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Table 2A. Primary Immune Deficiency Treatment
Consortium (PIDTC) 2022 Definitions for SCID
SCID
Subtype Criterion 1
Criterion
2 Criterion 3 Criterion 4
Typical
SCID
Very low T cells
(<0.05 × 10
3
/L)
Pathogenic
variant in
SCID-
associated
gene
No alternate
explanation
for low
T-cell count
and either:
Undetectable
or low TREC
or <20%
naive CD4 T
cells
Presence of maternal
T-cell engrament
Criteria 1
and 2 OR
criteria 1
and 3 OR
criterion 4
Leaky/
atypical
SCID
Two or more of:
• Low T-cell
number for age
• Oligoclonal T
cells
• Abnormal
TREC OR
<20% naive
CD4 T cells
Pathogenic
variant in
SCID-
associated
gene
Reduced
T-cell
proliferation
Does not have:
• Other SCID
subtype
• Combined
immunodeficiency
(CID) with known
phenotype
• Thymic disorder
• Other disorder
with low T-cell
number
Criteria 1
and 2 and 4
OR criteria
1 and 3
and 4
Omenn
syndrome
All 4 criteria
>80% of CD4
cells have
CD45RO
memory
phenotype
Pathogenic
variant in
SCID-
associated
gene
Generalized
rash and
absence of
maternal
T-cell
engrament
Two or more of:
• Eosinophilia
• Elevated IgE level
• Abnormal TREC
• Lymphadenopathy
• Hepatomegaly and/
or splenomegaly
• Oligoclonal T cells
