Definitive

Male or female patient with decreased intensity of expression (less than 5% of normal) of HLA-DR or DP on B cells or monocytes and a mutation in one of the following genes: CIITA, RFX-B, RFX-5 or RFX-AP.

Probable

Male or female patient with decreased intensity of expression (less then 5% of normal) of HLA-DR or DP on B cells and monocytes and all of the following:

1. Failure to thrive, opportunistic infections or persistent viral infections
2. Normal numbers of T cells and B cells
3. Normal proliferative responses to mitogens

Possible

Male or female patient with decreased intensity of expression (less then 5% of normal) of HLA-DR or DP on B cells or monocytes, and normal numbers of T cells and B cells, who has at least one of the following:

1. Hypogammaglobulinemia
2. Normal mitogen responses but absent T cell proliferation to antigens
3. Reduced numbers of CD4+ cells
4. Failure of mononuclear cells to stimulate a mixed lymphocyte culture

Spectrum of disease

MCH Class II deficiency, which is seen most often in patients from around the Mediterranean sea, results in a clinical phenotype that is very similar to SCID. Patients usually develop severe infections and protracted diarrhea in the first 6 months of life. Pseudomonas, CMV and Cryptosporidium infections are common. The four genetic disorders that result in this syndrome are clinically indistinguishable. In most cases, there is no class II expression; however, in others the intensity of expression may be as high as 5% of normal. Patients with higher expression tend to have a milder course; these patients may survive beyond early childhood. Hepatic abnormalities, particularly sclerosing cholangitis, are frequent.