Nov 19 2008

Somali Autism Cluster

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Recently there has come to attention a potential cluster of autism cases among Somali immigrant in Minnesota and Sweden. If true, this could potentially be an important clue as to the pathophysiology of some types of autism.

Autism is unknown in Somalia, but the children of Somali immigrants in two communities in Minnesota and Sweden have reported higher numbers of cases than the general population. This suggests that there is an environment trigger – something they are getting or not getting in their new communities that is different than Somalia. This report indicates:

In Minneapolis, Somalis account for 6 percent of the city’s public school population, but make up 17 percent of early childhood special education students who have been labeled autistic, according to data aggregated by the Minneapolis Public Schools.

But we need to slow down – apparent clusters of diseases are reported all the time. Most of the time the clusters are not real, meaning they are just statistical flukes. So the first question to answer with any apparent cluster is – does this represent a real epidemiological phenomenon.

With regard to the Somali autism clusters this question has not yet been answered. There is enough anecdotal evidence to warrant more definitive investigation. Somali parents certainly believe they are experiencing something new, and some pediatric neurologists in these areas have had their suspicions also. But this is not enough to form a scientific conclusion – only to justify further research.

The true autism rate in Somalia needs to be investigated also. We should not assume that because the culture does not recognize autism it does not exist.

One problem with the cluster hypothesis is that other immigrant Somali communities have not experienced increased autism rates. If there is an environmental trigger causing the two identified clusters, why are there not clusters in these other communities?

If it turns out to be true that autism rates have significantly increased in some Somali immigrant communities, above what is seen in Somalia or in non-Somali in the same communities, then we can conclude that something is going on and a potential trigger should be sought.

It also has to be noted that autism is really a collection of diseases, not a specific disease. So we may be seeing a new entity that has clinical overlap in features and symptoms with recognized forms of autism.

We see examples of this in neurology all the time. For example, there is a cluster of ALS in Guam. This is likely due to a toxin from the local cycad seeds which are used by the locals (perhaps concentrated in fruit bats which they eat). But this form of ALS does not necessarily have anything to do with sporadic ALS outside of this cluster – different diseases with the same or similar clinical outcomes.

If the Somali autism clusters are real, one potential cause has already been proposed – vitamin D.  Dark-skinned Africans who migrate to northern climates often suffer vitamin D deficiency, which is made in the body through exposure to sunlight. It is possible that Somali immigrants are simply not getting enough vitamin D from the northern sun in Minnesota and Sweden, and low levels of vitamin D are increasing the risk of neuro-developmental disorders with features of autism (or autism itself).

Vitamin D deficiency has been recognized as a contributing factor in some neurological diseases, and has been raised as a potential autism trigger even before the apparent Somali clusters. This does not change the fact that there is copious evidence that autism is largely genetic. But environmental factors can influence the expression of genetic disorders, so even for a dominantly genetic disorder, an environment trigger can be playing a role.

Another intriguing possibility is that these isolated clusters are due to the “founder effect.” When a small isolated population happens to contain an individual or family with a mutation for a disease, subsequent generation may have a cluster of that disease because of increased marriage within a small genetic pool. This would explain why some immigrant communities have had apparent clusters and others have not – it all depends on the founding immigrants. This hypothesis can be tested by looking at family histories within these communities.

Incidentally, vaccines are certainly not playing a role in these alleged clusters. Thimerosal, the mercury-based preservative in some vaccines and a popular target for anti-vaccinationists, was removed from Swedish vaccines prior to the Somali immigration in the 1990’s.  It was also removed from childhood vaccines in the US by 2002.

It seems, however, that the whiff of a possible environmental trigger (like blood in the water) is enough to attract the anti-vaccinationists, even if that trigger is not vaccines.  Anti-vaccine crank David Kirby is already sizing up this issue for his usual hack treatment. He is trying to portray as yet another case of parents trying to look out for their children having to fight an uncaring system. Kirby has only a few themes, and this is one of them.

He writes:

When I first wrote about the large number of Somali children with autism in Minneapolis, back in August, I was contacted by a young mother named Idil, who told me she had been trying for more than a year to get Minnesota officials to pay attention to all the sick kids in the local Somali community.

He then follows with letters from a concerned Somali mom to these Minnesota officials. He is playing the – “If only scientists would listen to the moms”- card. Meanwhile, the issues seems to be getting appropriate attention. As I outlined above, there are many scientific questions that need to be answered.

I know that when you are a parent of a sick child the gears of science may grind maddeningly slowly, and no amount of funding or attention is enough. I also know that squeaky wheels get the grease – so I have no problem with parents squeaking away to advocate for their issues. I do have a problem with crank journalists exploiting the situation and trying to make it sound like a conspiracy.

Let the wheels of science grind away. These questions can all be answered. We need to ask all the questions, in proper order, step by step to see if these clusters are real, if so are they genetic or environmental, and if they are environmental what is the trigger.

What we don’t need are people with an agenda politicizing this issue.

No matter what the truth turns out to be, this is likely to be an interesting story and we are likely to learn something about autism.

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