, meaning the presence of three versions of the 21st chromosome instead of the normal pair.) Most trisomies result in an inviable fetus, but a few of them often result in viable pregnancies. Trisomy-21 can cause all sorts of possible physical disorders including heart defects, immune problems, stunted growth, and other problems. Interestingly, the incidence of certain cancers is drastically lower in Down Syndrome patients as compared to the general population. So the reason that Down Syndrome patients have these physical abnormalities is due to their genetic problems.

Other forms of mental disability do not manifest physical abnormalities – there are plenty of normal looking mentally disabled people. You probably wouldn’t know they have a disability unless you had a conversation with them.

Damn computer ate my reply.

In Down Syndrome, the 21st chromosome carries with it a couple of hundred genes that are inevitable overexpressed when you have the extra (third) 21st. One of more of those genes, when overexpressed and in interaction with other things, may cause the mental retardation, while others may cause the heart defects and joint problems. Others cause the facial features some consider distinctive for Down Syndrome, like the eye folds. I am not sure those would be considered a “defect,” however.

So in the case of Down Syndrome, as I understand it, you have a whole family of genes, all of which may do different things and be expressed in different ways, but what they have in common is that they’re all on the 21st chromosone, and thus they’re all overexpressed. The big mystery is why some people with Down Syndrome have these “defects” and distinctive characteristics and others don’t, and why they vary so much in severity.

I don’t know anything about other kinds of mental retardation or the physical deformities of the face you mention. I wouldn’t rule out the possibility that factors like low muscle tone or lack of awareness about socially acceptable facial expressions contribute to the perception that some mentally handicapped people’s faces are"deformed."

There are multiple issues here -

  1. There are some conditions that cause malformation as well as mental retardation, like trisomy 21. See Smith’s Recognizable Patterns of Human Malformation

  2. Some persons with mental retardation do not display the same ‘neutral mask’ that the rest of us use to blend into society. A person with an otherwise normal face looks unusual if he is walking around with a socially ‘unacceptable’ expression.

  3. You may be seeing someone with a physical disability and just assuming that they are mentally retarded, especially if their speech is slow or difficult to understand: e.g. cerebral palsy, Parkinson’s, MS, whatever.

Down’s syndrome also includes something called The Tetrology of Fallot. It is a moderate to fatally serious malformation of the heart, and its associated blood vessels. Now that the appropriate surgery can be done at birth (And even en utero!) there there is quite a good chance that people with this syndrome can have normal lives, and intelligence. As a matter of fact, even the diminished stature is mostly a consequence of poor circulation during development.

Another factor that leads to the stereotype of “retarded looking” is a close association between general neural diseases and an alteration of muscle tone. If your muscles are not at the proper tension during your skeletal development, your bones grow differently, and you have a facial formation that is identifiably associated with less facile social interactions. It is also often the case that hypo tensive facial muscles are less mobile in emotion, leaving the person “slack jawed” in appearance.

Muscular tension that is socially inappropriate may sound like a small thing, but a rictus looks to a lot of people like a grin. It doesn’t really express humor, but it does resemble a grin enough to make people thing the person is smiling inappropriately. Grinning at a person who is not feeling a pleasant emotion is socially disabling, even when it is understood by the person with a rictus reflex.

The whole set of imprimaturs associated with retardation are a part of general folk knowledge, and are applied by people without any conscious thought.

Tris

Triskadecamus, ToF is only one of the heart defects that can manifest in trisomy 21. It is most common, but Down’s babies can have any of a number of heart defects.

There’s evidence that the central defects (heart, as well as bowel and facies) are genetic misprints.

I helped collect data for a study on that very thing. We did FISH (Fluorescence in situ hybridization) tests on all of the patients with central defects*, even though they had no outward signs of genetic defects. This was the first phase of the study. I was gone by the time they moved on to full chromosome studies.

I’m sorry, I don’t remember the exact percentage of positives, but it was greater than 50%

I couldn’t find anything on the web about the study. I was involved 4 years ago. So, I’m guessing it’s finished.

The only thing I could find, is a study from Brazil.

*Central heart defects: ASD, VSD, AV Canal, ToF, Transposition of the Great Vessels, Hypoplastic Left Heart syndrome, Total Anomalous Venous Return. Coarctation of the Aorta and Aortic stenosis may also be involved.

persistance of fetal circulation aren’t included.

brossa, That’s what we referred to as the “Ugly Baby Book” :smiley:
I know, I’m going to hell.

[hijack]I read in Scientific American or somewhere like that they scientists have cured the mental effects of Down Syndrome (or something much like it) in rats! As in, after they’ve already been born, grown up into adults, and everything.

Freaked me out.

Anyone else see this? Can you provide a cite so people will know I’m not crazy?

[/hijack]

No-one has mentioned Fragile X Syndrome yet. It’s the most common inherited cause of learning disability and autism. FXS is caused by expansion sequences on the X chromosome and thus can be inherited in an X-linked fashion. Characteristic features are large ears, jaw and testicles a long, narrow face, flat feet and hyperflexibilty of the joints.

Frylock- perhaps you were thinking of this study about FXS?

FXS info:


One thing to keep in mind is that there are no genes “for” a particular trait. Although genes have other functions (such as turning on other genes), what they mainly do is code for proteins. Some of these are things like collagen that is structural, or the proteins that make up muscle or other tissue, some are enzymes and some are regulatory, for example. Evolution being inherently conservative, reuses many of the proteins for multiple purposes (depending on the cellular environment). If a gene mutates, a different protein may be coded for, and this could and usually would have multiple effects. To complicate matters, the mutation might affect som uses and not others. And even mutations that do not change the actual protein might change the rate at which it is synthesized (a very recent observation). the upshot of this is that one mutation can have many effects if the protein it codes for has many uses. Trisomy 21 is a special case since it is a whole chromosome that is duplicated (or rather in triplicate, not duplicate), which presumably causes some proteins to appear in too high quantities or maybe regulatory proteins to overdo the regulation or …

Another possibility is that a protein of primary use in the brain is involved in both cognitive and motor functions. In that case, the individual may be both retarded and have coordination problems. I know of one such case, although I have no idea what the cause is.