Saturday, 19 March 2011

Enzyme activity, milk and autism

Remember the old Namco classic Pac-Man? That yellow circular pixelated fellow running around a maze gobbling up dots and the odd power pellet making him invulnerable to the ghosts. I must have spent days of my life playing that game as a child (yeah.. er, as a child).

Pac-Man is not a bad metaphor for our gastrointestinal enzymes and the job they do gobbling up various proteins, peptides and sugars derived from our diet and spitting them out into their constituent parts for more manageable digestion, absorption and use. OK such enzymes don't look like Pac-Man and they don't exactly just gobble up and spit out dots; just a little creative flair on my part to save a long laborious biochemistry lesson.

There is quite a bit of evidence to suggest that gut enzyme function in some cases of autism is perhaps not what it should be. The various -ases (proteases / peptidases, disaccharidases) have all pretty much come under the spotlight at one time or another in relation to autism. The proposed association between autism and various gastrointestinal conditions and dietary elements have brought some enzymes centre-stage as result. A recent paper from Harvard adds to the research evidence. The team, which includes Tim Buie, lead for the recent American Academy of Pediatrics guideline document on autism and gastrointestinal conditions, have published in this area before.

Last time they reported that disaccharidase activity (an enzyme that breaks down two component sugar compounds, disaccharides, into single sugar components, monosaccharide) was looking a little bit shaky in quite a few people with autism. In particular they noted that several dissacharidases were related to specific conditions in autism, including lactase. Lactase is essential for breaking down lactose, the sugar in milk and dairy products.

The more recent paper details similar findings with regards to problems with lactase and suggested that lactose intolerance might be pretty widespread in autism. The authors went on to suggest that this could account for some of the observed abdominal discomfort, pain and 'aberrant behaviour' observed in some cases of autism. I remember quite a while ago Afzal and colleagues reported that milk consumption was one of the primary predicting factors for constipation in autism.

This is an important paper. Not only is it a replication of previous work, it highlights what seems to be a common problem in autism particularly related to milk and dairy products. If I say the words 'casein-free diet and autism' would that perhaps ring any bells? A few words of caution are required. First lactose intolerance can be quite widespread in the general population; the map shown here claims to show population level risk of lactose intolerance. If for example you are Chinese in ethnicity, you have a very high chance of developing lactose intolerance. As with coeliac disease and the Irish population, the theory is that the traditional Chinese diet is probably not as high in milk and dairy products as that of other parts of the world, or incorporates different types of milk sources and hence exposure to lactose is perhaps not as great as in other parts of the world. It's a case of use it or lose it.

Chronological age is also a factor. Babies tend to be better protected against lactose intolerance given that milk (mothers or formula) are a staple foodstuff as such an age. The interesting thing about the recent Harvard paper is that they reported over 50% of children under 5 were showing lactase deficiency. So when the kids needed the enzyme the most it was perhaps not present. Mmm. Reminds me of some of the original cases described by Leo Kanner particularly cases 4, 7, 8, 10 who all experienced early feeding problems. Coincidence?

We have also to think about the old adage 'correlation does not imply causation'. It is possible that such enzyme problems are purely epiphenomenal and unrelated to autism. Possible at least. One final word about the new research. One of the most interesting statements in the Harvard paper is that of the last sentence of the abstract: 'Most autistic children with lactose intolerance are not identified by clinical history'. Meaning that if you don't go looking for it directly, the chances are that problems with the disaccharidases are not going to be picked up by reading a developmental history alone. I guess what this is telling us is that just because a person has an autism spectrum condition, don't assume that they are somehow protected against other conditions. Coeliac disease? Iron deficiency?

Readers of this blog will know that I have some views on the use of gluten- and casein-free diets as a potential tool for ameliorating some core and peripheral symptoms associated with autism. Anything that can help identify that autism 'phenotype' where diet may be related is welcome news.