Hematology

Navigating the Diagnosis and Pathology Reports

At a Glance

JAGN1-SCN is confirmed by combining a child's persistently very low neutrophil counts, bone marrow that stops neutrophil development early, and disease-causing changes in both copies of the JAGN1 gene. Chromosome and acquired marrow-cell mutation tests provide a baseline for follow-up.

Getting to a definitive diagnosis of JAGN1 severe congenital neutropenia (SCN) is a multistep process. It requires looking at the blood, the bone marrow “factory,” and the underlying genetic blueprints. While the symptoms of frequent infections often raise suspicion, the diagnosis is confirmed when clinical, marrow, and genetic puzzle pieces fit together ^[1]^[2].

The Genetic Blueprint: Molecular Testing

A molecular diagnosis of JAGN1-SCN requires finding pathogenic or likely pathogenic variants in the JAGN1 gene, interpreted alongside the patient’s symptoms.

Because this condition is autosomal recessive, a child typically must have biallelic mutations—meaning two changes in the JAGN1 gene, either the same change from both parents (homozygous) or a different change from each parent (compound heterozygous) ^[3]^[4].

While Next-Generation Sequencing (NGS) (like a targeted gene panel or exome sequencing) is often used, a standard panel may sometimes miss deletions, duplications, or deep intronic variants ^[5]. If testing is negative but suspicion is high, further genetic evaluation or copy-number analysis may be needed. A genetic counselor can help guide this process and explain when orthogonal confirmation (a second laboratory method to double-check results) is required.

The Bone Marrow “Factory” Report

To see why the body isn’t making enough neutrophils, doctors perform a bone marrow aspirate and biopsy. In JAGN1-SCN, a classic finding is granulocytic maturation arrest ^[6].

Think of the bone marrow as an assembly line. In a healthy child, you would see cells at every stage of development, from “babies” to “adults.” In a child with JAGN1-SCN, the assembly line stops partway through. You will see plenty of early cells (called promyelocytes or myelocytes), but very few or no mature neutrophils ^[7]^[8]. This “arrest” is the biological reason why the neutrophil count in the blood remains so low ^[9].

Somatic Mutations: The Baseline Safety Check

At the time of diagnosis, your doctor may also look for somatic mutations. These are genetic changes that are not inherited but happen spontaneously within the bone marrow cells over time ^[10].

The two most common markers to watch are CSF3R and RUNX1 ^[11]. While many children with SCN carry small “clones” of cells with these mutations without any problems, they can sometimes be an early warning sign of myelodysplastic syndrome (MDS) or leukemia later in life ^[12]^[2]. Checking for them at the very beginning creates a “baseline” so your team can monitor any changes in future years, though the results require expert interpretation ^[13].

Completeness Checklist for Parents

When you receive your child’s diagnostic folder, these are the components clinicians may use to thoroughly evaluate the condition:

Serial CBCs: Blood counts showing an Absolute Neutrophil Count (ANC) consistently below 0.5 × 10⁹/L ^[14]^[1].
Bone Marrow Morphology: A report describing the stage of “maturation arrest” and noting the percentage of blasts (immature blood-forming cells). Note that an increased blast percentage can be concerning, but blasts are not automatically “cancer” ^[2]^[7].
Cytogenetics (Karyotype/FISH): A test to ensure the chromosomes in the bone marrow cells are structurally normal (e.g., checking for “Monosomy 7”) ^[2]^[15].
Biallelic JAGN1 Finding: A genetic report identifying pathogenic changes in the JAGN1 gene ^[3].
Somatic Panel: Results for baseline CSF3R and RUNX1 mutation status ^[11]^[10].
Immunological Workup: Tests for immunoglobulin levels (IgG, IgA, IgM) and lymphocyte counts to see if other parts of the immune system are affected ^[16]^[17].

Common questions in this guide

What genetic findings support a diagnosis of JAGN1-SCN?

The diagnosis is supported by a pathogenic or likely pathogenic change in both copies of the JAGN1 gene, along with compatible clinical findings. The two changes may be identical, or one may be inherited from each parent; parental testing can help confirm this pattern.

What does maturation arrest mean in a bone marrow report?

It means neutrophil development has stopped before the cells become mature. In JAGN1-SCN, the marrow may contain many early cells such as promyelocytes or myelocytes but few or no mature neutrophils, helping explain the low blood count.

Can a standard genetic panel miss JAGN1 deficiency?

Yes. Some sequencing panels may not detect deletions, duplications, or changes in parts of the gene that are harder to analyze. If suspicion remains high after a negative result, clinicians may consider copy-number testing or another genetic method with help from a genetic counselor.

Why are CSF3R and RUNX1 checked at diagnosis?

These tests look for changes that arise in bone marrow cells rather than being inherited. Small groups of cells with these changes may occur without causing problems, but they can sometimes be an early warning sign of myelodysplastic syndrome or leukemia, so an initial result provides a baseline for monitoring. A positive result does not by itself mean that the child has cancer.

What tests are included in a complete JAGN1-SCN evaluation?

Clinicians may review repeated blood counts and ANC values, bone marrow morphology and blast percentage, chromosome testing, the JAGN1 genetic report, and a baseline CSF3R and RUNX1 panel. They may also check immunoglobulin levels and lymphocyte counts to see whether other parts of the immune system are affected.

Why does the care team need to know whether the marrow sample was taken before G-CSF?

The timing of the bone marrow sample in relation to G-CSF treatment is important context when clinicians interpret the report. Tell the team whether treatment had started and share the full report so they can assess the findings accurately.

Get notified when new evidence is published on Severe congenital neutropenia due to JAGN1 deficiency.

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This page is for informational purposes only and does not constitute medical advice. A pediatric hematologist, genetic counselor, or pathologist should interpret your child's JAGN1-SCN results and recommend next steps.