Methemoglobinemia

I've always found the science of blood to be interesting, so for my first entry I decided to pick a blood disorder: Methemoglobinemia. That's pronounced, met·he·mo·glo·bi·ne·mi·a. Methemoglobinemia, aside from being a really neat word, is a blood disorder characterized by abnormally high levels of methemoglobin in the blood. Methemoglobin doesn't bind oxygen like normal hemoglobin does, thus tissues are deprived of oxygen. This lack of oxygen (tissue hypoxia) results in a markedly blue tint in individuals suffering from the disorder, thus the disorder's more commonly known name: blue skin disorder. This isn't nearly as sexy as Avatar would make it seem. Think more like, Violet Beauregarde from Willy Wonka and the chocolate factory. While not nearly as puffy, people with Methemoglobinemia often have blueberry-colored skin. 

So how does one get Methemoglobinemia? There are two ways: congenital and acquired. Congenital meaning you are born with it, and acquired mean you were unfortunate enough to get it all on your own. 


Those with congenital Methemoglobinemia, which I will henceforth abbreviate as met-Hb because I'm tired of staring at the long red scribbles on my computer screen, have a deficiency of diaphorase I. This is the enzyme responsible for converting methemoglobin to hemoglobin. Normal hemoglobin is red in color, whereas methemoglobin has brown tint. For people with lighter skin, this results in a blueish hue. There are a few other congenital causes involving hemoglobin malformations and other enzyme deficiencies, but this is probably the greatest congenital factor.


Let's take a quick look at the difference between a red blood cell (erythrocyte) with hemoglobin and a red blood cell with methemoglobin.

A molecule of hemoglobin has for subunits (two beta and two alpha) each with a heme group containing a ferrous iron molecule. Ferrous iron has a 2+ charge. In methemoglobin, the iron molecule is in its ferric state with a 3+ charge, making it unable to bind and transport oxygen. Now the illustration of the two erythrocytes is an exaggeration. You usually won't have a red blood cell composed entirely of one type of hemoglobin, as there are around 270 million hemoglobin molecules per red blood cell. Even a healthy individual will possess methemoglobin, though it is in levels below 1%. 


So for people with met-Hb, this disorder is caused by an autosomal recessive gene. Here's what that looks like in stick figure form.The "b" denotes the gene coding for the disorder, while the "B" denotes a healthy gene. (Also note that blue people aren't necessarily blue-skinned, they're just boys). Since it's recessive, the defective gene must be passed from both parents for the child to be affected by the disorder. Thusly, people can be carriers for the disorder without being affected by it themselves. 

Probably the most famous case of met-Hb is the Fugate family from the hills of Kentucky. I remember when I went to middle school in Frankfurt, KY, we had a reading prompt about them. In short, Mr. Fugate married Mrs. Fugate who was a carrier for the disorder. They intermarried with a nearby clan in the 1800's and bam, later generations of Fugate babies were blue. Probably the fastest way to cultivate recessive disorders is through inbreeding. From what I understand, it's why dalmatians are so screwy. 


Acquired met-Hb can be caused by a number of outside sources. Oxidizing drugs such as benzocaine (a topical anesthetic) and certain antibiotics, can interrupt the natural, protective enzyme pathway in blood, causing a large increase in the amount of methemoglobin. Nitrate compounds can also be a causative factor. In babies, nitrates consumed from drinking water can cause met-Hb, or blue-baby syndrome.


Luckily, for those unfortunate enough to resemble real-life smurfs, there are treatments for the disorder. The disorder can be treated with supplemental oxygen and methylene blue. Methylene blue is administered either intravenously or orally. It acts to restore ferrous iron to the blood, restoring its ability to bind oxygen.


So that was a lot longer than I anticipated it being, but I think I covered a decent amount of information. Hope you all learned something interesting.