Are there some people with Down syndrome who are mentally normal?

[nearwildheaven]

@inuittagluuqqak

One thing I’ve wondered about: Are there any genetic benefits arising from Trisomy 21? Are there some genes on chromosome 21 for which it is more beneficial to have three copies of that gene than two copies? The substances produced by the genes on chromosome 21 are produced at a 1.5 times higher quantity in a person with Downs than a person without Downs, so maybe for some of these substances, having a higher quantity is better. For instance, I’ve heard that many common types of cancer are much less common in people with Trisomy 21 than in the general population. This is probably because they have three rather than two copies of certain tumor-suppressor genes found on chromosome 21.

I’m guessing that they don’t usually live long enough to get most types of cancer associated with old age, and when they do, it’s not treated as aggressively as if they were “normal”. They are more likely to get certain types of leukemia, and if they live into their 40s or beyond, they often develop an Alzheimer’s-like syndrome.

[inuittagluuqqak]

The following is stated on the wikipedia article on Down syndrome:

Although the general incidence of cancer amongst individuals with Down syndrome is the same as in the general population,[33] there are greatly reduced incidences of many common malignancies except leukemia and testicular cancer.[34] People with Down syndrome also have a much lower risk of hardening of the arteries and diabetic retinopathy.[35]

Hematologic malignancies such as leukemia are more common in children with DS.[36] In particular, acute lymphoblastic leukemia is at least 10 times more common in DS and the megakaryoblastic form of acute myelogenous leukemia is at least 50 times more common in DS. Transient leukemia is a form of leukemia that is rare in individuals without DS but affects up to 20 percent of newborns with DS.[37] This form of leukemia is typically benign and resolves on its own over several months, though it can lead to other serious illnesses.[38] In contrast to hematologic malignancies, solid tumor malignancies are less common in DS, possibly due to increased numbers of tumor suppressor genes contained in the extra genetic material.[39]

So, if wikipedia is correct, people with Down syndrome are at a greatly increased risk for some types of cancer and a greatly reduced risk for others, with the overall incidence of cancer being about the same as in the general population. Also worth noting is their greatly reduced risk of hardening of the arteries and diabetic retinopathy.

[monstro]

@inuittagluuqqak

One thing I’ve wondered about: Are there any genetic benefits arising from Trisomy 21? Are there some genes on chromosome 21 for which it is more beneficial to have three copies of that gene than two copies? The substances produced by the genes on chromosome 21 are produced at a 1.5 times higher quantity in a person with Downs than a person without Downs, so maybe for some of these substances, having a higher quantity is better. For instance, I’ve heard that many common types of cancer are much less common in people with Trisomy 21 than in the general population. This is probably because they have three rather than two copies of certain tumor-suppressor genes found on chromosome 21.

There was once a girl in my yoga class who had Down’s Syndrome. I noticed that while we were seated in cross-legged pose, her thighs were practically flush with the floor. Indicating that she was insanely flexible.

Hyperelasticity of joints and connective tissues is a symptom of Down’s. It has more disadvantages than advantages, but I’m sure in some circumstances (such as auditioning as a contortionist), it could come in handy.

The truth is that most mutations are either going to have neutral or deleterious effects, because genes and traits don’t work in isolation. A mutation that causes your brain to grow twice as large as normal is pretty worthless unless there’s another set of mutations that allow for adjustments in bone, blood vessel, and connective tissue growth. The chances that one gene’s mutation will be accompanied by all the “right” mutations somewhere else is pretty dang-on slim.

[DSeid]

Hmmm. Looking up their citation we find a study that looked at what was put on death certificates. Looking for other studies besides the one I alreeady linked to I find this one which comes down in the middle:

The risk ratio for all cancers combined, including leukaemia, was 2.7 (1.8 to 3.9). The risk ratio for cancers excluding leukaemia was 1.2 (0.6 to 2.2). Our results showed a significant increase in testicular cancer in people with Down’s syndrome … The level of risk of leukaemia found by us is very similar to the 20-fold increase quoted in standard texts.1,2 It is noteworthy that the data in an administrative NHS statistics database can indeed be used to quantify such a risk reliably. Other studies of linked datasets have also identified the high risk of leukaemia.14–16 These findings support the validity of the study methods in assessing levels of risk for the other diseases studied.

It is sometimes considered that the risk of leukaemia is particularly high for acute myeloid leukaemia, but we found similarly high risks for both myeloid and lymphoid forms. Our data add some evidence to the suggestion that there is an increase in the risk of testicular cancer. The elevated risk of leukaemia can be considered in the broader context of how much the overall risk of cancer is increased: in our data, the overall risk is 2.9 times that of the general population in the age range and follow up periods studied.

No protective effect on any cancer found in that study, overall an incresed risk, but pretty much exclusively becasue of the increase in leukemia.

Looking for more I found this, which provides more detail about life expectancy (now into 50s and some into 60s) and the following comment about the studies that do seem to show lower rates of some solid tumors.

Possible explanations for the decreased risk of some cancers among adults with DS are that accurate population morbidity studies are rare. It has also been proposed that individuals with DS may be less exposed to environmental contributors to cancer risk (Satgé et al., 1998). Decreased alcohol and tobacco use, early menopause and other lifestyle and environmental factors may contribute to lower cancer risk. However, obesity and the lack of physical activity common in adults with DS would contribute to an increased risk of cancers. The shorter life expectancy of individuals with DS has also been suggested to contribute to lower risk for cancer (Satgé et al., 1998). However, as the life expectancy of individuals with DS has increased dramatically over the last few decades, shorter life expectancy becomes a less probable explanation for the apparent lower risk of solid tumors. Several tumor-suppressor genes have been identified on chromosome 21, potentially contributing to the decreased risks for many solid tumors (Lee, T. Park, S. Park & J. Park, 2003). Copper-zinc superoxide dismutase, also located on chromosome 21, and its contribution to the metabolism of oxygen free radicals are further hypothesized to reduce the risk of carcinogens (de la Torre, Casado, Lopez-Fernández, Carrascosa, Ramirez & Saez, 1996).

So while overall cancer is higher there may indeed be lower rates of some cancers. Sorry for having stated otherwise.