A quick lesson in blood cells, ADA and SCID

I thought now would be a good time to tell you all about the various types of blood cells we have in our blood.

Bone Marrow - this is the source of our immune cells. Ella's bone marrow will gradually overtake Harrison's, and the ideal result will be he produces white cells that have ADA enzyme. Ella only has a 0.5 count which is slightly below normal range of (0.6 - 1.6) - but even a small amount of enzyme will give Harrison immunity.

ADA Enzyme - this is the enzyme present in the blood, and is vitally important for cellular function and metabolism. Without it toxins build up in the lymphocytes causing them to die off - thus no immunity. It is also an enzyme that is important for brain metabolic function.

T-lymphocytes and B-lymphocytes. T-lymphocytes are matured in the Thymus Gland (Harrison's thymus is not evident on the chest x-rays he has had) and go around fighting different viruses. The B-lymphocytes are further defined into different cells called immunoglobulins. These are antibodies and fight infection. Everyone has many different types of immunoglobulins to fight different types of infections. Namely IgG, IgA, IgM and IgE - plus a couple others. Harrison has a small amount of IgM, but not A or G - so the IVIG (Intragam) infusion replaces these for now.

Without ADA a child then develops SCID. SCID means Severe Combined Immune Deficient. What this means is that Harrison has hardly any T or B-lymphocytes (white blood cells) and as a result can not fight any virus or bacteria that comes his way. Isolation was the key to keeping Harrison well. No contact with the outside world kept him well enough to undergo BMT.

Due to this being a metabolic problem as much as it is SCID, Harrison has toxins in his body that can inhibit his organs and because of this it is one of the more troublesome types of SCIDs.

ADA is a very rare genetic disorder. It is autosomal recessive meaning that as his parents, Scott and I carry the gene that causes ADA and we both pass on this recessive gene causing Harrison to be ADA deficient. I previously outlined statistics, but the statistics for baby to be born with with ADA is one child in every two million(based on figures from the USA). Australian population is considerably smaller than the US and Canada, and we have only ever had three or four cases of ADA deficiency diagnosed in Australia. The exact number is hard to track down as Harrison is the only one on the PID register (Primary Immune Deficiency). The chances that we will have a child with ADA is one in four. The chances of a child that is NOT a carrier or affected is also one in four. and to have kids who are carriers is a one in two chance.

As it turns out we fit the scientific model nicely.
Child 1 - Not a carrier and not affected - Marlie
Child 2 and 3 - Carrier but not affected - Sterling and Ella
Child 4 - Affected - Harrison.

Of course not all families work this way - some families have a number of children affected. We were just lucky. We were also offered genetic counselling and offered testing so that if we were to have more children then we could go through IVF and have a baby not affected.

Given Harrison is our definite last child we won't need to go through all of that, but I can certainly understand what it will take for a family that will.