Hello and welcome to the Zero Definals podcast. My name is Tom and in this episode I'm going to be

talking to you about severe combined immunodeficiency. If you want to follow along with written

notes on this topic, you can follow along at zero definals.com slash skid, or in the immunology section of the Zero-definals paediatrics book.

So let's get straight into it.

Severe combined immunodeficiency, often abbreviated to Skid, is the most severe condition

causing immunodeficiency.

Children with Skid have almost no immunity to infections.

It's a syndrome caused by a number of different genetic disorders that result in

absent or dysfunctioning T and B cells. So how does it present? Skid will present in the

first few months of life with persistent severe

diarrhea, failure to thrive, opportunistic infections that are more frequent or severe than in

healthy children, for example severe and later fatal chicken pox, numocysis deovecineumonia and

cytomegalovirus.

Patients can be unwell after live vaccinations such as the BCG, MMR or the nasal flu vaccine,

and Omen syndrome, which we'll talk about more in detail later.

Let's talk more about the causes.

More than 50% of cases are caused by a mutation in the common gamma chain on the X chromosome that codes for interleukin receptors on T and B cells.

This has X-linked recessive inheritance. There are many other gene mutations that can lead to Skid, including Jack 3 gene

mutations and mutations leading to adenosine deaminase deficiency. Let's talk in more detail

about Omen syndrome. Omen syndrome is a rare cause of skid. It's a result of a mutation in the recombination

activating gene, Ragh 1 or Rag 2, that codes for important proteins in the T and B cells.

It has autosomal recessive inheritance.

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