Down Syndrome Abstract
of the Month: March 1999

Abstract:

Cow's milk protein intolerance (CMPI) is the most frequent food intolerance in infancy. Its incidence ranges from 0.3 to 7.5%, according to different diagnostic criteria and clinical features. The diagnosis of CMPI is generally based on the level of IgG antibodies to beta-lactoglobulin. An association of insulin-dependent diabetes millitus (IDDM) with CMPI has been reported. CMPI in subjects with Down syndrome (DS) has been investigated by Nespoli et al and Reicht et al. We assayed IgG antibodies to beta-lactoglobulin by the ELISA method in 78 subjects with DS and 97 mentally retarded and home reared control subjects. Gastrointestinal disorders and IDDM was ruled out in both groups. Eleven (14.1%) and 5 (5.1%) subjects among DS group and control group respectively were put on a CMP-free diet and showed relief of symptoms and normalization of antibodies after 6 to 21 months. In conclusion, CMPI appears to be more frequent in DS versus the control group and the specificity of IgG antibodies approaches 100% in our study.
 

My comments:

First, a quick immunologic primer. Immunoglobulins (Ig), also called antibodies, make up the "humoral" immune system (as opposed to the cellular immune system, which includes white blood cells). Ig identification of "foreign" proteins starts a process in which the foreign protein is removed from the body. You can put the Ig into different groups: IgA, IgG, IgM, IgD and IgE. IgE is the Ig responsible for causing allergic symptoms, such as wheezing, coughing, runny noses and hives. If the IgE in the intestinal lining is stimulated, you can also get the symptoms of cramping, gas, diarrhea and vomiting.

Food proteins can be "antigens" (foreign proteins), in that they can stimulate the production of immunoglobulins. When a protein does produce such an effect, it's called an allergy or a protein intolerance. (Some scientists call all food reactions "intolerance," and some reserve the term for non-allergic food reactions. The authors of this study use it interchangably with allergy.) As I mention above, IgE is primarily responsible. The role of other immunoglobulins in protein intolerance is speculative, but IgM and IgG have been implicated. In cow's milk, the whey protein beta-lactoglobulin is the most allergenic protein.

Usually, lab testing for food allergies involves looking for signs of Ig involvement: like IgG directed against lactoglobulin. Most types of blood testing for food allergies have been unreliable. Specifically, attempts to try to identify allergies through IgG assays have been fairly disappointing, and appear to be measures of exposure. So, decreasing levels of IgG would correspond to decreased exposure to the cow's milk protein. I did not have high hopes for this article based on that.

The authors state that the diagnosis of CMPI was made at the beginning of the study before any tests were done. They do not tell us what their criteria were for making this diagnosis. They do say that the symptoms went away after the subjects were placed on a cow's milk protein-free diet, which is the best standard yet for checking for the presence of an allergy.

The bottom line is that in children with DS with symptoms of chronic allergies, a milk-free trial may be helpful in determining the cause of the allergies.

Addendum, June 2005: A new blood test is now available for testing for food allergies and measures the IgE levels. This blood test is still not quite as accurate as the skin test, but is a much more reliable indicator than the old IgG.