Clinical Immunology

The Path to Diagnosis: Genes and Lab Tests

At a Glance

Doctors diagnose STK4 deficiency by combining immune blood tests, such as CD4 counts and vaccine-response testing, with genetic testing. Confirmation usually requires harmful changes in both STK4 gene copies; protein testing may help when results are uncertain.

The journey to a diagnosis for STK4 deficiency often begins with a series of blood tests that reveal a struggling immune system, but the definitive answer requires genetic testing combined with clinical evaluation. Because this condition shares many symptoms with other rare diseases, doctors must evaluate the full clinical picture to confirm STK4 deficiency ^[1]^[2].

The Diagnostic Puzzle: Laboratory Clues

A diagnosis typically starts when an immunologist notices specific patterns in blood work. While no single lab value “proves” the disease, several findings together point toward it. It’s important to note that these are observations from small cohorts and must be interpreted using age-adjusted reference ranges:

CD4 Lymphopenia: A hallmark of the disease. In a small published cohort of 9 patients, all had low counts of CD4 T cells, which are the vital “helper” cells of the immune system ^[1].
Altered T Cell Subsets: The body may show decreased “naive” T cells (cells ready to fight new infections) and increased “effector-memory” T cells ^[1]^[3].
Variable Immunoglobulins: Overall immunoglobulin (antibody) levels are highly variable. Many patients have normal or even high levels of IgG or IgA ^[1]. However, some have low IgM and high IgE ^[1]^[4].
Poor Vaccine Response: Even if total antibody levels look normal, functional testing might show those antibodies don’t work correctly. Doctors check vaccine titers (measuring immunity after a vaccine like tetanus or diphtheria). Responses in STK4 deficiency are variable; some patients have insufficient responses while others maintain detectable specific antibodies ^[1]^[2].

Why Genetic Testing is Necessary

Because laboratory findings can vary, genetic testing is required to confirm STK4 deficiency. This usually involves:

Whole Exome Sequencing (WES) or Whole Genome Sequencing (WGS): These advanced tests scan the DNA to look for pathogenic variants in the STK4 gene ^[2]^[4].
Variant Confirmation: The laboratory must confirm that there are two pathogenic (or likely pathogenic) variants (biallelic) and that they are “in trans” (one on each chromosome). While Sanger sequencing is sometimes used to confirm WES findings or test parents, laboratories may use other appropriate methods. A “Variant of Uncertain Significance” (VUS) is not a definitive diagnosis without further functional or segregation studies ^[5]^[2].
Protein Studies: In cases where the genetic result is uncertain, doctors may perform an immunoblot to see if the MST1 protein is absent or reduced in the cells ^[6]^[4].

The “Look-Alikes”

STK4 deficiency can look very similar to other rare immune disorders, requiring specialist evaluation:

DOCK8 Deficiency: Both can cause high IgE, eczema, and low CD4 counts. However, DOCK8 often involves more severe food allergies and specific severe viral skin infections ^[1]^[7].
ALPS (Autoimmune Lymphoproliferative Syndrome): Both can present with an enlarged spleen and swollen lymph nodes. While STK4 deficiency lacks typical ALPS-associated Fas pathway mutations, ALPS can sometimes be diagnosed clinically without an identifiable mutation, so careful immunologic and genetic evaluation is required to distinguish them ^[8].

How It Is Inherited

STK4 deficiency is an autosomal recessive condition. This means a person must inherit two mutated copies of the gene—one from each parent—to have the disease ^[1]^[5].

Carriers: Parents are typically “carriers.” They have one functional gene and one mutated gene, and usually have no symptoms ^[2]^[5].
The 25% Rule: When two carriers have a child, there is a 25% chance with each pregnancy that the child will have STK4 deficiency, a 50% chance the child will be a carrier, and a 25% chance the child will not have the mutation at all ^[2].

Genetic counseling is highly recommended for families to understand these risks, discuss testing for siblings or other relatives, and assist with reproductive planning ^[2].

Your Diagnostic Checklist

When reviewing lab reports with your specialist, consider asking about these key items:

[ ] Absolute CD4 Count: Is it low for age?
[ ] Lymphocyte Subsets: Specifically, what are the naive vs. memory T cell counts?
[ ] Vaccine Titers: Was there a functional response to previous vaccines?
[ ] STK4 Mutation Status: Does the report confirm two pathogenic or likely pathogenic variants that are in trans?
[ ] Carrier Testing: Has testing been offered to confirm carrier status of the parents?

Common questions in this guide

Which lab results can point to STK4 deficiency?

Doctors may look for a low CD4 T-cell count, fewer naive T cells that are prepared to respond to new infections, more effector-memory T cells, and variable antibody levels. These findings can support the diagnosis, but they are not specific by themselves and must be interpreted using age-adjusted ranges.

What genetic result confirms STK4 deficiency?

Confirmation usually requires two pathogenic or likely pathogenic changes in the STK4 gene, with one on each chromosome, a pattern called being in trans. Whole exome or whole genome sequencing may find the changes, but a variant of uncertain significance alone does not establish the diagnosis.

Can normal antibody levels rule out STK4 deficiency?

No. IgG and IgA may be normal or high, so doctors may also measure vaccine titers to see whether antibodies work after vaccines such as tetanus or diphtheria. Responses can vary among people with STK4 deficiency.

What does “in trans” mean in an STK4 test?

It means the two STK4 variants are on opposite copies of the gene, one on each chromosome. This arrangement is important for an autosomal recessive diagnosis and may require testing the parents or additional laboratory review to confirm.

How do doctors tell STK4 deficiency apart from DOCK8 deficiency or ALPS?

Doctors compare the person's infection history, immune-cell and antibody results, and genetic findings. DOCK8 deficiency may be associated with severe viral skin infections and food allergies, while ALPS is evaluated using spleen or lymph-node findings and the Fas pathway; specialist assessment is needed because the conditions can overlap.

What are the chances of passing STK4 deficiency to a child?

STK4 deficiency is autosomal recessive, so a child generally needs one altered gene copy from each parent. When both parents are carriers, each pregnancy has a 25% chance of the child having the condition, a 50% chance of being a carrier, and a 25% chance of inheriting neither altered copy.

When are MST1 protein studies used?

If genetic testing does not give a clear answer, an immunoblot may measure MST1 protein in cells. An absent or reduced amount can provide supporting evidence, but the result is interpreted together with clinical findings and genetic testing.

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References (8)

1
Diversity in Serine/Threonine Protein Kinase-4 Deficiency and Review of the Literature.
Cagdas D, Halacli SO, Tan C, et al.
The journal of allergy and clinical immunology. In practice 2021; (9(10)):3752-3766.e4 doi:10.1016/j.jaip.2021.05.032.
PMID: 34146746
2
Serine/Threonine Kinase 4 Deficiency Caused by a Potential Novel c.248del, p.Pro83Leufs∗3 Mutation: A Case Report.
Ashayeri H, Eskandarzadeh S, Alavi S, et al.
Case reports in immunology 2026; (2026()):8573882 doi:10.1155/crii/8573882.
PMID: 42602440
3
Epidermodysplasia Verruciformis and Vδ2 γδ T-cell Expansion in STK4 Deficiency.
Ying W, Long X, Vandergriff T, et al.
Journal of clinical immunology 2024; (44(8)):172 doi:10.1007/s10875-024-01780-z.
PMID: 39110273
4
A Novel STK4 Mutation Impairs T Cell Immunity Through Dysregulation of Cytokine-Induced Adhesion and Chemotaxis Genes.
Guennoun A, Bougarn S, Khan T, et al.
Journal of clinical immunology 2021; (41(8)):1839-1852 doi:10.1007/s10875-021-01115-2.
PMID: 34427831
5
A novel mutation in the STK4 gene (Serine/threonine kinase 4) in a Chinese Blang child.
Liu Y, Lei Y, Li M, et al.
Immunology letters 2026; (280()):107182 doi:10.1016/j.imlet.2026.107182.
PMID: 42119789
6
Defective Leukocyte Adhesion and Chemotaxis Contributes to Combined Immunodeficiency in Humans with Autosomal Recessive MST1 Deficiency.
Dang TS, Willet JD, Griffin HR, et al.
Journal of clinical immunology 2016; (36(2)):117-22 doi:10.1007/s10875-016-0232-2.
PMID: 26801501
7
The extended clinical phenotype of 64 patients with dedicator of cytokinesis 8 deficiency.
Engelhardt KR, Gertz ME, Keles S, et al.
The Journal of allergy and clinical immunology 2015; (136(2)):402-12.
PMID: 25724123
8
EBV Negative Lymphoma and Autoimmune Lymphoproliferative Syndrome Like Phenotype Extend the Clinical Spectrum of Primary Immunodeficiency Caused by STK4 Deficiency.
Schipp C, Schlütermann D, Hönscheid A, et al.
Frontiers in immunology 2018; (9()):2400 doi:10.3389/fimmu.2018.02400.
PMID: 30386345

This page is for informational purposes only and does not constitute medical advice about STK4 deficiency. Your immunologist, genetics specialist, and genetic counselor can interpret your results and guide testing for your family.

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