Cernunnos-XLF deficiency is a rare NHEJ1-related syndromic primary immunodeficiency characterized by defective nonhomologous end joining, radiosensitive combined immunodeficiency, microcephaly, and marked growth retardation. Available evidence supports an NHEJ1-driven DNA double-strand break repair defect with downstream failure of V(D)J recombination and developmental tissue maintenance.
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Conditions with similar clinical presentations that must be differentiated from Cernunnos-XLF deficiency:
name: Cernunnos-XLF deficiency
creation_date: "2026-04-15T15:45:03Z"
updated_date: "2026-05-05T00:00:00Z"
description: >-
Cernunnos-XLF deficiency is a rare NHEJ1-related syndromic primary
immunodeficiency characterized by defective nonhomologous end joining,
radiosensitive combined immunodeficiency, microcephaly, and marked growth
retardation. Available evidence supports an NHEJ1-driven DNA double-strand
break repair defect with downstream failure of V(D)J recombination and
developmental tissue maintenance.
category: Mendelian
parents:
- hereditary disease
- primary immunodeficiency
disease_term:
preferred_term: Cernunnos-XLF deficiency
term:
id: MONDO:0012650
label: Cernunnos-XLF deficiency
inheritance:
- name: Autosomal recessive inheritance
description: >-
Cernunnos-XLF deficiency is typically caused by biallelic NHEJ1 variants
segregating in an autosomal recessive pattern.
inheritance_term:
preferred_term: Autosomal recessive inheritance
term:
id: HP:0000007
label: Autosomal recessive inheritance
evidence:
- reference: PMID:28741180
reference_title: "Loss of NHEJ1 Protein Due to a Novel Splice Site Mutation in a Family Presenting with Combined Immunodeficiency, Microcephaly, and Growth Retardation and Literature Review."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Patients were found to have a homozygous splice site mutation immediately downstream of exon 3 in NHEJ1 (c.390 + 1G > C).
explanation: This supports an autosomal recessive mode of inheritance in Cernunnos-XLF deficiency.
pathophysiology:
- name: NHEJ1-related nonhomologous end joining defect
description: >-
Cernunnos-XLF deficiency results from NHEJ1 dysfunction within the
nonhomologous end joining DNA repair pathway, producing a radiosensitive DNA
repair defect.
genes:
- preferred_term: NHEJ1
term:
id: hgnc:25737
label: NHEJ1
biological_processes:
- preferred_term: double-strand break repair via nonhomologous end joining
modifier: ABNORMAL
term:
id: GO:0006303
label: double-strand break repair via nonhomologous end joining
evidence:
- reference: PMID:24511403
reference_title: "Cernunnos/XLF Deficiency: A Syndromic Primary Immunodeficiency."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Artemis, DNA ligase IV, DNA protein kinase catalytic subunit, and Cernunnos/XLF genes in nonhomologous end joining pathways of DNA repair mechanisms have been identified as responsible for radiosensitive SCID.
explanation: This directly supports defective NHEJ DNA repair as the initiating disease mechanism in Cernunnos-XLF deficiency.
downstream:
- target: Defective V(D)J recombination and lymphocyte development
description: Failed DNA repair disrupts immune receptor rearrangement during lymphocyte maturation.
- target: Developmental growth impairment from DNA repair failure
description: Persistent DNA repair failure contributes to impaired somatic and brain growth.
- name: Defective V(D)J recombination and lymphocyte development
description: >-
NHEJ pathway failure impairs repair of programmed DNA breaks during B-cell
and T-cell development, producing combined immunodeficiency.
cell_types:
- preferred_term: T cell
term:
id: CL:0000084
label: T cell
- preferred_term: B cell
term:
id: CL:0000236
label: B cell
biological_processes:
- preferred_term: V(D)J recombination
modifier: ABNORMAL
term:
id: GO:0033151
label: V(D)J recombination
evidence:
- reference: PMID:26455503
reference_title: "Programmed DNA breaks in lymphoid cells: repair mechanisms and consequences in human disease."
supports: PARTIAL
evidence_source: OTHER
snippet: >-
Here we review the mechanisms that repair programmed DNA lesions that occur during B-cell and T-cell development, as well as human diseases that arise through defects in these pathways.
explanation: This review supports the mechanistic link between NHEJ defects such as XLF deficiency and failed repair of programmed DNA breaks during B-cell and T-cell development.
downstream:
- target: Combined immunodeficiency
description: Failed lymphocyte receptor rearrangement compromises adaptive immune development.
- target: Radiosensitivity
description: Impaired repair of DNA double-strand breaks causes increased sensitivity to ionizing radiation.
- name: Developmental growth impairment from DNA repair failure
description: >-
NHEJ1 deficiency causes a syndromic developmental phenotype with impaired
growth and reduced brain growth in addition to immunodeficiency.
evidence:
- reference: PMID:28741180
reference_title: "Loss of NHEJ1 Protein Due to a Novel Splice Site Mutation in a Family Presenting with Combined Immunodeficiency, Microcephaly, and Growth Retardation and Literature Review."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
PURPOSE: We are reporting the first family from the Arabian Gulf with three siblings presenting with combined immunodeficiency (CID), microcephaly, and growth retardation due to a novel NHEJ1 splice site mutation, in addition to a review of the previously published literature on this subject.
explanation: This directly supports a distinct developmental-growth arm downstream of NHEJ1 deficiency.
downstream:
- target: Microcephaly
description: Developmental DNA repair failure contributes to impaired brain growth.
- target: Growth delay
description: Systemic developmental impairment contributes to severe growth retardation.
phenotypes:
- name: Combined immunodeficiency
category: Immunologic
diagnostic: true
description: Combined immunodeficiency is a central clinical manifestation of Cernunnos-XLF deficiency.
phenotype_term:
preferred_term: Combined immunodeficiency
term:
id: HP:0005387
label: Combined immunodeficiency
evidence:
- reference: PMID:28741180
reference_title: "Loss of NHEJ1 Protein Due to a Novel Splice Site Mutation in a Family Presenting with Combined Immunodeficiency, Microcephaly, and Growth Retardation and Literature Review."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
PURPOSE: We are reporting the first family from the Arabian Gulf with three siblings presenting with combined immunodeficiency (CID), microcephaly, and growth retardation due to a novel NHEJ1 splice site mutation, in addition to a review of the previously published literature on this subject.
explanation: This directly supports combined immunodeficiency as a core phenotype of NHEJ1-related Cernunnos-XLF deficiency.
- name: Radiosensitivity
category: Constitutional
description: Radiosensitivity is a cardinal feature of Cernunnos-XLF deficiency.
phenotype_term:
preferred_term: Radiosensitivity
term:
id: HP:0011133
label: Increased sensitivity to ionizing radiation
evidence:
- reference: PMID:24511403
reference_title: "Cernunnos/XLF Deficiency: A Syndromic Primary Immunodeficiency."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Artemis, DNA ligase IV, DNA protein kinase catalytic subunit, and Cernunnos/XLF genes in nonhomologous end joining pathways of DNA repair mechanisms have been identified as responsible for radiosensitive SCID.
explanation: This directly supports radiosensitivity as a defining feature of Cernunnos-XLF deficiency.
- name: Microcephaly
category: Neurologic
diagnostic: true
description: Microcephaly is a recurring syndromic feature in Cernunnos-XLF deficiency.
phenotype_term:
preferred_term: Microcephaly
term:
id: HP:0000252
label: Microcephaly
evidence:
- reference: PMID:24511403
reference_title: "Cernunnos/XLF Deficiency: A Syndromic Primary Immunodeficiency."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
In conclusion, the patients with microcephaly, bird-like face, and severe growth retardation should be evaluated for hypogammaglobulinemia and primary immunodeficiency diseases.
explanation: This directly supports microcephaly as a characteristic syndrome feature.
- name: Growth delay
category: Growth
diagnostic: true
description: Severe growth retardation is part of the syndromic phenotype.
phenotype_term:
preferred_term: Growth delay
term:
id: HP:0001510
label: Growth delay
evidence:
- reference: PMID:28741180
reference_title: "Loss of NHEJ1 Protein Due to a Novel Splice Site Mutation in a Family Presenting with Combined Immunodeficiency, Microcephaly, and Growth Retardation and Literature Review."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
PURPOSE: We are reporting the first family from the Arabian Gulf with three siblings presenting with combined immunodeficiency (CID), microcephaly, and growth retardation due to a novel NHEJ1 splice site mutation, in addition to a review of the previously published literature on this subject.
explanation: This directly supports growth retardation as a core feature of the disease.
biochemical: []
genetic:
- name: NHEJ1
association: Causal loss-of-function variant
gene_term:
preferred_term: NHEJ1
term:
id: hgnc:25737
label: NHEJ1
notes: >-
Cernunnos-XLF deficiency is caused by pathogenic NHEJ1 variants that can
abolish detectable NHEJ1 protein and are typically inherited in an
autosomal recessive pattern.
evidence:
- reference: PMID:28741180
reference_title: "Loss of NHEJ1 Protein Due to a Novel Splice Site Mutation in a Family Presenting with Combined Immunodeficiency, Microcephaly, and Growth Retardation and Literature Review."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Patients were found to have a homozygous splice site mutation immediately downstream of exon 3 in NHEJ1 (c.390 + 1G > C).
explanation: This directly supports NHEJ1 as the causal gene in Cernunnos-XLF deficiency.
- reference: CGGV:assertion_765b118e-c60a-4696-b401-f63b3349d6d2-2021-05-20T151233.276Z
reference_title: "NHEJ1 / Cernunnos-XLF deficiency (Definitive)"
supports: SUPPORT
evidence_source: OTHER
snippet: "NHEJ1 | HGNC:25737 | Cernunnos-XLF deficiency | MONDO:0012650 | AR | Definitive"
explanation: ClinGen classifies the NHEJ1-Cernunnos-XLF deficiency gene-disease relationship as definitive with autosomal recessive inheritance.
environmental: []
treatments:
- name: Hematopoietic stem cell transplantation
description: Hematopoietic stem cell transplantation can provide curative treatment for the severe immunodeficiency component of the disease.
treatment_term:
preferred_term: hematopoietic stem cell transplantation
term:
id: MAXO:0000747
label: hematopoietic stem cell transplantation
target_phenotypes:
- preferred_term: Combined immunodeficiency
term:
id: HP:0005387
label: Combined immunodeficiency
evidence:
- reference: PMID:21535335
reference_title: Two SCID cases with Cernunnos-XLF deficiency successfully treated by hematopoietic stem cell transplantation.
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
These patients received hematopoietic stem cells from HLA identical related donor without conditioning regimen and recovered without any complication.
explanation: This directly supports hematopoietic stem cell transplantation as an effective treatment option.
- name: Immunoglobulin replacement therapy
description: Regular IVIG prophylaxis can reduce infection burden in affected individuals with antibody deficiency.
treatment_term:
preferred_term: Intravenous Immunoglobulin Therapy
term:
id: NCIT:C121331
label: Intravenous Immunoglobulin Therapy
therapeutic_agent:
- preferred_term: human immunoglobulin G
term:
id: NCIT:C80829
label: Human Immunoglobulin G
target_phenotypes:
- preferred_term: Combined immunodeficiency
term:
id: HP:0005387
label: Combined immunodeficiency
evidence:
- reference: PMID:24511403
reference_title: "Cernunnos/XLF Deficiency: A Syndromic Primary Immunodeficiency."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
She is now on regular IVIG prophylaxis and has no new infection.
explanation: This directly supports immunoglobulin replacement as a supportive treatment for the immune phenotype.
diagnosis:
- name: NHEJ1 molecular genetic testing
description: Molecular testing for pathogenic NHEJ1 variants confirms the diagnosis in patients with the characteristic syndromic immunodeficiency phenotype.
presence: Screening for NHEJ1 mutations is indicated in the syndromic CID phenotype.
diagnosis_term:
preferred_term: molecular genetic testing
term:
id: MAXO:0000533
label: molecular genetic testing
qualifiers:
- predicate:
preferred_term: has participant
term:
id: RO:0000057
label: has participant
value:
preferred_term: NHEJ1
term:
id: hgnc:25737
label: NHEJ1
evidence:
- reference: PMID:28741180
reference_title: "Loss of NHEJ1 Protein Due to a Novel Splice Site Mutation in a Family Presenting with Combined Immunodeficiency, Microcephaly, and Growth Retardation and Literature Review."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
CONCLUSION: Patients presenting with CID, microcephaly, and growth retardation should be screened for NHEJ1 gene mutations.
explanation: This directly supports NHEJ1 molecular testing as the key confirmatory diagnostic procedure.
differential_diagnoses:
- name: Fanconi anemia
description: Fanconi anemia can be considered because of growth failure and chromosomal breakage.
distinguishing_features:
- A normal DEB test argues against Fanconi anemia.
- Hypogammaglobulinemia and combined immunodeficiency favor Cernunnos-XLF deficiency.
disease_term:
preferred_term: Fanconi anemia
term:
id: MONDO:0019391
label: Fanconi anemia
evidence:
- reference: PMID:24511403
reference_title: "Cernunnos/XLF Deficiency: A Syndromic Primary Immunodeficiency."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Firstly, she was thought as Fanconi anemia and spontaneous DNA breaks were seen on chromosomal analysis. After that DEB test was found to be normal and Fanconi anemia was excluded.
explanation: This directly supports Fanconi anemia as an important early differential diagnosis.
- name: Nijmegen breakage syndrome
description: Nijmegen breakage syndrome overlaps through microcephaly, growth failure, and immunodeficiency.
distinguishing_features:
- Absence of NBS1 pathogenic variants argues against Nijmegen breakage syndrome.
- Identification of a causal NHEJ1 variant supports Cernunnos-XLF deficiency.
disease_term:
preferred_term: Nijmegen breakage syndrome
term:
id: MONDO:0009623
label: Nijmegen breakage syndrome
evidence:
- reference: PMID:24511403
reference_title: "Cernunnos/XLF Deficiency: A Syndromic Primary Immunodeficiency."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: >-
Because of that she had low IgG and IgA levels, normal IgM level, and absence of B cells in peripheral blood; she was considered as primary immunodeficiency, Nijmegen breakage syndrome. A mutation in NBS1 gene was not found; then Cernunnos/XLF deficiency was investigated due to clinical similarities with previously reported cases.
explanation: This directly supports Nijmegen breakage syndrome as a clinically relevant differential diagnosis.
clinical_trials: []
datasets: []
notes: >-
Asta deep research was completed for this disorder. Final curation emphasized
disease-specific human case and review literature with direct abstract support.
This report is retrieval-only and is generated directly from Asta results.
search_papers_by_relevance with snippet_search.