Hi, this is Tom, and in this episode I'm going to be going through severe combined

immunodeficiency. And you can find notes at zero to finals.com and in the zero to finals

pediatrics book. And you can find flashcards and questions to train your knowledge at members.0.0.5.com.

So let's jump straight in.

Severe combined immunodeficiency, shortened to Skid, is the most severe primary immunodeficiency disorder.

Patients with Skid have almost no immunity to infections. It may be caused by a number

of different genetic abnormalities that result in absent or dysfunctional T cells and impaired B-cell

function. Let's talk about the presentation. Severe combined immunodeficiency typically presents

in the first few months of life with persistent severe diarrhea, failure to thrive, frequent and

severe infections, for example severe candidacysus, severe chicken pox, or pneumocysticegevecone, pneumonia,

illness following live vaccines, for example the BCG vaccine for tuberculosis and the MMR vaccine,

and Omen syndrome, which we're going to talk about in more detail shortly.

Let's talk about the causes.

Over 50% of cases are caused by mutation in a gene on the X chromosome

that encodes for the common gamma chain.

This common gamma chain is a shared subunit of various interleukin

receptors. This means that if there's a problem with the common gamma chain, then various

interleukin receptors will be malfunctional. This results in absent T cells and absent natural killer cells and non-functioning B cells.

This type of severe combined immunodeficiency has X-linked recessive inheritance,

which means it almost exclusively affects males.

Other genetic mutations that can lead to severe

combined immunodeficiency include Jack 3 gene mutations and mutations leading to

...