🏷

Classifications

Harrison's Chapter

IUIS Category

👪

Inheritance

1

Autosomal recessive inheritance HP:0000007

NBSLD is caused by biallelic (compound heterozygous or homozygous) hypomorphic RAD50 variants and segregates as an autosomal recessive trait, in parallel with the other two MRN-complex disorders (NBN-related Nijmegen breakage syndrome and MRE11-related ataxia-telangiectasia-like disorder).

Autosomal recessive inheritance

Show evidence (2 references)

PMID:19409520 SUPPORT Human Clinical

"Hypomorphic mutations in NBN (previously known as NBS1) and MRE11A give rise to the autosomal-recessive diseases Nijmegen breakage syndrome (NBS) and ataxia-telangiectasia-like disorder (ATLD), respectively."

Establishes the autosomal recessive, hypomorphic-allele paradigm for the MRN-complex disorders within which the index RAD50-deficient patient (compound heterozygous for two RAD50 mutations) was characterised.

PMID:41655867 SUPPORT Human Clinical

"Nijmegen breakage syndrome-like disorder (NBSLD) is a rare chromosomal instability syndrome caused by biallelic pathogenic variants in RAD50"

Directly states that NBSLD requires biallelic RAD50 variants, i.e. recessive inheritance.

◆

Subtypes

2

Classic NBSLD (growth failure and microcephaly without immunodeficiency)

The originally delineated presentation: severe pre- and postnatal growth restriction, microcephaly, "bird-like" facies, mild intellectual impairment, cellular radiosensitivity and radioresistant DNA synthesis, but without severe recurrent infection, immunoglobulin deficiency or lymphoid malignancy. The index patient remained free of malignancy to age 23 years.

Show evidence (2 references)

PMID:19409520 SUPPORT Human Clinical

"At variance with this diagnosis, she never had severe infections, had normal immunoglobulin levels, and did not develop lymphoid malignancy up to age 23 years."

Defines the distinguishing negative features of classic NBSLD relative to NBN-related Nijmegen breakage syndrome.

PMID:32212377 SUPPORT Human Clinical

"Comparison with the previously reported case and with patients presenting with NBS confirms that RAD50 mutations lead to a similar, but distinctive phenotype."

Independent confirmation that RAD50 deficiency produces a distinctive, NBS-separable phenotype.

NBSLD with bone marrow failure and B-cell immunodeficiency

An allele-dependent arm of the RAD50-deficiency spectrum in which the core growth/microcephaly phenotype is accompanied by progressive bone marrow failure and B-lymphocyte deficiency, so that NBSLD presents as an inborn error of immunity. Reported with the RAD50 E1035del separation-of-function allele and with compound heterozygosity for p.Arg83His and p.Glu485Ter.

Show evidence (2 references)

PMID:37794136 SUPPORT Human Clinical

"RAD50 deficiency/NBSLD can manifest as a distinct inborn error of immunity characterized by bone marrow failure and B-cell immunodeficiency."

Directly delineates the bone-marrow-failure/immunodeficiency arm of NBSLD.

PMID:33378670 SUPPORT Human Clinical

"Here, we identify a patient with bone marrow failure and developmental defects caused by biallelic RAD50 mutations."

Independent report of a biallelic RAD50 patient whose presentation included bone marrow failure.

◈

Mechanistic Hypotheses

1

Residual RAD50 function determines whether the immune/haematopoietic arm manifests

allele_dependent_immunohematologic_arm EMERGING

Evidence balance 3 support

Reported RAD50 genotypes segregate into a "classic" arm with growth failure and microcephaly but preserved immunity, and an arm with bone marrow failure and B-cell immunodeficiency. The proposed explanation is that different alleles preserve different MRN sub-functions: the E1035del coiled-coil allele impairs end resection and replication while sparing ATM signalling, whereas the p.Arg83His/p.Glu485Ter genotype preserves complex assembly but abolishes ATM activation. Which sub-function is retained is hypothesised to determine whether the haematopoietic/B-cell compartment decompensates. This mapping is inferred from a handful of patients and has not been tested systematically.

Show evidence (3 references)

PMID:33378670 SUPPORT In Vitro

"This mutation represents a human RAD50 separation-of-function mutation that impairs DNA repair, DNA replication, and DNA end resection without affecting ATM-dependent DNA damage response."

Demonstrates that RAD50 alleles can dissociate MRN sub-functions, the premise of the hypothesis.

PMID:41031707 SUPPORT In Vitro

"Eight missense variants, all capable of forming an MRN complex, supported the DNA damage response and mitotic features to different extents, indicating these functions are separable."

Demonstrates that RAD50 variants separate the damage-response and mitotic functions. Note the variants tested were cancer-related RAD50 missense alleles, not NBSLD patient alleles, so this supports the general principle of functional separability rather than the specific classic-versus-marrow-failure split.

PMID:41031707 SUPPORT In Vitro

"Functional heterogeneity of RAD50 variants could contribute to clinical variability."

Systematic functional dissection of cancer-related RAD50 missense variants explicitly proposes allele-level functional heterogeneity as a source of clinical variability - the premise this hypothesis extends to the NBSLD allelic spectrum, which the study itself did not test.

?

Discussions and Knowledge Gaps

3

Does RAD50 deficiency confer a cancer predisposition comparable to that of NBN-related Nijmegen breakage syndrome, or is the apparent absence of malignancy in NBSLD real?

KNOWLEDGE GAP OPEN nbsld_cancer_risk_unknown

Attached to

pathophysiology#Chromosomal instability and cellular radiosensitivity

No malignancy has been reported in the longest-followed NBSLD patients (index patient malignancy-free at 23 years; a growth-hormone-treated patient tumour-free at 5-year follow-up). But the total published cohort is fewer than ten patients with variable follow-up, and both the paralogous human diseases (NBS, ATLD) and the hypomorphic Rad50(S/S) mouse show clear cancer predisposition. Absence of evidence here is not evidence of absence, and case-report authors explicitly flag increased tumour risk when considering mitogenic therapy.

Proposed experiments

International RAD50-deficiency registry with prospective oncologic follow-up

exp_nbsld_prospective_oncologic_registry

Assemble all molecularly confirmed RAD50-deficient patients into a shared registry with standardised, prospective, lifelong cancer surveillance and a defined minimum follow-up, so that malignancy incidence can be estimated rather than inferred from scattered case reports of varying duration.

Genotype-stratified analysis of cancer incidence against residual RAD50 function

exp_nbsld_genotype_stratified_cancer_risk

Measure residual RAD50 function for each patient allele using the established lentiviral complementation assays (damage response, mitotic progression), then test whether malignancy occurrence tracks residual function - which would explain why the classic arm appears cancer-free while the mouse model is cancer-prone.

Show evidence (3 references)

PMID:41798197 SUPPORT Human Clinical

"these variants may serve as a potential molecular basis for Nijmegen Breakage Syndrome-like disease and could also increase the risk of tumor formation"

Authors of the only treated case explicitly raise unresolved tumour risk despite the absence of observed malignancy.

PMID:41798197 SUPPORT Human Clinical

"due to the rarity of cases and the short follow-up period, we cannot rule out the possibility that patients with NBSLD caused by RAD50 mutations are at an increased risk of malignancy. Patients with NBSLD caused by RAD50 mutations should be regularly monitored for tumor occurrence."

States the knowledge gap directly in the authors' own words - rarity and short follow-up prevent excluding increased malignancy risk - and gives the resulting surveillance recommendation. This is the primary warrant for this discussion.

PMID:12208847 SUPPORT Model Organism

"hypomorphic Rad50 mutant mice (Rad50(S/S) mice) exhibited growth defects and cancer predisposition"

The hypomorphic mouse model does show cancer predisposition, which is what makes the human observation surprising and the gap worth resolving.

What, if anything, should parents and other heterozygous RAD50 carriers identified through an NBSLD diagnosis be told about their own cancer risk?

INTERPRETATION OPEN rad50_heterozygous_carrier_cancer_risk

This is a carrier-level question, deliberately kept out of the disease's genetic record because it is not evidence about NBSLD itself. Monoallelic RAD50 loss-of-function is studied as a breast-cancer susceptibility allele, but the risk is not uniform across alleles: a Northern Finnish population-based study classified the recurrent founder allele RAD50 c.687delT as a moderate-risk allele, whereas broader analyses of heterozygous RAD50 pathogenic variants have not shown a consistent overall breast-cancer excess. Cascade testing after an NBSLD diagnosis will identify obligate carrier parents, so the scope and limits of that risk statement matter practically. Nothing here implies a cancer risk statement for the biallelic disease.

Show evidence (1 reference)

PMID:40009290 SUPPORT Human Clinical

"whereas CHEK2 c.1100delC, MCPH1 c.909_921del, and RAD50 c.687delT were moderate-risk alleles"

Establishes moderate breast-cancer risk specifically for the recurrent RAD50 c.687delT allele in a Northern Finnish population-based case-control study; it does not generalise to all heterozygous RAD50 variants or to any population.

Does the hypomorphic Rad50(S/S) mouse faithfully model classic human NBSLD, given that the mouse dies of bone marrow failure with cancer predisposition while classic human NBSLD patients have preserved immunity, no malignancy and a stable course?

HUMAN MODEL MISMATCH OPEN rad50_mouse_human_mismatch

Attached to

pathophysiology#Genotoxic stress in proliferating progenitor pools

The progenitor-attrition mechanism invoked for human growth failure and microcephaly is demonstrated principally in Rad50(S/S) mice, but that model's dominant outcomes - lethal haematopoietic failure and tumours - correspond to the minority bone-marrow-failure arm of the human spectrum, not the classic arm. Conversely, no mouse model reproduces the severe congenital microcephaly that defines human NBSLD. Because Rad50 nulls are embryonically lethal, viable models necessarily carry particular hypomorphic alleles whose residual activity may not correspond to any human genotype, so mechanistic inferences drawn from the mouse for the human neurodevelopmental phenotype have uncertain translational validity.

Proposed experiments

Knock-in mice carrying human NBSLD RAD50 alleles

exp_rad50_humanised_allele_knockin_mice

Generate mice bearing the specific human alleles (E1035del, p.Arg83His, the exon-15 splice allele) and compare cortical progenitor dynamics, body growth, haematopoiesis and tumour incidence, to test whether particular human alleles reproduce the classic growth/microcephaly arm rather than the murine marrow-failure/cancer phenotype.

RAD50-deficient human cerebral organoids

exp_rad50_cerebral_organoids

Derive iPSC cerebral organoids from RAD50-deficient patients and quantify neural progenitor proliferation, premature differentiation and apoptosis, mirroring the organoid work already done for NBN-related Nijmegen breakage syndrome, to test the progenitor-attrition route to microcephaly directly in human tissue.

Show evidence (2 references)

PMID:12208847 SUPPORT Model Organism

"Rad50(S/S) mice died with complete bone marrow depletion as a result of progressive hematopoietic stem cell failure."

The mouse's lethal marrow phenotype is the specific outcome that does not match classic human NBSLD.

PMID:19409520 SUPPORT Human Clinical

"she never had severe infections, had normal immunoglobulin levels, and did not develop lymphoid malignancy up to age 23 years"

The human classic phenotype lacks the haematologic and oncologic outcomes that dominate the mouse model.

⚙

Pathophysiology

8

RAD50 loss-of-function

Biallelic hypomorphic RAD50 variants (nonsense, frameshift, splice-disrupting, stop-readthrough and in-frame deletion alleles) reduce the level or stability of RAD50, the SMC-family ATPase that bridges broken DNA ends within the MRN complex. Rad50-null mice are inviable and no human with complete RAD50 loss has been reported, so viable patients are inferred to retain partial function. Note that the lethality evidence is murine; the inference to human viability has not been tested directly.

RAD50 hgnc:9816 ↓ DECREASED

RAD50 hgnc:9816

Downstream

Failure of MRN damage-focus formation and DSB sensing Loss of the RAD50 ATPase scaffold prevents productive assembly and recruitment of the MRE11-RAD50-NBN complex at double-strand breaks.

Show evidence (3 references)

PMID:19409520 SUPPORT Human Clinical

"We found that she is compound heterozygous for mutations in the RAD50 gene that give rise to low levels of unstable RAD50 protein."

Directly establishes reduced, unstable RAD50 protein as the primary molecular lesion.

PMID:32212377 SUPPORT In Vitro

"Immunoblotting experiments showed strongly reduced protein levels of RAD50 in the patient-derived fibroblasts"

Independent confirmation of reduced RAD50 protein in patient cells.

PMID:12208847 SUPPORT Model Organism

"Null mutants of each are inviable."

Supports the hypomorphic-allele requirement: complete loss of any MRN component is lethal in mouse, which is the basis for inferring that viable human patients retain partial RAD50 function. The lethality result is murine, not human.

Failure of MRN damage-focus formation and DSB sensing

The MRN complex is among the first entities recruited to a double-strand break. In RAD50-deficient patient cells, damage-induced MRN nuclear focus formation fails. The defect is in damage-recruited focus formation and sensing, NOT necessarily in complex assembly: the RAD50 E1035del coiled-coil allele still assembles an MRN complex but impairs MRE11 nuclease function and end resection, and in the p.Arg83His/p.Glu485Ter patient RAD50 expression and complex formation were maintained while ATM signalling still failed. Cryo-EM shows why assembly and signalling are separable - NBS1's ATM-recruitment motif is sequestered on the regulatory RAD50 S site and must be released for ATM activation, so RAD50 lesions can block signalling from within an intact complex.

fibroblast CL:0000057

double-strand break repair GO:0006302 ⚠ ABNORMAL

site of double-strand break GO:0035861

Downstream

Impaired ATM activation and DNA damage signaling MRN is required to recruit and activate ATM at breaks; its failure blunts the ATM-dependent phosphorylation cascade.

Impaired DNA end resection and homologous recombination repair RAD50 gates MRE11 nuclease access, so RAD50 defects impair initiation of resection and homology-directed repair.

Show evidence (4 references)

PMID:19409520 SUPPORT In Vitro

"failure to form DNA damage-induced MRN foci"

Directly documents failure of MRN focus formation in RAD50-deficient patient cells.

PMID:19409520 SUPPORT Human Clinical

"The MRE11/RAD50/NBN (MRN) complex plays a key role in recognizing and signaling DNA double-strand breaks (DSBs)."

Establishes the DSB-sensing role of the complex that RAD50 deficiency disrupts.

PMID:37794136 PARTIAL In Vitro

"The expression of RAD50 protein and MRN complex formation was maintained in the cells derived from this patient."

Qualifies the node: in some RAD50 genotypes the complex still assembles, so the downstream signalling failure is not simply a consequence of absent complex.

+ 1 more reference

Impaired ATM activation and DNA damage signaling

Radiation-induced activation of the ATM kinase and phosphorylation of its downstream substrates are markedly reduced in RAD50-deficient patient fibroblasts, phenocopying the signalling defect of ataxia-telangiectasia. Complementation with wild-type RAD50 restores ATM activation, establishing the dependency.

DNA damage checkpoint signaling GO:0000077 ↓ DECREASED DNA damage response GO:0006974 ⚠ ABNORMAL

Downstream

Cell-cycle checkpoint failure and radioresistant DNA synthesis Loss of ATM-dependent signalling disables the G1/S and intra-S checkpoints that normally suppress DNA synthesis after irradiation.

Show evidence (3 references)

PMID:19409520 SUPPORT In Vitro

"impaired radiation-induced activation of and downstream signaling through the ATM protein, which is defective in the human genetic disorder ataxia-telangiectasia"

Directly documents impaired ATM activation and downstream signalling in patient cells.

PMID:37794136 SUPPORT In Vitro

"DNA damage-induced activation of the ATM kinase was markedly decreased, which was restored by the expression of wild-type (WT) RAD50."

Complementation with wild-type RAD50 rescues ATM activation, establishing that the signalling defect is directly caused by the RAD50 lesion.

PMID:32212377 SUPPORT In Vitro

"provided evidence for a markedly reduced radiation-induced AT-mutated signaling"

Independent confirmation of reduced radiation-induced ATM signalling.

Impaired DNA end resection and homologous recombination repair

RAD50 regulates MRE11-dependent 5'-3' end resection, the committed step of homology-directed repair, and also supports replication-fork function. The RAD50 E1035del coiled-coil allele demonstrates that this arm is genetically separable from ATM signalling, defining a separation-of-function mechanism within NBSLD.

double-strand break repair via homologous recombination GO:0000724 ↓ DECREASED

Downstream

Chromosomal instability and cellular radiosensitivity Failure of homology-directed repair leaves double-strand breaks to be resolved by error-prone routes, generating breaks and rearrangements.

Show evidence (2 references)

PMID:33378670 SUPPORT In Vitro

"This mutation represents a human RAD50 separation-of-function mutation that impairs DNA repair, DNA replication, and DNA end resection without affecting ATM-dependent DNA damage response."

Establishes an ATM-independent resection/repair arm of RAD50 pathogenesis and its genetic separability from the checkpoint-signalling arm.

PMID:33378670 SUPPORT In Vitro

"Purified recombinant proteins indicate that RAD50E1035Δ impairs MRE11 nuclease activity."

Biochemical demonstration that the RAD50 lesion acts by impairing MRE11 nuclease activity.

Cell-cycle checkpoint failure and radioresistant DNA synthesis

Patient fibroblasts fail to activate the G1/S checkpoint, continue DNA synthesis after irradiation (radioresistant DNA synthesis, RDS) and accumulate in G2. RDS is the key functional diagnostic readout of NBSLD, shared with ataxia-telangiectasia, NBS and ATLD.

fibroblast CL:0000057

mitotic intra-S DNA damage checkpoint signaling GO:0031573 ↓ DECREASED

Downstream

Chromosomal instability and cellular radiosensitivity Replicating through unrepaired damage without checkpoint arrest converts lesions into chromosomal breaks and rearrangements.

Show evidence (2 references)

PMID:19409520 SUPPORT In Vitro

"These cells were also impaired in G1/S cell-cycle-checkpoint activation and displayed radioresistant DNA synthesis and G2-phase accumulation."

Directly documents checkpoint failure, RDS and G2 accumulation in patient cells.

PMID:32212377 SUPPORT In Vitro

"Using patient-derived primary fibroblasts, we could show abnormal radioresistant DNA synthesis confirming pathogenicity of the identified variant."

Independent confirmation of radioresistant DNA synthesis in a second patient.

Chromosomal instability and cellular radiosensitivity

RAD50-deficient cells display spontaneous chromosomal instability and hypersensitivity to ionizing radiation. This is the cellular hallmark shared across the chromosomal instability syndromes and underlies the clinical recommendation to minimise radiation-based imaging.

fibroblast CL:0000057

DNA repair GO:0006281 ⚠ ABNORMAL

Downstream

Genotoxic stress in proliferating progenitor pools Persistent genome instability is most consequential in tissues with high proliferative demand.

Increased sensitivity to ionizing radiation Defective double-strand break repair renders patient cells radiosensitive.

Chromosome breakage Unrepaired double-strand breaks manifest cytogenetically as chromosome breakage.

Show evidence (2 references)

PMID:19409520 SUPPORT In Vitro

"Cells from the patient were characterized by chromosomal instability; radiosensitivity"

Directly documents chromosomal instability and radiosensitivity in RAD50-deficient cells.

PMID:19409520 SUPPORT In Vitro

"The defective cellular phenotype was rescued by wild-type RAD50."

Complementation rescue establishes that the cellular instability phenotype is caused by the RAD50 lesion rather than by an unlinked variant.

Genotoxic stress in proliferating progenitor pools

Even subtle perturbation of MRN complex function generates severe genotoxic stress that is disproportionately borne by rapidly dividing progenitor compartments - neural progenitors during corticogenesis, somatic growth plates, and haematopoietic stem cells. This is the proposed convergence point linking a housekeeping DNA-repair defect to a selective growth, neurodevelopmental and marrow phenotype. The progenitor-attrition mechanism is directly demonstrated in Rad50(S/S) mice; its application to the human neurodevelopmental phenotype remains an inference.

neural progenitor cell CL:0011020 hematopoietic stem cell CL:0000037

Downstream

Microcephaly Depletion of the neural progenitor pool during corticogenesis is the inferred route to congenital microcephaly; the intermediate steps have not been demonstrated in human RAD50-deficient tissue.

Intrauterine growth retardation Reduced proliferative capacity across somatic tissues restricts prenatal growth.

Short stature Continued restriction of proliferative growth produces postnatal short stature.

Mild intellectual disability The same neural-progenitor attrition inferred to cause microcephaly is the presumed route to the accompanying mild, non-progressive cognitive impairment.

Bone marrow failure and B-lymphocyte deficiency In the marrow-failure arm, haematopoietic stem and B-lineage progenitors are the compartment that decompensates.

Show evidence (2 references)

PMID:12208847 SUPPORT Model Organism

"The data indicate that even subtle perturbation of Mre11 complex functions results in severe genotoxic stress, and that the complex is critically important for homeostasis of proliferative tissues."

Establishes in a hypomorphic Rad50 mouse that partial MRN perturbation selectively compromises proliferative tissue homeostasis via genotoxic stress.

PMID:12208847 SUPPORT Model Organism

"Rad50(S/S) mice died with complete bone marrow depletion as a result of progressive hematopoietic stem cell failure."

Demonstrates progressive haematopoietic stem cell attrition as the consequence of hypomorphic Rad50.

Bone marrow failure and B-lymphocyte deficiency

In an allele-dependent subset of patients, RAD50 deficiency decompensates the haematopoietic and B-lineage compartments, producing bone marrow failure and B-cell immunodeficiency - the feature that makes NBSLD, in these patients, an inborn error of immunity rather than a purely dysmorphic/growth syndrome.

hematopoietic stem cell CL:0000037 B cell CL:0000236

Downstream

Bone marrow hypocellularity Haematopoietic stem cell failure manifests as marrow hypocellularity.

Decreased total B cell count The B-lineage compartment is selectively depleted.

Show evidence (2 references)

PMID:37794136 SUPPORT Human Clinical

"These findings indicate important roles of RAD50 in human bone marrow and immune cells."

Establishes a RAD50-dependent requirement in human marrow and immune compartments.

PMID:33378670 SUPPORT Human Clinical

"Here, we identify a patient with bone marrow failure and developmental defects caused by biallelic RAD50 mutations."

Independent report linking biallelic RAD50 mutations to bone marrow failure.

⬡

Pathograph

Use the checkboxes to hide or show graph categories. Hover nodes for evidence and cross-linked metadata.

●

Phenotypes

28

Blood 4

Decreased total lymphocyte count Decreased total lymphocyte count HP:0001888

Show evidence (1 reference)

PMID:41655867 SUPPORT Human Clinical

"The immunological assessment revealed borderline lymphopenia without overt immunodeficiency."

Documents borderline lymphopenia while explicitly excluding overt immunodeficiency in the same patient.

Thrombocytopenia Thrombocytopenia HP:0001873

Show evidence (1 reference)

PMID:33378670 SUPPORT Human Clinical

"P1's cell blood count revealed thrombocytopenia (platelet count of 113 G/L) associated with anemia (hemoglobin level of 10 g/dL) and neutropenia (neutrophil count of 1 G/L)"

Quantified thrombocytopenia in the marrow-failure patient.

Anemia Anemia HP:0001903

Show evidence (1 reference)

PMID:33378670 SUPPORT Human Clinical

"P1's cell blood count revealed thrombocytopenia (platelet count of 113 G/L) associated with anemia (hemoglobin level of 10 g/dL) and neutropenia (neutrophil count of 1 G/L)"

Quantified anemia in the marrow-failure patient.

Decreased total neutrophil count Decreased total neutrophil count HP:0001875

Show evidence (1 reference)

PMID:33378670 SUPPORT Human Clinical

"P1's cell blood count revealed thrombocytopenia (platelet count of 113 G/L) associated with anemia (hemoglobin level of 10 g/dL) and neutropenia (neutrophil count of 1 G/L)"

Quantified neutropenia in the marrow-failure patient.

Eye 1

Cataract Cataract HP:0000518

Show evidence (1 reference)

PMID:33378670 SUPPORT Human Clinical

"P1 also developed a cataract at 10 years of age that necessitated surgical intervention."

Directly documents early-onset cataract requiring surgery in a RAD50-deficient patient.

Genitourinary 1

Cryptorchidism Cryptorchidism HP:0000028

Show evidence (1 reference)

PMID:41655867 SUPPORT Human Clinical

"We report a 6-year-old Chinese boy, who presented with bilateral cryptorchidism, severe microcephaly, growth retardation"

Directly documents bilateral cryptorchidism in a reported NBSLD patient.

Head and Neck 2

Microcephaly VERY_FREQUENT Microcephaly HP:0000252

Show evidence (3 references)

PMID:19409520 SUPPORT Human Clinical

"Here, we report on a patient previously diagnosed as probably having NBS, with microcephaly, mental retardation, 'bird-like' face, and short stature."

Directly documents microcephaly in the index RAD50-deficient patient.

PMID:41798197 SUPPORT Human Clinical

"Human RAD50 gene mutations cause Nijmegen Breakage Syndrome-like disease, characterized by severe prenatal and postpartum growth retardation and microcephaly."

Characterises microcephaly as a defining feature of the disorder, supporting the VERY_FREQUENT band.

PMID:41655867 SUPPORT Human Clinical

"who presented with bilateral cryptorchidism, severe microcephaly, growth retardation, multiple café-au-lait macules, brachydactyly, and distinctive craniofacial features"

Confirms severe microcephaly in an additional independently reported patient.

Micrognathia Micrognathia HP:0000347

Show evidence (1 reference)

PMID:41798197 SUPPORT Human Clinical

"he had obvious facial deformities, including receding forehead, long and narrow nasal bridge, small and prominent mouth, smooth and short philtrum, and micrognathia"

Directly documents micrognathia within the craniofacial phenotype.

Immune 1

Immunodeficiency Immunodeficiency HP:0002721

Do not read this record as a disease-level assertion. In classic NBSLD immunodeficiency is absent: the index patient "never had severe infections, had normal immunoglobulin levels, and did not develop lymphoid malignancy up to age 23 years" (PMID:19409520), which is precisely what separates NBSLD from NBN-related Nijmegen breakage syndrome. That contrast is recorded on the Classic NBSLD subtype and on the Nijmegen breakage syndrome differential diagnosis.

Show evidence (1 reference)

PMID:37794136 SUPPORT Human Clinical

"RAD50 deficiency/NBSLD can manifest as a distinct inborn error of immunity characterized by bone marrow failure and B-cell immunodeficiency."

Supports immunodeficiency specifically in the marrow-failure arm, establishing that the feature is allele-dependent rather than a disease-wide manifestation.

Integument 3

Cafe-au-lait spot Cafe-au-lait spot HP:0000957

Show evidence (1 reference)

PMID:41655867 SUPPORT Human Clinical

"severe microcephaly, growth retardation, multiple café-au-lait macules, brachydactyly"

Directly documents multiple cafe-au-lait macules in a reported NBSLD patient.

Abnormality of skin pigmentation Abnormality of skin pigmentation HP:0001000

Show evidence (1 reference)

PMID:33378670 SUPPORT Human Clinical

"physical examination of P1 revealed failure to thrive (height of 108.5 cm, <3rd percentile; weight of 17.2 kg, <3rd percentile), skin pigmentation, nail dysplasia, leukoplakia, dental loss, microcephaly"

Documents abnormal skin pigmentation as part of the mucocutaneous triad.

Nail dysplasia Nail dysplasia HP:0002164

Show evidence (1 reference)

PMID:33378670 SUPPORT Human Clinical

"skin pigmentation, nail dysplasia, leukoplakia, dental loss, microcephaly"

Documents nail dysplasia in the marrow-failure patient.

Limbs 1

Brachydactyly Brachydactyly HP:0001156

Show evidence (1 reference)

PMID:41655867 SUPPORT Human Clinical

"multiple café-au-lait macules, brachydactyly, and distinctive craniofacial features"

Directly documents brachydactyly in a reported NBSLD patient.

Nervous System 1

Mild intellectual disability VERY_FREQUENT Mild intellectual disability HP:0001256

Show evidence (3 references)

PMID:41655867 SUPPORT Human Clinical

"Mild intellectual impairment was confirmed on formal neurocognitive testing."

Formal neurocognitive testing documenting mild intellectual impairment.

PMID:19409520 PARTIAL Human Clinical

"with microcephaly, mental retardation, 'bird-like' face, and short stature"

Documents intellectual disability in the index patient; the abstract does not grade severity, so this supports the phenotype but not specifically the "mild" qualifier.

PMID:41798197 SUPPORT Human Clinical

"They all exhibit normal sexual development and show no decline in nervous system; they only demonstrate mild learning disabilities."

Frequency basis for VERY_FREQUENT, and the warrant for the MILD qualifier: a cross-patient synthesis stating that the reported RAD50 patients "all" show no neurological decline and demonstrate "only" mild learning disabilities. This resolves the earlier gap where no source graded severity across patients. Snippet retains the source PDF line breaks so it matches the cached body exactly.

Cellular 1

Increased sensitivity to ionizing radiation Increased sensitivity to ionizing radiation HP:0011133

Show evidence (2 references)

PMID:19409520 SUPPORT In Vitro

"Cells from the patient were characterized by chromosomal instability; radiosensitivity"

Directly documents cellular radiosensitivity in the index patient.

PMID:37794136 PARTIAL In Vitro

"Radiosensitivity appeared inconspicuous in the patient-derived cell line as assessed by colony formation assay."

Qualifies the phenotype: radiosensitivity is genotype-dependent and was not detectable by colony formation assay in this patient, so a normal assay does not exclude NBSLD.

Growth 4

Intrauterine growth retardation Intrauterine growth retardation HP:0001511

Show evidence (1 reference)

PMID:41798197 SUPPORT Human Clinical

"characterized by severe prenatal and postpartum growth retardation and microcephaly"

Directly documents prenatal (intrauterine) growth retardation as a defining feature.

Postnatal growth retardation Postnatal growth retardation HP:0008897

Show evidence (1 reference)

PMID:41798197 SUPPORT Human Clinical

"The boy was born at full term, with substantial growth retardation from infancy to early childhood."

Documents postnatal growth retardation from infancy in a reported NBSLD patient.

Short stature VERY_FREQUENT Short stature HP:0004322

Show evidence (4 references)

PMID:19409520 SUPPORT Human Clinical

"with microcephaly, mental retardation, 'bird-like' face, and short stature"

Documents short stature in the index patient.

PMID:32212377 SUPPORT Human Clinical

"we report a long-term follow-up of an unrelated patient with facial dysmorphisms, microcephaly, skeletal features, and short stature"

Confirms short stature in the second reported patient.

PMID:37794136 SUPPORT Human Clinical

"We report on a girl with microcephaly, mental retardation, bird-like face, short stature, bone marrow failure and B-cell immunodeficiency."

Confirms short stature in a third independently reported patient.

+ 1 more reference

Failure to thrive Failure to thrive HP:0001508

Show evidence (1 reference)

PMID:33378670 SUPPORT Human Clinical

"physical examination of P1 revealed failure to thrive (height of 108.5 cm, <3rd percentile; weight of 17.2 kg, <3rd percentile)"

Documents quantified failure to thrive in a RAD50-deficient patient.

Other 9

Bird-like facies Bird-like facies HP:0000320

Show evidence (2 references)

PMID:19409520 SUPPORT Human Clinical

"with microcephaly, mental retardation, 'bird-like' face, and short stature"

Directly documents bird-like facies in the index patient.

PMID:37794136 SUPPORT Human Clinical

"We report on a girl with microcephaly, mental retardation, bird-like face, short stature, bone marrow failure and B-cell immunodeficiency."

Confirms bird-like facies in an independently reported patient.

Sloping forehead Sloping forehead HP:0000340

Show evidence (1 reference)

PMID:41655867 SUPPORT Human Clinical

"including a sloping forehead, midface prominence, and receding mandible"

Directly documents a sloping forehead as part of the craniofacial phenotype.

Chromosome breakage Chromosome breakage HP:0040012

Show evidence (2 references)

PMID:19409520 SUPPORT In Vitro

"Cells from the patient were characterized by chromosomal instability; radiosensitivity"

Directly documents chromosomal instability in RAD50-deficient patient cells.

PMID:41655867 SUPPORT Human Clinical

"Nijmegen breakage syndrome-like disorder (NBSLD) is a rare chromosomal instability syndrome caused by biallelic pathogenic variants in RAD50"

Classifies NBSLD as a chromosomal instability syndrome.

Bone marrow hypocellularity Bone marrow hypocellularity HP:0005528

Show evidence (2 references)

PMID:37794136 SUPPORT Human Clinical

"RAD50 deficiency/NBSLD can manifest as a distinct inborn error of immunity characterized by bone marrow failure and B-cell immunodeficiency."

Directly documents bone marrow failure as part of the NBSLD spectrum.

PMID:33378670 SUPPORT Human Clinical

"Here, we identify a patient with bone marrow failure and developmental defects caused by biallelic RAD50 mutations."

Independent report of bone marrow failure in a biallelic RAD50 patient.

Decreased total B cell count Decreased total B cell count HP:0010976

Show evidence (1 reference)

PMID:37794136 SUPPORT Human Clinical

"We report on a girl with microcephaly, mental retardation, bird-like face, short stature, bone marrow failure and B-cell immunodeficiency."

Directly documents B-cell immunodeficiency in a RAD50-deficient patient.

Aplastic anemia Aplastic anemia HP:0001915

Show evidence (1 reference)

PMID:33378670 SUPPORT Human Clinical

"Bone marrow smears and biopsies showed reduced cellularity (15%) without myelodysplastic features, consistent with aplastic anemia."

Documents quantified marrow hypocellularity read as aplastic anemia, explicitly excluding myelodysplasia.

Oral leukoplakia Oral leukoplakia HP:0002745

Show evidence (1 reference)

PMID:33378670 SUPPORT Human Clinical

"skin pigmentation, nail dysplasia, leukoplakia, dental loss, microcephaly"

Documents leukoplakia in the marrow-failure patient.

Premature loss of teeth Premature loss of teeth HP:0006480

Show evidence (1 reference)

PMID:33378670 SUPPORT Human Clinical

"skin pigmentation, nail dysplasia, leukoplakia, dental loss, microcephaly"

Documents dental loss in the marrow-failure patient.

Retrognathia Retrognathia HP:0000278

Show evidence (1 reference)

PMID:41655867 SUPPORT Human Clinical

"including a sloping forehead, midface prominence, and receding mandible"

Directly documents a receding mandible as part of the craniofacial phenotype.

🧬

Genetic Associations

1

RAD50 (Causal biallelic hypomorphic/loss-of-function variants; complete RAD50 loss is not compatible with viability, so patients are compound heterozygous or homozygous for partial-function alleles.)

Gene: RAD50 hgnc:9816 relationship_type: CAUSATIVE variant_origin: GERMLINE

Show evidence (3 references)

PMID:19409520 SUPPORT Human Clinical

"In conclusion, we have identified and characterized a patient with a RAD50 deficiency that results in a clinical phenotype that can be classified as an NBS-like disorder (NBSLD)."

Establishes RAD50 as the causal gene for NBSLD.

PMID:41655867 SUPPORT Human Clinical

"caused by biallelic pathogenic variants in RAD50, which is a key component of the MRE11-RAD50-NBS1 (MRN) complex involved in DNA double-strand break repair"

Confirms biallelic RAD50 variants as the molecular cause and situates RAD50 in the MRN complex.

PMID:19409520 SUPPORT Human Clinical

"To date, no disease due to RAD50 deficiency has been described."

Records that this report established the gene-disease relationship for RAD50, which had no prior disease association.

💊

Medical Actions

4

Recombinant human growth hormone

Action: Pharmacotherapy NCIT:C15986

Agent: somatropin NCIT:C837

Somatropin has been used off-label for the short stature of NBSLD. In the single reported experience, 5 years 9 months of therapy improved height from -3.35 SD to -1.28 SD with no tumour at 5-year post-discontinuation follow-up. IMPORTANT SAFETY CAVEAT - in that case growth hormone was started by junior physicians before any genetic evaluation; the authors emphasise that genetic evaluation should precede growth-promoting therapy in syndromic short stature, because growth hormone/IGF-1 signalling is mitogenic and the underlying DNA repair deficiency may raise tumour risk. The evidence base is one patient.

Target Phenotypes: Short stature HP:0004322

Show evidence (2 references)

PMID:41798197 SUPPORT Human Clinical

"Although recombinant human growth hormone significantly improved the patient's growth rate (from -3.35 SD to -1.28 SD), these variants may serve as a potential molecular basis for Nijmegen Breakage Syndrome-like disease and could also increase the risk of tumor formation."

Reports both the growth benefit and the explicit tumour-risk caution attached to it in the single documented NBSLD growth hormone experience.

PMID:41798197 SUPPORT Human Clinical

"At the age of 4.5 years, the child with syndromic short stature was prescribed recombinant human growth hormone for height correction by junior resident physicians, with no genetic evaluation performed prior to treatment."

Documents the safety lesson that the therapy was given without prior genetic evaluation, which the report frames as the central cautionary finding.

Surveillance-based supportive management

Action: supportive care Ontology label: Supportive Care NCIT:C15747

In the absence of any disease-modifying therapy, reported NBSLD patients are managed with regular clinical surveillance and multidisciplinary supportive care. Because patient cells are radiosensitive, non-ionizing imaging (MRI, ultrasound) is preferred over CT and plain radiography where feasible.

Show evidence (2 references)

PMID:41655867 SUPPORT Human Clinical

"However, it is not presently required for this patient, who is managed with regular surveillance."

Documents surveillance-based management as the current standard for an NBSLD patient.

PMID:41798197 SUPPORT Human Clinical

"Due to the DNA damage repair defect, repeated X-ray or CT scans should be avoided, and MRI or ultrasound scans should be used instead."

Directly supports the imaging-modality recommendation, which was previously asserted in the description without a supporting citation.

Allogeneic hematopoietic stem cell transplantation

Action: hematopoietic stem cell transplantation Ontology label: Hematopoietic Cell Transplantation NCIT:C15431

HSCT has been proposed as a potential therapeutic option for DNA damage repair disorders and would be the standard consideration for the bone-marrow-failure arm of NBSLD. It has been raised but not required in the reported cases, so this is a proposed rather than established indication for this specific disorder.

Mechanism Target:

INHIBITS Bone marrow failure and B-lymphocyte deficiency — Replacing the RAD50-deficient haematopoietic stem cell compartment with donor cells removes the failing compartment itself. It does not correct the RAD50 defect in neural, skeletal or other somatic tissue, so it addresses only the haematologic arm.

Target Phenotypes: Bone marrow hypocellularity HP:0005528

Show evidence (1 reference)

PMID:41655867 PARTIAL Human Clinical

"Allogeneic hematopoietic stem cell transplantation (HSCT) has been proposed as a potential therapeutic option for DNA damage repair disorders."

Supports HSCT as a proposed option for DNA damage repair disorders; the same report makes clear it was not required in this patient, so the evidence is partial.

Genetic counseling

Action: genetic counseling Ontology label: Genetic Counseling NCIT:C15240

Autosomal recessive inheritance carries a 25% recurrence risk per pregnancy for carrier couples. Counseling should also cover the recommendation that molecular diagnosis precede any elective growth-promoting therapy.

🔀

Differential Diagnoses

4

Conditions with similar clinical presentations that must be differentiated from Nijmegen Breakage Syndrome-like Disorder:

Nijmegen breakage syndrome MONDO:0009623

Overlapping Features The NBN-related disorder that NBSLD phenocopies. Shares microcephaly, growth failure, bird-like facies, chromosomal instability and radiosensitivity.

Distinguishing Features

Combined cellular and humoral immunodeficiency with recurrent sinopulmonary infection is characteristic of NBS but absent in classic NBSLD.
Strong predisposition to lymphoid malignancy is characteristic of NBS; the longest-followed NBSLD patient was malignancy-free at 23 years.
Premature ovarian failure in females is characteristic of NBS and has not been reported in NBSLD.
Intellectual abilities decline over time in NBS, whereas NBSLD cognition has been stable and non-progressive.
Early growth deficiency improves with age in NBS, whereas NBSLD growth restriction persists into adulthood.
Causal gene is NBN in NBS versus RAD50 in NBSLD.

Show evidence (3 references)

PMID:19409520 SUPPORT Human Clinical

"Here, we report on a patient previously diagnosed as probably having NBS, with microcephaly, mental retardation, 'bird-like' face, and short stature. At variance with this diagnosis, she never had severe infections, had normal immunoglobulin levels, and did not develop lymphoid malignancy up to..."

Documents both the initial misdiagnosis as NBS and the specific features that distinguish NBSLD from it.

PMID:20301355 SUPPORT Human Clinical

"Nijmegen breakage syndrome (NBS) is characterized by progressive microcephaly, early growth deficiency that improves with age, recurrent respiratory infections, an increased risk for malignancy (primarily lymphoma), and premature ovarian failure in females."

The GeneReviews chapter for NBS - the differential, not for NBSLD - supplies the authoritative NBS feature set. Recurrent respiratory infection, lymphoma risk and premature ovarian failure are absent from classic NBSLD, and NBS growth deficiency improves with age whereas NBSLD growth restriction persists.

PMID:20301355 SUPPORT Human Clinical

"Intellectual abilities tend to decline over time."

Cognitive decline over time is characteristic of NBS, whereas NBSLD cognition has been described as stable and non-progressive - a further discriminator between the two.

Ataxia-telangiectasia-like disorder Not Yet Curated MONDO:0024557

Overlapping Features The MRE11-related member of the MRN-complex disease triad. Shares radiosensitivity and defective ATM signalling with NBSLD.

Distinguishing Features

ATLD is dominated by progressive cerebellar ataxia and neurodegeneration, whereas NBSLD cognition has been non-progressive in the best-followed patients.
Severe congenital microcephaly with pre- and postnatal growth failure is the leading feature of NBSLD rather than of ATLD.
Causal gene is MRE11A in ATLD versus RAD50 in NBSLD.

Show evidence (2 references)

PMID:19409520 SUPPORT Human Clinical

"Hypomorphic mutations in NBN (previously known as NBS1) and MRE11A give rise to the autosomal-recessive diseases Nijmegen breakage syndrome (NBS) and ataxia-telangiectasia-like disorder (ATLD), respectively."

Establishes ATLD as the MRE11A-related sibling disorder within the MRN triad.

PMID:38686720 SUPPORT Other

"we discuss the human diseases such as ataxia-telangiectasia-like disorder,Nijmegen breakage syndrome,and Nijmegen breakage syndrome-like disorder that are caused by dysfunctions in the MRN complex"

A dedicated MRN review that treats ATLD, NBS and NBSLD as the three MRN-complex disorders, supporting the triad framing on which this differential rests.

Ataxia-telangiectasia MONDO:0008840

Overlapping Features The ATM-related disorder whose cellular phenotype NBSLD closely mimics - impaired ATM signalling, radioresistant DNA synthesis and radiosensitivity are shared.

Distinguishing Features

Progressive cerebellar ataxia and oculocutaneous telangiectasia characterise A-T and are not features of NBSLD.
The primary lesion is in ATM itself in A-T, versus upstream MRN/RAD50 in NBSLD.

Show evidence (1 reference)

PMID:19409520 SUPPORT In Vitro

"impaired radiation-induced activation of and downstream signaling through the ATM protein, which is defective in the human genetic disorder ataxia-telangiectasia"

Documents the shared ATM-signalling defect that makes A-T the key cellular-phenotype differential.

Dyskeratosis congenita MONDO:0015780

Overlapping Features Relevant specifically to the bone-marrow-failure arm. The E1035del patient presented with marrow failure plus the classic dyskeratosis congenita mucocutaneous triad - skin pigmentation, nail dysplasia and leukoplakia - which the authors read as suggesting a DNA repair and/or telomere maintenance defect. A telomere-biology disorder is therefore the leading alternative diagnosis in an NBSLD patient presenting this way.

Distinguishing Features

Severe congenital microcephaly with pre- and postnatal growth restriction is characteristic of NBSLD and not of dyskeratosis congenita.
Dyskeratosis congenita is caused by telomere-maintenance gene defects with short telomeres, whereas NBSLD is caused by biallelic RAD50 variants affecting DSB sensing.
Radioresistant DNA synthesis and impaired ATM activation point to NBSLD rather than a telomere-biology disorder.

Show evidence (1 reference)

PMID:33378670 SUPPORT Human Clinical

"Collectively, P1's clinical features were reminiscent of a defect in DNA repair and/or telomere maintenance"

The authors explicitly flag telomere maintenance as the competing explanation for this presentation, which is what makes dyskeratosis congenita the relevant differential for the marrow-failure arm.

{ }

Source YAML

click to show

name: Nijmegen Breakage Syndrome-like Disorder
creation_date: "2026-07-31T00:00:00Z"
description: >-
  Nijmegen breakage syndrome-like disorder (NBSLD, RAD50 deficiency) is an
  ultra-rare autosomal recessive chromosomal instability syndrome caused by
  biallelic hypomorphic variants in RAD50, the SMC-family ATPase core of the
  MRE11-RAD50-NBN (MRN) DNA double-strand break sensor complex. RAD50 loss
  destabilises the MRN complex, abolishes damage-induced MRN focus formation and
  impairs ATM activation, producing cell-cycle checkpoint failure, radioresistant
  DNA synthesis, radiosensitivity and chromosomal instability. Clinically it
  phenocopies Nijmegen breakage syndrome - severe pre- and postnatal growth
  restriction, microcephaly, "bird-like" facies and mild intellectual impairment -
  but the originally described patients lacked severe infections, immunoglobulin
  deficiency and lymphoid malignancy, which is the feature that distinguishes NBSLD
  from NBN-related NBS. A subsequently recognised, allele-dependent arm of the
  spectrum does manifest bone marrow failure with B-cell immunodeficiency.
category: Mendelian
parents:
- hereditary disease
- chromosomal instability syndrome
- DNA repair disease
synonyms:
- NBSLD
- RAD50 deficiency
- NBS-like disorder
- microcephaly and chromosomal instability without immunodeficiency
disease_term:
  preferred_term: Nijmegen breakage syndrome-like disorder
  term:
    id: MONDO:0013118
    label: Nijmegen breakage syndrome-like disorder
classifications:
  harrisons_chapter:
  - classification_value: GENETICS_ENVIRONMENT_DISEASE
  - classification_value: ONCOLOGY_HEMATOLOGY
  iuis_category:
    classification_value: bone marrow failure
    notes: >-
      Applies only to the NBSLD-with-bone-marrow-failure arm, where the disorder presents
      as an inborn error of immunity. Classic NBSLD has no immunodeficiency and would not
      be classified in the IUIS scheme at all.
    evidence:
    - reference: PMID:37794136
      reference_title: Bone Marrow Failure and Immunodeficiency Associated with Human RAD50 Variants.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "RAD50 deficiency/NBSLD can manifest as a distinct inborn error of immunity characterized by bone marrow failure and B-cell immunodeficiency."
      explanation: >-
        Explicitly classifies the marrow-failure arm of RAD50 deficiency as an inborn error
        of immunity characterised by bone marrow failure.
inheritance:
- name: Autosomal recessive inheritance
  description: >-
    NBSLD is caused by biallelic (compound heterozygous or homozygous)
    hypomorphic RAD50 variants and segregates as an autosomal recessive trait,
    in parallel with the other two MRN-complex disorders (NBN-related Nijmegen
    breakage syndrome and MRE11-related ataxia-telangiectasia-like disorder).
  inheritance_term:
    preferred_term: Autosomal recessive inheritance
    term:
      id: HP:0000007
      label: Autosomal recessive inheritance
  evidence:
  - reference: PMID:19409520
    reference_title: Human RAD50 deficiency in a Nijmegen breakage syndrome-like disorder.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Hypomorphic mutations in NBN (previously known as NBS1) and MRE11A give rise to the autosomal-recessive diseases Nijmegen breakage syndrome (NBS) and ataxia-telangiectasia-like disorder (ATLD), respectively."
    explanation: >-
      Establishes the autosomal recessive, hypomorphic-allele paradigm for the MRN-complex
      disorders within which the index RAD50-deficient patient (compound heterozygous for
      two RAD50 mutations) was characterised.
  - reference: PMID:41655867
    reference_title: "Expanding the mutational spectrum of RAD50: a case report of Nijmegen breakage syndrome-like disorder in a Chinese child."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Nijmegen breakage syndrome-like disorder (NBSLD) is a rare chromosomal instability syndrome caused by biallelic pathogenic variants in RAD50"
    explanation: Directly states that NBSLD requires biallelic RAD50 variants, i.e. recessive inheritance.
has_subtypes:
- name: Classic NBSLD
  display_name: Classic NBSLD (growth failure and microcephaly without immunodeficiency)
  description: >-
    The originally delineated presentation: severe pre- and postnatal growth
    restriction, microcephaly, "bird-like" facies, mild intellectual impairment,
    cellular radiosensitivity and radioresistant DNA synthesis, but without severe
    recurrent infection, immunoglobulin deficiency or lymphoid malignancy. The index
    patient remained free of malignancy to age 23 years.
  evidence:
  - reference: PMID:19409520
    reference_title: Human RAD50 deficiency in a Nijmegen breakage syndrome-like disorder.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "At variance with this diagnosis, she never had severe infections, had normal immunoglobulin levels, and did not develop lymphoid malignancy up to age 23 years."
    explanation: >-
      Defines the distinguishing negative features of classic NBSLD relative to NBN-related
      Nijmegen breakage syndrome.
  - reference: PMID:32212377
    reference_title: "Human RAD50 deficiency: Confirmation of a distinctive phenotype."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Comparison with the previously reported case and with patients presenting with NBS confirms that RAD50 mutations lead to a similar, but distinctive phenotype."
    explanation: Independent confirmation that RAD50 deficiency produces a distinctive, NBS-separable phenotype.
- name: NBSLD with bone marrow failure
  display_name: NBSLD with bone marrow failure and B-cell immunodeficiency
  description: >-
    An allele-dependent arm of the RAD50-deficiency spectrum in which the core
    growth/microcephaly phenotype is accompanied by progressive bone marrow failure
    and B-lymphocyte deficiency, so that NBSLD presents as an inborn error of
    immunity. Reported with the RAD50 E1035del separation-of-function allele and with
    compound heterozygosity for p.Arg83His and p.Glu485Ter.
  evidence:
  - reference: PMID:37794136
    reference_title: Bone Marrow Failure and Immunodeficiency Associated with Human RAD50 Variants.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "RAD50 deficiency/NBSLD can manifest as a distinct inborn error of immunity characterized by bone marrow failure and B-cell immunodeficiency."
    explanation: Directly delineates the bone-marrow-failure/immunodeficiency arm of NBSLD.
  - reference: PMID:33378670
    reference_title: A Disease-Causing Single Amino Acid Deletion in the Coiled-Coil Domain of RAD50 Impairs MRE11 Complex Functions in Yeast and Humans.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Here, we identify a patient with bone marrow failure and developmental defects caused by biallelic RAD50 mutations."
    explanation: Independent report of a biallelic RAD50 patient whose presentation included bone marrow failure.
prevalence:
- population: Worldwide
  measure_type: CASES_IN_LITERATURE
  prevalence_class: BELOW_1_IN_1000000
  notes: >-
    Ascertainment is limited to individual case reports. The two 2026 reports quoted below
    describe the literature as "less than 5 cases" and "merely few cases" respectively;
    counting the distinct patient genotypes curated in this entry's variants section plus
    the separately reported E1035del patient gives on the order of six molecularly
    confirmed patients, so the two 2026 phrasings are best read as approximate rather than
    exact. No population-based prevalence estimate exists.
  evidence:
  - reference: PMID:41798197
    reference_title: Novel RAD50 variants lead to Nijmegen Breakage Syndrome-like disorder and unplanned recombinant human growth hormone treatment response.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "It is very rare (less than 5 cases) with limited clinical data and treatment experience."
    explanation: Directly supports an ultra-rare, case-report-only occurrence for NBSLD.
  - reference: PMID:41655867
    reference_title: "Expanding the mutational spectrum of RAD50: a case report of Nijmegen breakage syndrome-like disorder in a Chinese child."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Merely few cases have been reported worldwide, and its phenotypic spectrum remains incompletely defined."
    explanation: Confirms that worldwide ascertainment is limited to a handful of reported cases.
progression:
- phase: Congenital onset with prenatal growth restriction and microcephaly
  age_range: Prenatal to infancy
  notes: >-
    Growth restriction begins in utero and continues after birth, with microcephaly
    apparent congenitally.
  evidence:
  - reference: PMID:41798197
    reference_title: Novel RAD50 variants lead to Nijmegen Breakage Syndrome-like disorder and unplanned recombinant human growth hormone treatment response.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Human RAD50 gene mutations cause Nijmegen Breakage Syndrome-like disease, characterized by severe prenatal and postpartum growth retardation and microcephaly."
    explanation: Establishes prenatal onset of the growth phenotype with postnatal continuation.
- phase: Childhood - stable dysmorphic and growth phenotype, long-term follow-up without malignancy
  subtype: Classic NBSLD
  age_range: Childhood to early adulthood
  notes: >-
    In the classic arm, long-term follow-up has documented persistence of the growth
    and craniofacial phenotype without emergence of severe infection or lymphoid
    malignancy; the index patient was malignancy-free at age 23 years.
  evidence:
  - reference: PMID:19409520
    reference_title: Human RAD50 deficiency in a Nijmegen breakage syndrome-like disorder.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "she never had severe infections, had normal immunoglobulin levels, and did not develop lymphoid malignancy up to age 23 years"
    explanation: Documents the long-term course of the classic NBSLD arm through early adulthood.
  - reference: PMID:32212377
    reference_title: "Human RAD50 deficiency: Confirmation of a distinctive phenotype."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Here, we report a long-term follow-up of an unrelated patient with facial dysmorphisms, microcephaly, skeletal features, and short stature who is homozygous for a novel variant in RAD50."
    explanation: Provides a second long-term follow-up of the stable classic phenotype.
- phase: Childhood-onset progressive marrow failure
  subtype: NBSLD with bone marrow failure
  age_range: Childhood
  notes: >-
    In the marrow-failure arm the haematological phenotype is superimposed on the
    congenital growth/microcephaly phenotype and is progressive rather than static.
  evidence:
  - reference: PMID:37794136
    reference_title: Bone Marrow Failure and Immunodeficiency Associated with Human RAD50 Variants.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We report on a girl with microcephaly, mental retardation, bird-like face, short stature, bone marrow failure and B-cell immunodeficiency."
    explanation: Documents marrow failure arising on the background of the congenital NBSLD phenotype.
pathophysiology:
- name: RAD50 loss-of-function
  biological_scale: MOLECULAR
  description: >-
    Biallelic hypomorphic RAD50 variants (nonsense, frameshift, splice-disrupting,
    stop-readthrough and in-frame deletion alleles) reduce the level or stability of
    RAD50, the SMC-family ATPase that bridges broken DNA ends within the MRN complex.
    Rad50-null mice are inviable and no human with complete RAD50 loss has been reported,
    so viable patients are inferred to retain partial function. Note that the lethality
    evidence is murine; the inference to human viability has not been tested directly.
  gene:
    preferred_term: RAD50
    description: RAD50 double-strand break repair protein, the ATPase core of the MRN complex.
    modifier: DECREASED
    term:
      id: hgnc:9816
      label: RAD50
  genes:
  - preferred_term: RAD50
    term:
      id: hgnc:9816
      label: RAD50
  evidence:
  - reference: PMID:19409520
    reference_title: Human RAD50 deficiency in a Nijmegen breakage syndrome-like disorder.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We found that she is compound heterozygous for mutations in the RAD50 gene that give rise to low levels of unstable RAD50 protein."
    explanation: Directly establishes reduced, unstable RAD50 protein as the primary molecular lesion.
  - reference: PMID:32212377
    reference_title: "Human RAD50 deficiency: Confirmation of a distinctive phenotype."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Immunoblotting experiments showed strongly reduced protein levels of RAD50 in the patient-derived fibroblasts"
    explanation: Independent confirmation of reduced RAD50 protein in patient cells.
  - reference: PMID:12208847
    reference_title: Cancer predisposition and hematopoietic failure in Rad50(S/S) mice.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Null mutants of each are inviable."
    explanation: >-
      Supports the hypomorphic-allele requirement: complete loss of any MRN component is
      lethal in mouse, which is the basis for inferring that viable human patients retain
      partial RAD50 function. The lethality result is murine, not human.
  downstream:
  - target: Failure of MRN damage-focus formation and DSB sensing
    causal_link_type: DIRECT
    description: >-
      Loss of the RAD50 ATPase scaffold prevents productive assembly and recruitment of
      the MRE11-RAD50-NBN complex at double-strand breaks.
- name: Failure of MRN damage-focus formation and DSB sensing
  biological_scale: MOLECULAR
  description: >-
    The MRN complex is among the first entities recruited to a double-strand break.
    In RAD50-deficient patient cells, damage-induced MRN nuclear focus formation fails.
    The defect is in damage-recruited focus formation and sensing, NOT necessarily in
    complex assembly: the RAD50 E1035del coiled-coil allele still assembles an MRN
    complex but impairs MRE11 nuclease function and end resection, and in the
    p.Arg83His/p.Glu485Ter patient RAD50 expression and complex formation were maintained
    while ATM signalling still failed. Cryo-EM shows why assembly and signalling are
    separable - NBS1's ATM-recruitment motif is sequestered on the regulatory RAD50 S
    site and must be released for ATM activation, so RAD50 lesions can block signalling
    from within an intact complex.
  cell_types:
  - preferred_term: fibroblast
    term:
      id: CL:0000057
      label: fibroblast
  biological_processes:
  - preferred_term: double-strand break repair
    modifier: ABNORMAL
    term:
      id: GO:0006302
      label: double-strand break repair
  cellular_components:
  - preferred_term: site of double-strand break
    term:
      id: GO:0035861
      label: site of double-strand break
  evidence:
  - reference: PMID:19409520
    reference_title: Human RAD50 deficiency in a Nijmegen breakage syndrome-like disorder.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "failure to form DNA damage-induced MRN foci"
    explanation: Directly documents failure of MRN focus formation in RAD50-deficient patient cells.
  - reference: PMID:19409520
    reference_title: Human RAD50 deficiency in a Nijmegen breakage syndrome-like disorder.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The MRE11/RAD50/NBN (MRN) complex plays a key role in recognizing and signaling DNA double-strand breaks (DSBs)."
    explanation: Establishes the DSB-sensing role of the complex that RAD50 deficiency disrupts.
  - reference: PMID:37794136
    reference_title: Bone Marrow Failure and Immunodeficiency Associated with Human RAD50 Variants.
    supports: PARTIAL
    evidence_source: IN_VITRO
    snippet: "The expression of RAD50 protein and MRN complex formation was maintained in the cells derived from this patient."
    explanation: >-
      Qualifies the node: in some RAD50 genotypes the complex still assembles, so the
      downstream signalling failure is not simply a consequence of absent complex.
  - reference: PMID:40968163
    reference_title: Structural basis for DNA break sensing by human MRE11-RAD50-NBS1 and its regulation by telomeric factor TRF2.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "MRN senses DSBs through a tight clamp-like sensing state with closed coiled-coil domains, but auto-inhibited MRE11 nuclease. NBS1 wraps around the MRE11 dimer, with NBS1's ATM recruitment motif sequestered by binding to the regulatory RAD50 S site, necessitating a switch in the NBS1 C helix for ATM activation."
    explanation: >-
      Cryo-EM structures show that RAD50 directly gates ATM activation through its
      regulatory S site, giving a structural basis for why RAD50 lesions abolish ATM
      signalling even when the complex still assembles.
  downstream:
  - target: Impaired ATM activation and DNA damage signaling
    causal_link_type: DIRECT
    description: >-
      MRN is required to recruit and activate ATM at breaks; its failure blunts the
      ATM-dependent phosphorylation cascade.
  - target: Impaired DNA end resection and homologous recombination repair
    causal_link_type: DIRECT
    description: >-
      RAD50 gates MRE11 nuclease access, so RAD50 defects impair initiation of resection
      and homology-directed repair.
- name: Impaired ATM activation and DNA damage signaling
  biological_scale: MOLECULAR
  description: >-
    Radiation-induced activation of the ATM kinase and phosphorylation of its downstream
    substrates are markedly reduced in RAD50-deficient patient fibroblasts, phenocopying
    the signalling defect of ataxia-telangiectasia. Complementation with wild-type RAD50
    restores ATM activation, establishing the dependency.
  biological_processes:
  - preferred_term: DNA damage checkpoint signaling
    modifier: DECREASED
    term:
      id: GO:0000077
      label: DNA damage checkpoint signaling
  - preferred_term: DNA damage response
    modifier: ABNORMAL
    term:
      id: GO:0006974
      label: DNA damage response
  evidence:
  - reference: PMID:19409520
    reference_title: Human RAD50 deficiency in a Nijmegen breakage syndrome-like disorder.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "impaired radiation-induced activation of and downstream signaling through the ATM protein, which is defective in the human genetic disorder ataxia-telangiectasia"
    explanation: Directly documents impaired ATM activation and downstream signalling in patient cells.
  - reference: PMID:37794136
    reference_title: Bone Marrow Failure and Immunodeficiency Associated with Human RAD50 Variants.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "DNA damage-induced activation of the ATM kinase was markedly decreased, which was restored by the expression of wild-type (WT) RAD50."
    explanation: >-
      Complementation with wild-type RAD50 rescues ATM activation, establishing that the
      signalling defect is directly caused by the RAD50 lesion.
  - reference: PMID:32212377
    reference_title: "Human RAD50 deficiency: Confirmation of a distinctive phenotype."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "provided evidence for a markedly reduced radiation-induced AT-mutated signaling"
    explanation: Independent confirmation of reduced radiation-induced ATM signalling.
  downstream:
  - target: Cell-cycle checkpoint failure and radioresistant DNA synthesis
    causal_link_type: DIRECT
    description: >-
      Loss of ATM-dependent signalling disables the G1/S and intra-S checkpoints that
      normally suppress DNA synthesis after irradiation.
- name: Impaired DNA end resection and homologous recombination repair
  biological_scale: MOLECULAR
  description: >-
    RAD50 regulates MRE11-dependent 5'-3' end resection, the committed step of
    homology-directed repair, and also supports replication-fork function. The
    RAD50 E1035del coiled-coil allele demonstrates that this arm is genetically
    separable from ATM signalling, defining a separation-of-function mechanism within
    NBSLD.
  biological_processes:
  - preferred_term: double-strand break repair via homologous recombination
    modifier: DECREASED
    term:
      id: GO:0000724
      label: double-strand break repair via homologous recombination
  evidence:
  - reference: PMID:33378670
    reference_title: A Disease-Causing Single Amino Acid Deletion in the Coiled-Coil Domain of RAD50 Impairs MRE11 Complex Functions in Yeast and Humans.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "This mutation represents a human RAD50 separation-of-function mutation that impairs DNA repair, DNA replication, and DNA end resection without affecting ATM-dependent DNA damage response."
    explanation: >-
      Establishes an ATM-independent resection/repair arm of RAD50 pathogenesis and its
      genetic separability from the checkpoint-signalling arm.
  - reference: PMID:33378670
    reference_title: A Disease-Causing Single Amino Acid Deletion in the Coiled-Coil Domain of RAD50 Impairs MRE11 Complex Functions in Yeast and Humans.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Purified recombinant proteins indicate that RAD50E1035Δ impairs MRE11 nuclease activity."
    explanation: Biochemical demonstration that the RAD50 lesion acts by impairing MRE11 nuclease activity.
  downstream:
  - target: Chromosomal instability and cellular radiosensitivity
    causal_link_type: DIRECT
    description: >-
      Failure of homology-directed repair leaves double-strand breaks to be resolved by
      error-prone routes, generating breaks and rearrangements.
- name: Cell-cycle checkpoint failure and radioresistant DNA synthesis
  biological_scale: CELLULAR
  description: >-
    Patient fibroblasts fail to activate the G1/S checkpoint, continue DNA synthesis
    after irradiation (radioresistant DNA synthesis, RDS) and accumulate in G2. RDS is
    the key functional diagnostic readout of NBSLD, shared with ataxia-telangiectasia,
    NBS and ATLD.
  cell_types:
  - preferred_term: fibroblast
    term:
      id: CL:0000057
      label: fibroblast
  biological_processes:
  - preferred_term: mitotic intra-S DNA damage checkpoint signaling
    modifier: DECREASED
    term:
      id: GO:0031573
      label: mitotic intra-S DNA damage checkpoint signaling
  evidence:
  - reference: PMID:19409520
    reference_title: Human RAD50 deficiency in a Nijmegen breakage syndrome-like disorder.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "These cells were also impaired in G1/S cell-cycle-checkpoint activation and displayed radioresistant DNA synthesis and G2-phase accumulation."
    explanation: Directly documents checkpoint failure, RDS and G2 accumulation in patient cells.
  - reference: PMID:32212377
    reference_title: "Human RAD50 deficiency: Confirmation of a distinctive phenotype."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Using patient-derived primary fibroblasts, we could show abnormal radioresistant DNA synthesis confirming pathogenicity of the identified variant."
    explanation: Independent confirmation of radioresistant DNA synthesis in a second patient.
  downstream:
  - target: Chromosomal instability and cellular radiosensitivity
    causal_link_type: DIRECT
    description: >-
      Replicating through unrepaired damage without checkpoint arrest converts lesions
      into chromosomal breaks and rearrangements.
- name: Chromosomal instability and cellular radiosensitivity
  biological_scale: CELLULAR
  description: >-
    RAD50-deficient cells display spontaneous chromosomal instability and hypersensitivity
    to ionizing radiation. This is the cellular hallmark shared across the chromosomal
    instability syndromes and underlies the clinical recommendation to minimise
    radiation-based imaging.
  cell_types:
  - preferred_term: fibroblast
    term:
      id: CL:0000057
      label: fibroblast
  biological_processes:
  - preferred_term: DNA repair
    modifier: ABNORMAL
    term:
      id: GO:0006281
      label: DNA repair
  evidence:
  - reference: PMID:19409520
    reference_title: Human RAD50 deficiency in a Nijmegen breakage syndrome-like disorder.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Cells from the patient were characterized by chromosomal instability; radiosensitivity"
    explanation: Directly documents chromosomal instability and radiosensitivity in RAD50-deficient cells.
  - reference: PMID:19409520
    reference_title: Human RAD50 deficiency in a Nijmegen breakage syndrome-like disorder.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "The defective cellular phenotype was rescued by wild-type RAD50."
    explanation: >-
      Complementation rescue establishes that the cellular instability phenotype is caused
      by the RAD50 lesion rather than by an unlinked variant.
  downstream:
  - target: Genotoxic stress in proliferating progenitor pools
    causal_link_type: DIRECT
    description: >-
      Persistent genome instability is most consequential in tissues with high
      proliferative demand.
  - target: Increased sensitivity to ionizing radiation
    causal_link_type: DIRECT
    description: Defective double-strand break repair renders patient cells radiosensitive.
  - target: Chromosome breakage
    causal_link_type: DIRECT
    description: Unrepaired double-strand breaks manifest cytogenetically as chromosome breakage.
- name: Genotoxic stress in proliferating progenitor pools
  biological_scale: CELLULAR
  mechanism_confidence: PROVISIONAL
  description: >-
    Even subtle perturbation of MRN complex function generates severe genotoxic stress
    that is disproportionately borne by rapidly dividing progenitor compartments -
    neural progenitors during corticogenesis, somatic growth plates, and haematopoietic
    stem cells. This is the proposed convergence point linking a housekeeping DNA-repair
    defect to a selective growth, neurodevelopmental and marrow phenotype. The
    progenitor-attrition mechanism is directly demonstrated in Rad50(S/S) mice; its
    application to the human neurodevelopmental phenotype remains an inference.
  cell_types:
  - preferred_term: neural progenitor cell
    term:
      id: CL:0011020
      label: neural progenitor cell
  - preferred_term: hematopoietic stem cell
    term:
      id: CL:0000037
      label: hematopoietic stem cell
  evidence:
  - reference: PMID:12208847
    reference_title: Cancer predisposition and hematopoietic failure in Rad50(S/S) mice.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "The data indicate that even subtle perturbation of Mre11 complex functions results in severe genotoxic stress, and that the complex is critically important for homeostasis of proliferative tissues."
    explanation: >-
      Establishes in a hypomorphic Rad50 mouse that partial MRN perturbation selectively
      compromises proliferative tissue homeostasis via genotoxic stress.
  - reference: PMID:12208847
    reference_title: Cancer predisposition and hematopoietic failure in Rad50(S/S) mice.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Rad50(S/S) mice died with complete bone marrow depletion as a result of progressive hematopoietic stem cell failure."
    explanation: Demonstrates progressive haematopoietic stem cell attrition as the consequence of hypomorphic Rad50.
  downstream:
  - target: Microcephaly
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Depletion of the neural progenitor pool during corticogenesis is the inferred route
      to congenital microcephaly; the intermediate steps have not been demonstrated in
      human RAD50-deficient tissue.
    evidence:
    - reference: PMID:12208847
      reference_title: Cancer predisposition and hematopoietic failure in Rad50(S/S) mice.
      supports: PARTIAL
      evidence_source: MODEL_ORGANISM
      snippet: "The data indicate that even subtle perturbation of Mre11 complex functions results in severe genotoxic stress, and that the complex is critically important for homeostasis of proliferative tissues."
      explanation: >-
        Supports the general proliferative-tissue-homeostasis premise in mouse. It does NOT
        demonstrate the neural-progenitor route to microcephaly, which is why this edge is
        typed INDIRECT_UNKNOWN_INTERMEDIATES and the evidence is PARTIAL.
  - target: Intrauterine growth retardation
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: Reduced proliferative capacity across somatic tissues restricts prenatal growth.
    evidence:
    - reference: PMID:12208847
      reference_title: Cancer predisposition and hematopoietic failure in Rad50(S/S) mice.
      supports: PARTIAL
      evidence_source: MODEL_ORGANISM
      snippet: "We demonstrate here that hypomorphic Rad50 mutant mice (Rad50(S/S) mice) exhibited growth defects and cancer predisposition."
      explanation: >-
        Hypomorphic Rad50 produces growth defects in mouse, supporting the growth arm of the
        mechanism; the prenatal timing in humans is not established by this result.
  - target: Short stature
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: Continued restriction of proliferative growth produces postnatal short stature.
    evidence:
    - reference: PMID:12208847
      reference_title: Cancer predisposition and hematopoietic failure in Rad50(S/S) mice.
      supports: PARTIAL
      evidence_source: MODEL_ORGANISM
      snippet: "We demonstrate here that hypomorphic Rad50 mutant mice (Rad50(S/S) mice) exhibited growth defects and cancer predisposition."
      explanation: >-
        Supports growth restriction as a consequence of hypomorphic Rad50 in mouse; the
        human postnatal course is documented clinically on the phenotype record itself.
  - target: Mild intellectual disability
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      The same neural-progenitor attrition inferred to cause microcephaly is the presumed
      route to the accompanying mild, non-progressive cognitive impairment.
  - target: Bone marrow failure and B-lymphocyte deficiency
    causal_link_type: DIRECT
    description: >-
      In the marrow-failure arm, haematopoietic stem and B-lineage progenitors are the
      compartment that decompensates.
- name: Bone marrow failure and B-lymphocyte deficiency
  biological_scale: TISSUE
  description: >-
    In an allele-dependent subset of patients, RAD50 deficiency decompensates the
    haematopoietic and B-lineage compartments, producing bone marrow failure and B-cell
    immunodeficiency - the feature that makes NBSLD, in these patients, an inborn error
    of immunity rather than a purely dysmorphic/growth syndrome.
  cell_types:
  - preferred_term: hematopoietic stem cell
    term:
      id: CL:0000037
      label: hematopoietic stem cell
  - preferred_term: B cell
    term:
      id: CL:0000236
      label: B cell
  evidence:
  - reference: PMID:37794136
    reference_title: Bone Marrow Failure and Immunodeficiency Associated with Human RAD50 Variants.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "These findings indicate important roles of RAD50 in human bone marrow and immune cells."
    explanation: Establishes a RAD50-dependent requirement in human marrow and immune compartments.
  - reference: PMID:33378670
    reference_title: A Disease-Causing Single Amino Acid Deletion in the Coiled-Coil Domain of RAD50 Impairs MRE11 Complex Functions in Yeast and Humans.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Here, we identify a patient with bone marrow failure and developmental defects caused by biallelic RAD50 mutations."
    explanation: Independent report linking biallelic RAD50 mutations to bone marrow failure.
  downstream:
  - target: Bone marrow hypocellularity
    causal_link_type: DIRECT
    description: Haematopoietic stem cell failure manifests as marrow hypocellularity.
  - target: Decreased total B cell count
    causal_link_type: DIRECT
    description: The B-lineage compartment is selectively depleted.
mechanistic_hypotheses:
- hypothesis_group_id: allele_dependent_immunohematologic_arm
  hypothesis_label: Residual RAD50 function determines whether the immune/haematopoietic arm manifests
  status: EMERGING
  description: >-
    Reported RAD50 genotypes segregate into a "classic" arm with growth failure and
    microcephaly but preserved immunity, and an arm with bone marrow failure and B-cell
    immunodeficiency. The proposed explanation is that different alleles preserve
    different MRN sub-functions: the E1035del coiled-coil allele impairs end resection
    and replication while sparing ATM signalling, whereas the p.Arg83His/p.Glu485Ter
    genotype preserves complex assembly but abolishes ATM activation. Which sub-function
    is retained is hypothesised to determine whether the haematopoietic/B-cell
    compartment decompensates. This mapping is inferred from a handful of patients and
    has not been tested systematically.
  evidence:
  - reference: PMID:33378670
    reference_title: A Disease-Causing Single Amino Acid Deletion in the Coiled-Coil Domain of RAD50 Impairs MRE11 Complex Functions in Yeast and Humans.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "This mutation represents a human RAD50 separation-of-function mutation that impairs DNA repair, DNA replication, and DNA end resection without affecting ATM-dependent DNA damage response."
    explanation: Demonstrates that RAD50 alleles can dissociate MRN sub-functions, the premise of the hypothesis.
  - reference: PMID:41031707
    reference_title: RAD50 missense variants differentially affect the DNA damage response and mitotic progression.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Eight missense variants, all capable of forming an MRN complex, supported the DNA damage response and mitotic features to different extents, indicating these functions are separable."
    explanation: >-
      Demonstrates that RAD50 variants separate the damage-response and mitotic functions.
      Note the variants tested were cancer-related RAD50 missense alleles, not NBSLD patient
      alleles, so this supports the general principle of functional separability rather than
      the specific classic-versus-marrow-failure split.
  - reference: PMID:41031707
    reference_title: RAD50 missense variants differentially affect the DNA damage response and mitotic progression.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Functional heterogeneity of RAD50 variants could contribute to clinical variability."
    explanation: >-
      Systematic functional dissection of cancer-related RAD50 missense variants explicitly
      proposes allele-level functional heterogeneity as a source of clinical variability -
      the premise this hypothesis extends to the NBSLD allelic spectrum, which the study
      itself did not test.
phenotypes:
- name: Microcephaly
  category: Neurological
  diagnostic: true
  frequency: VERY_FREQUENT
  description: >-
    Severe microcephaly, present congenitally, is a cardinal and near-invariant feature
    of NBSLD and one of the features that originally prompted a clinical diagnosis of
    Nijmegen breakage syndrome in the index patient.
  phenotype_term:
    preferred_term: Microcephaly
    term:
      id: HP:0000252
      label: Microcephaly
  evidence:
  - reference: PMID:19409520
    reference_title: Human RAD50 deficiency in a Nijmegen breakage syndrome-like disorder.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Here, we report on a patient previously diagnosed as probably having NBS, with microcephaly, mental retardation, 'bird-like' face, and short stature."
    explanation: Directly documents microcephaly in the index RAD50-deficient patient.
  - reference: PMID:41798197
    reference_title: Novel RAD50 variants lead to Nijmegen Breakage Syndrome-like disorder and unplanned recombinant human growth hormone treatment response.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Human RAD50 gene mutations cause Nijmegen Breakage Syndrome-like disease, characterized by severe prenatal and postpartum growth retardation and microcephaly."
    explanation: >-
      Characterises microcephaly as a defining feature of the disorder, supporting the
      VERY_FREQUENT band.
  - reference: PMID:41655867
    reference_title: "Expanding the mutational spectrum of RAD50: a case report of Nijmegen breakage syndrome-like disorder in a Chinese child."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "who presented with bilateral cryptorchidism, severe microcephaly, growth retardation, multiple café-au-lait macules, brachydactyly, and distinctive craniofacial features"
    explanation: Confirms severe microcephaly in an additional independently reported patient.
- name: Intrauterine growth retardation
  category: Growth
  description: >-
    Growth restriction in NBSLD begins prenatally, distinguishing it from postnatal-onset
    growth failure syndromes.
  phenotype_term:
    preferred_term: Intrauterine growth retardation
    term:
      id: HP:0001511
      label: Intrauterine growth retardation
  evidence:
  - reference: PMID:41798197
    reference_title: Novel RAD50 variants lead to Nijmegen Breakage Syndrome-like disorder and unplanned recombinant human growth hormone treatment response.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "characterized by severe prenatal and postpartum growth retardation and microcephaly"
    explanation: Directly documents prenatal (intrauterine) growth retardation as a defining feature.
- name: Postnatal growth retardation
  category: Growth
  description: >-
    Growth restriction continues after birth; in one reported patient height was -3.35 SD
    before growth hormone therapy.
  phenotype_term:
    preferred_term: Postnatal growth retardation
    term:
      id: HP:0008897
      label: Postnatal growth retardation
  evidence:
  - reference: PMID:41798197
    reference_title: Novel RAD50 variants lead to Nijmegen Breakage Syndrome-like disorder and unplanned recombinant human growth hormone treatment response.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The boy was born at full term, with substantial growth retardation from infancy to early childhood."
    explanation: Documents postnatal growth retardation from infancy in a reported NBSLD patient.
- name: Short stature
  category: Growth
  diagnostic: true
  frequency: VERY_FREQUENT
  description: >-
    Short stature is reported in essentially every molecularly confirmed NBSLD patient and
    is frequently the presenting complaint that triggers endocrine referral.
  phenotype_term:
    preferred_term: Short stature
    term:
      id: HP:0004322
      label: Short stature
  evidence:
  - reference: PMID:19409520
    reference_title: Human RAD50 deficiency in a Nijmegen breakage syndrome-like disorder.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "with microcephaly, mental retardation, 'bird-like' face, and short stature"
    explanation: Documents short stature in the index patient.
  - reference: PMID:32212377
    reference_title: "Human RAD50 deficiency: Confirmation of a distinctive phenotype."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "we report a long-term follow-up of an unrelated patient with facial dysmorphisms, microcephaly, skeletal features, and short stature"
    explanation: Confirms short stature in the second reported patient.
  - reference: PMID:37794136
    reference_title: Bone Marrow Failure and Immunodeficiency Associated with Human RAD50 Variants.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We report on a girl with microcephaly, mental retardation, bird-like face, short stature, bone marrow failure and B-cell immunodeficiency."
    explanation: Confirms short stature in a third independently reported patient.
  - reference: PMID:41798197
    reference_title: Novel RAD50 variants lead to Nijmegen Breakage Syndrome-like disorder and unplanned recombinant human growth hormone treatment response.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "intrauterine growth\nretardation; microcephaly at bi rth; short stature; progressive\nmicrocephaly; and speci ﬁc facial features."
    explanation: >-
      Frequency basis for VERY_FREQUENT: a cross-patient synthesis over the reported RAD50
      cohort ("Among patients with available data, the following characteristics were
      observed"), not a single case, listing short stature among the shared characteristics.
      Preferred over a 3/3 count derived from individual case reports because it is an
      explicit multi-patient statement. Snippet retains the source PDF's line breaks and
      ligature/spacing artifacts so it matches the cached body exactly.
- name: Mild intellectual disability
  category: Neurological
  frequency: VERY_FREQUENT
  description: >-
    Cognitive impairment in NBSLD is generally mild and, in the best-followed patients,
    non-progressive - a contrast with the progressive neurodegeneration of
    ataxia-telangiectasia-like disorder.
  phenotype_term:
    preferred_term: Mild intellectual disability
    term:
      id: HP:0001256
      label: Mild intellectual disability
  evidence:
  - reference: PMID:41655867
    reference_title: "Expanding the mutational spectrum of RAD50: a case report of Nijmegen breakage syndrome-like disorder in a Chinese child."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Mild intellectual impairment was confirmed on formal neurocognitive testing."
    explanation: Formal neurocognitive testing documenting mild intellectual impairment.
  - reference: PMID:19409520
    reference_title: Human RAD50 deficiency in a Nijmegen breakage syndrome-like disorder.
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: "with microcephaly, mental retardation, 'bird-like' face, and short stature"
    explanation: >-
      Documents intellectual disability in the index patient; the abstract does not grade
      severity, so this supports the phenotype but not specifically the "mild" qualifier.
  - reference: PMID:41798197
    reference_title: Novel RAD50 variants lead to Nijmegen Breakage Syndrome-like disorder and unplanned recombinant human growth hormone treatment response.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "They all exhibit normal\nsexual development and show no decline in nervous system; they\nonly demonstrate mild learning disabilities."
    explanation: >-
      Frequency basis for VERY_FREQUENT, and the warrant for the MILD qualifier: a
      cross-patient synthesis stating that the reported RAD50 patients "all" show no
      neurological decline and demonstrate "only" mild learning disabilities. This resolves
      the earlier gap where no source graded severity across patients. Snippet retains the
      source PDF line breaks so it matches the cached body exactly.
- name: Bird-like facies
  category: Craniofacial
  diagnostic: true
  description: >-
    A "bird-like" facial gestalt is a recurrent recognisable feature shared with Nijmegen
    breakage syndrome and is often what prompts genetic evaluation. In the individually
    described patients the craniofacial profile comprised a sloping forehead, midface
    prominence and a receding mandible; those are per-patient observations rather than a
    definition of the bird-like gestalt, and are curated separately as Sloping forehead
    and Retrognathia.
  phenotype_term:
    preferred_term: Bird-like facies
    term:
      id: HP:0000320
      label: Bird-like facies
  evidence:
  - reference: PMID:19409520
    reference_title: Human RAD50 deficiency in a Nijmegen breakage syndrome-like disorder.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "with microcephaly, mental retardation, 'bird-like' face, and short stature"
    explanation: Directly documents bird-like facies in the index patient.
  - reference: PMID:37794136
    reference_title: Bone Marrow Failure and Immunodeficiency Associated with Human RAD50 Variants.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We report on a girl with microcephaly, mental retardation, bird-like face, short stature, bone marrow failure and B-cell immunodeficiency."
    explanation: Confirms bird-like facies in an independently reported patient.
- name: Sloping forehead
  category: Craniofacial
  description: >-
    A sloping forehead, together with midface prominence and a receding mandible, forms
    the distinctive craniofacial profile of NBSLD.
  phenotype_term:
    preferred_term: Sloping forehead
    term:
      id: HP:0000340
      label: Sloping forehead
  evidence:
  - reference: PMID:41655867
    reference_title: "Expanding the mutational spectrum of RAD50: a case report of Nijmegen breakage syndrome-like disorder in a Chinese child."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "including a sloping forehead, midface prominence, and receding mandible"
    explanation: Directly documents a sloping forehead as part of the craniofacial phenotype.
- name: Cafe-au-lait spot
  category: Dermatologic
  description: >-
    Multiple cafe-au-lait macules have been reported in NBSLD, a pigmentary feature that
    also occurs in other chromosomal instability syndromes and can prompt consideration of
    constitutional mismatch repair deficiency or neurofibromatosis type 1.
  phenotype_term:
    preferred_term: Cafe-au-lait spot
    term:
      id: HP:0000957
      label: Cafe-au-lait spot
  evidence:
  - reference: PMID:41655867
    reference_title: "Expanding the mutational spectrum of RAD50: a case report of Nijmegen breakage syndrome-like disorder in a Chinese child."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "severe microcephaly, growth retardation, multiple café-au-lait macules, brachydactyly"
    explanation: Directly documents multiple cafe-au-lait macules in a reported NBSLD patient.
- name: Brachydactyly
  category: Skeletal
  description: Digital shortening is part of the reported skeletal phenotype of NBSLD.
  phenotype_term:
    preferred_term: Brachydactyly
    term:
      id: HP:0001156
      label: Brachydactyly
  evidence:
  - reference: PMID:41655867
    reference_title: "Expanding the mutational spectrum of RAD50: a case report of Nijmegen breakage syndrome-like disorder in a Chinese child."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "multiple café-au-lait macules, brachydactyly, and distinctive craniofacial features"
    explanation: Directly documents brachydactyly in a reported NBSLD patient.
- name: Cryptorchidism
  category: Genitourinary
  description: >-
    Bilateral cryptorchidism was reported in a male NBSLD patient, expanding the
    recognised phenotypic spectrum.
  phenotype_term:
    preferred_term: Cryptorchidism
    term:
      id: HP:0000028
      label: Cryptorchidism
  evidence:
  - reference: PMID:41655867
    reference_title: "Expanding the mutational spectrum of RAD50: a case report of Nijmegen breakage syndrome-like disorder in a Chinese child."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We report a 6-year-old Chinese boy, who presented with bilateral cryptorchidism, severe microcephaly, growth retardation"
    explanation: Directly documents bilateral cryptorchidism in a reported NBSLD patient.
- name: Chromosome breakage
  category: Laboratory
  diagnostic: true
  description: >-
    Spontaneous chromosomal instability in patient cells is a defining cytogenetic
    laboratory feature and the basis of the "chromosomal instability syndrome"
    classification. As with radiosensitivity, the cytogenetic finding is genotype-dependent
    and not uniformly present - a normal karyotype has been reported alongside abnormal
    radioresistant DNA synthesis - so a normal breakage study does not exclude the
    diagnosis.
  phenotype_term:
    preferred_term: Chromosome breakage
    term:
      id: HP:0040012
      label: Chromosome breakage
  evidence:
  - reference: PMID:19409520
    reference_title: Human RAD50 deficiency in a Nijmegen breakage syndrome-like disorder.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Cells from the patient were characterized by chromosomal instability; radiosensitivity"
    explanation: Directly documents chromosomal instability in RAD50-deficient patient cells.
  - reference: PMID:41655867
    reference_title: "Expanding the mutational spectrum of RAD50: a case report of Nijmegen breakage syndrome-like disorder in a Chinese child."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Nijmegen breakage syndrome-like disorder (NBSLD) is a rare chromosomal instability syndrome caused by biallelic pathogenic variants in RAD50"
    explanation: Classifies NBSLD as a chromosomal instability syndrome.
- name: Increased sensitivity to ionizing radiation
  category: Laboratory
  diagnostic: true
  description: >-
    Cellular radiosensitivity reflects defective double-strand break repair and is the
    basis for the clinical recommendation to prefer MRI/ultrasound over CT and plain
    radiography. Radiosensitivity is not uniform across genotypes - in one patient with
    preserved MRN complex formation it was inconspicuous by colony formation assay.
  phenotype_term:
    preferred_term: Increased sensitivity to ionizing radiation
    term:
      id: HP:0011133
      label: Increased sensitivity to ionizing radiation
  evidence:
  - reference: PMID:19409520
    reference_title: Human RAD50 deficiency in a Nijmegen breakage syndrome-like disorder.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Cells from the patient were characterized by chromosomal instability; radiosensitivity"
    explanation: Directly documents cellular radiosensitivity in the index patient.
  - reference: PMID:37794136
    reference_title: Bone Marrow Failure and Immunodeficiency Associated with Human RAD50 Variants.
    supports: PARTIAL
    evidence_source: IN_VITRO
    snippet: "Radiosensitivity appeared inconspicuous in the patient-derived cell line as assessed by colony formation assay."
    explanation: >-
      Qualifies the phenotype: radiosensitivity is genotype-dependent and was not
      detectable by colony formation assay in this patient, so a normal assay does not
      exclude NBSLD.
- name: Bone marrow hypocellularity
  category: Hematologic
  subtype: NBSLD with bone marrow failure
  description: >-
    Bone marrow failure occurs in an allele-dependent subset of NBSLD patients and is the
    principal determinant of prognosis in that group.
  phenotype_term:
    preferred_term: Bone marrow hypocellularity
    term:
      id: HP:0005528
      label: Bone marrow hypocellularity
  evidence:
  - reference: PMID:37794136
    reference_title: Bone Marrow Failure and Immunodeficiency Associated with Human RAD50 Variants.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "RAD50 deficiency/NBSLD can manifest as a distinct inborn error of immunity characterized by bone marrow failure and B-cell immunodeficiency."
    explanation: Directly documents bone marrow failure as part of the NBSLD spectrum.
  - reference: PMID:33378670
    reference_title: A Disease-Causing Single Amino Acid Deletion in the Coiled-Coil Domain of RAD50 Impairs MRE11 Complex Functions in Yeast and Humans.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Here, we identify a patient with bone marrow failure and developmental defects caused by biallelic RAD50 mutations."
    explanation: Independent report of bone marrow failure in a biallelic RAD50 patient.
- name: Decreased total B cell count
  category: Immunologic
  subtype: NBSLD with bone marrow failure
  description: >-
    B-cell immunodeficiency accompanies bone marrow failure in the severe arm of the
    RAD50-deficiency spectrum.
  phenotype_term:
    preferred_term: Decreased total B cell count
    term:
      id: HP:0010976
      label: Decreased total B cell count
  evidence:
  - reference: PMID:37794136
    reference_title: Bone Marrow Failure and Immunodeficiency Associated with Human RAD50 Variants.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We report on a girl with microcephaly, mental retardation, bird-like face, short stature, bone marrow failure and B-cell immunodeficiency."
    explanation: Directly documents B-cell immunodeficiency in a RAD50-deficient patient.
- name: Immunodeficiency
  category: Immunologic
  subtype: NBSLD with bone marrow failure
  description: >-
    Immunodeficiency is confined to the bone-marrow-failure arm of the RAD50 spectrum,
    where it takes the form of B-cell deficiency. It is deliberately scoped to that
    subtype rather than asserted for the disease as a whole, because its ABSENCE is the
    defining feature of classic NBSLD and of the MONDO/Orphanet disease definition.
  notes: >-
    Do not read this record as a disease-level assertion. In classic NBSLD immunodeficiency
    is absent: the index patient "never had severe infections, had normal immunoglobulin
    levels, and did not develop lymphoid malignancy up to age 23 years" (PMID:19409520),
    which is precisely what separates NBSLD from NBN-related Nijmegen breakage syndrome.
    That contrast is recorded on the Classic NBSLD subtype and on the Nijmegen breakage
    syndrome differential diagnosis.
  phenotype_term:
    preferred_term: Immunodeficiency
    term:
      id: HP:0002721
      label: Immunodeficiency
  evidence:
  - reference: PMID:37794136
    reference_title: Bone Marrow Failure and Immunodeficiency Associated with Human RAD50 Variants.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "RAD50 deficiency/NBSLD can manifest as a distinct inborn error of immunity characterized by bone marrow failure and B-cell immunodeficiency."
    explanation: >-
      Supports immunodeficiency specifically in the marrow-failure arm, establishing that
      the feature is allele-dependent rather than a disease-wide manifestation.
- name: Decreased total lymphocyte count
  category: Immunologic
  description: >-
    Borderline lymphopenia without overt immunodeficiency has been reported in a classic
    NBSLD patient, indicating that mild immunological abnormalities can occur even in the
    arm that lacks clinical immunodeficiency.
  phenotype_term:
    preferred_term: Decreased total lymphocyte count
    term:
      id: HP:0001888
      label: Decreased total lymphocyte count
  evidence:
  - reference: PMID:41655867
    reference_title: "Expanding the mutational spectrum of RAD50: a case report of Nijmegen breakage syndrome-like disorder in a Chinese child."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The immunological assessment revealed borderline lymphopenia without overt immunodeficiency."
    explanation: >-
      Documents borderline lymphopenia while explicitly excluding overt immunodeficiency in
      the same patient.
- name: Cataract
  category: Ocular
  subtype: NBSLD with bone marrow failure
  description: >-
    Early-onset cataract requiring surgery was documented at age 10 in the RAD50 E1035del
    patient, as part of a clinical picture the authors read as a DNA repair and/or telomere
    maintenance defect.
  phenotype_term:
    preferred_term: Cataract
    term:
      id: HP:0000518
      label: Cataract
  evidence:
  - reference: PMID:33378670
    reference_title: A Disease-Causing Single Amino Acid Deletion in the Coiled-Coil Domain of RAD50 Impairs MRE11 Complex Functions in Yeast and Humans.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "P1 also developed a cataract at 10 years of age that necessitated surgical intervention."
    explanation: Directly documents early-onset cataract requiring surgery in a RAD50-deficient patient.
- name: Thrombocytopenia
  category: Hematologic
  subtype: NBSLD with bone marrow failure
  description: Thrombocytopenia is part of the multilineage cytopenia of the marrow-failure arm.
  phenotype_term:
    preferred_term: Thrombocytopenia
    term:
      id: HP:0001873
      label: Thrombocytopenia
  evidence:
  - reference: PMID:33378670
    reference_title: A Disease-Causing Single Amino Acid Deletion in the Coiled-Coil Domain of RAD50 Impairs MRE11 Complex Functions in Yeast and Humans.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "P1's cell blood count revealed thrombocytopenia (platelet count of 113 G/L) associated with anemia (hemoglobin level of 10 g/dL) and neutropenia (neutrophil count of 1 G/L)"
    explanation: Quantified thrombocytopenia in the marrow-failure patient.
- name: Anemia
  category: Hematologic
  subtype: NBSLD with bone marrow failure
  description: Anemia accompanies thrombocytopenia and neutropenia in the marrow-failure arm.
  phenotype_term:
    preferred_term: Anemia
    term:
      id: HP:0001903
      label: Anemia
  evidence:
  - reference: PMID:33378670
    reference_title: A Disease-Causing Single Amino Acid Deletion in the Coiled-Coil Domain of RAD50 Impairs MRE11 Complex Functions in Yeast and Humans.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "P1's cell blood count revealed thrombocytopenia (platelet count of 113 G/L) associated with anemia (hemoglobin level of 10 g/dL) and neutropenia (neutrophil count of 1 G/L)"
    explanation: Quantified anemia in the marrow-failure patient.
- name: Decreased total neutrophil count
  category: Hematologic
  subtype: NBSLD with bone marrow failure
  description: Neutropenia completes the trilineage cytopenia of the marrow-failure arm.
  phenotype_term:
    preferred_term: Decreased total neutrophil count
    term:
      id: HP:0001875
      label: Decreased total neutrophil count
  evidence:
  - reference: PMID:33378670
    reference_title: A Disease-Causing Single Amino Acid Deletion in the Coiled-Coil Domain of RAD50 Impairs MRE11 Complex Functions in Yeast and Humans.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "P1's cell blood count revealed thrombocytopenia (platelet count of 113 G/L) associated with anemia (hemoglobin level of 10 g/dL) and neutropenia (neutrophil count of 1 G/L)"
    explanation: Quantified neutropenia in the marrow-failure patient.
- name: Aplastic anemia
  category: Hematologic
  subtype: NBSLD with bone marrow failure
  description: >-
    Marrow biopsy in the E1035del patient showed 15% cellularity without myelodysplastic
    features, which the authors read as aplastic anemia rather than a myelodysplastic
    process - a distinction that matters for management.
  phenotype_term:
    preferred_term: Aplastic anemia
    term:
      id: HP:0001915
      label: Aplastic anemia
  evidence:
  - reference: PMID:33378670
    reference_title: A Disease-Causing Single Amino Acid Deletion in the Coiled-Coil Domain of RAD50 Impairs MRE11 Complex Functions in Yeast and Humans.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Bone marrow smears and biopsies showed reduced cellularity (15%) without myelodysplastic features, consistent with aplastic anemia."
    explanation: >-
      Documents quantified marrow hypocellularity read as aplastic anemia, explicitly
      excluding myelodysplasia.
- name: Abnormality of skin pigmentation
  category: Dermatologic
  subtype: NBSLD with bone marrow failure
  description: >-
    Part of a dyskeratosis-congenita-like mucocutaneous triad (skin pigmentation, nail
    dysplasia, leukoplakia) reported in the marrow-failure patient. The triad is what drives
    the dyskeratosis congenita differential in this arm.
  phenotype_term:
    preferred_term: Abnormality of skin pigmentation
    term:
      id: HP:0001000
      label: Abnormality of skin pigmentation
  evidence:
  - reference: PMID:33378670
    reference_title: A Disease-Causing Single Amino Acid Deletion in the Coiled-Coil Domain of RAD50 Impairs MRE11 Complex Functions in Yeast and Humans.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "physical examination of P1 revealed failure to thrive (height of 108.5 cm, <3rd percentile; weight of 17.2 kg, <3rd percentile), skin pigmentation, nail dysplasia, leukoplakia, dental loss, microcephaly"
    explanation: Documents abnormal skin pigmentation as part of the mucocutaneous triad.
- name: Nail dysplasia
  category: Dermatologic
  subtype: NBSLD with bone marrow failure
  description: Second component of the dyskeratosis-congenita-like mucocutaneous triad.
  phenotype_term:
    preferred_term: Nail dysplasia
    term:
      id: HP:0002164
      label: Nail dysplasia
  evidence:
  - reference: PMID:33378670
    reference_title: A Disease-Causing Single Amino Acid Deletion in the Coiled-Coil Domain of RAD50 Impairs MRE11 Complex Functions in Yeast and Humans.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "skin pigmentation, nail dysplasia, leukoplakia, dental loss, microcephaly"
    explanation: Documents nail dysplasia in the marrow-failure patient.
- name: Oral leukoplakia
  category: Dermatologic
  subtype: NBSLD with bone marrow failure
  description: Third component of the dyskeratosis-congenita-like mucocutaneous triad.
  phenotype_term:
    preferred_term: Oral leukoplakia
    term:
      id: HP:0002745
      label: Oral leukoplakia
  evidence:
  - reference: PMID:33378670
    reference_title: A Disease-Causing Single Amino Acid Deletion in the Coiled-Coil Domain of RAD50 Impairs MRE11 Complex Functions in Yeast and Humans.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "skin pigmentation, nail dysplasia, leukoplakia, dental loss, microcephaly"
    explanation: Documents leukoplakia in the marrow-failure patient.
- name: Premature loss of teeth
  category: Craniofacial
  subtype: NBSLD with bone marrow failure
  description: Dental loss accompanied the mucocutaneous triad in the marrow-failure patient.
  phenotype_term:
    preferred_term: Premature loss of teeth
    term:
      id: HP:0006480
      label: Premature loss of teeth
  evidence:
  - reference: PMID:33378670
    reference_title: A Disease-Causing Single Amino Acid Deletion in the Coiled-Coil Domain of RAD50 Impairs MRE11 Complex Functions in Yeast and Humans.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "skin pigmentation, nail dysplasia, leukoplakia, dental loss, microcephaly"
    explanation: Documents dental loss in the marrow-failure patient.
- name: Failure to thrive
  category: Growth
  description: >-
    Failure to thrive with height and weight below the 3rd percentile was documented in the
    marrow-failure patient, consistent with the growth restriction seen across the spectrum.
  phenotype_term:
    preferred_term: Failure to thrive
    term:
      id: HP:0001508
      label: Failure to thrive
  evidence:
  - reference: PMID:33378670
    reference_title: A Disease-Causing Single Amino Acid Deletion in the Coiled-Coil Domain of RAD50 Impairs MRE11 Complex Functions in Yeast and Humans.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "physical examination of P1 revealed failure to thrive (height of 108.5 cm, <3rd percentile; weight of 17.2 kg, <3rd percentile)"
    explanation: Documents quantified failure to thrive in a RAD50-deficient patient.
- name: Micrognathia
  category: Craniofacial
  description: >-
    Micrognathia is independently reported alongside the receding-mandible description,
    forming part of the recurrent craniofacial profile.
  phenotype_term:
    preferred_term: Micrognathia
    term:
      id: HP:0000347
      label: Micrognathia
  evidence:
  - reference: PMID:41798197
    reference_title: Novel RAD50 variants lead to Nijmegen Breakage Syndrome-like disorder and unplanned recombinant human growth hormone treatment response.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "he had obvious facial deformities, including receding forehead, long and narrow nasal bridge, small and prominent mouth, smooth and short philtrum, and micrognathia"
    explanation: Directly documents micrognathia within the craniofacial phenotype.
- name: Retrognathia
  category: Craniofacial
  description: A receding mandible is part of the reported craniofacial profile of NBSLD.
  phenotype_term:
    preferred_term: Retrognathia
    term:
      id: HP:0000278
      label: Retrognathia
  evidence:
  - reference: PMID:41655867
    reference_title: "Expanding the mutational spectrum of RAD50: a case report of Nijmegen breakage syndrome-like disorder in a Chinese child."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "including a sloping forehead, midface prominence, and receding mandible"
    explanation: Directly documents a receding mandible as part of the craniofacial phenotype.
genetic:
- name: RAD50
  association: >-
    Causal biallelic hypomorphic/loss-of-function variants; complete RAD50 loss is not
    compatible with viability, so patients are compound heterozygous or homozygous for
    partial-function alleles.
  relationship_type: CAUSATIVE
  variant_origin: GERMLINE
  gene_term:
    preferred_term: RAD50
    term:
      id: hgnc:9816
      label: RAD50
  notes: >-
    Reported alleles span nonsense, frameshift, splice-disrupting, stop-codon-readthrough
    and in-frame single-residue deletion classes. Monoallelic RAD50 variants are a separate
    question (cancer susceptibility) and do not cause NBSLD.
  evidence:
  - reference: PMID:19409520
    reference_title: Human RAD50 deficiency in a Nijmegen breakage syndrome-like disorder.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In conclusion, we have identified and characterized a patient with a RAD50 deficiency that results in a clinical phenotype that can be classified as an NBS-like disorder (NBSLD)."
    explanation: Establishes RAD50 as the causal gene for NBSLD.
  - reference: PMID:41655867
    reference_title: "Expanding the mutational spectrum of RAD50: a case report of Nijmegen breakage syndrome-like disorder in a Chinese child."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "caused by biallelic pathogenic variants in RAD50, which is a key component of the MRE11-RAD50-NBS1 (MRN) complex involved in DNA double-strand break repair"
    explanation: Confirms biallelic RAD50 variants as the molecular cause and situates RAD50 in the MRN complex.
  - reference: PMID:19409520
    reference_title: Human RAD50 deficiency in a Nijmegen breakage syndrome-like disorder.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "To date, no disease due to RAD50 deficiency has been described."
    explanation: >-
      Records that this report established the gene-disease relationship for RAD50, which
      had no prior disease association.
variants:
- name: RAD50 index-patient compound heterozygous genotype (Waltes 2009)
  description: >-
    The defining genotype of the first molecularly confirmed NBSLD patient. The published
    abstract records only that the patient was compound heterozygous for two RAD50
    mutations producing low levels of unstable protein; the specific HGVS descriptions are
    in the full text and are deliberately not reproduced here, since no verified
    abstract-level snippet states them.
  gene:
    preferred_term: RAD50
    term:
      id: hgnc:9816
      label: RAD50
  clinical_significance: PATHOGENIC
  evidence:
  - reference: PMID:19409520
    reference_title: Human RAD50 deficiency in a Nijmegen breakage syndrome-like disorder.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We found that she is compound heterozygous for mutations in the RAD50 gene that give rise to low levels of unstable RAD50 protein."
    explanation: >-
      Documents the compound heterozygous genotype and its protein-level consequence in the
      index patient, without specifying the individual alleles.
- name: RAD50 c.2524G>A (p.Met800Phefs*7 / p.Val842Ile)
  description: >-
    Homozygous variant at the last base of exon 15 in the second reported NBSLD patient;
    induces aberrant splicing with predominantly premature truncation.
  gene:
    preferred_term: RAD50
    term:
      id: hgnc:9816
      label: RAD50
  clinical_significance: PATHOGENIC
  evidence:
  - reference: PMID:32212377
    reference_title: "Human RAD50 deficiency: Confirmation of a distinctive phenotype."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "We could show that this variant, c.2524G > A in exon 15 of the RAD50 gene, induces aberrant splicing of RAD50 mRNA mainly leading to premature protein truncation and thereby, most likely, to loss of RAD50 function."
    explanation: Documents the variant and its splicing/loss-of-function consequence.
- name: RAD50 p.Glu1035del (E1035del)
  description: >-
    In-frame deletion of a single residue in the heptad repeats of the RAD50 coiled-coil
    domain; a separation-of-function allele that impairs MRE11 nuclease activity, DNA end
    resection, repair and replication while leaving ATM-dependent signalling intact.
    Reported in trans with a null allele in a patient with bone marrow failure.
  gene:
    preferred_term: RAD50
    term:
      id: hgnc:9816
      label: RAD50
  clinical_significance: PATHOGENIC
  evidence:
  - reference: PMID:33378670
    reference_title: A Disease-Causing Single Amino Acid Deletion in the Coiled-Coil Domain of RAD50 Impairs MRE11 Complex Functions in Yeast and Humans.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "One of the mutations creates a null allele, whereas the other (RAD50E1035Δ) leads to the loss of a single residue in the heptad repeats within the RAD50 coiled-coil domain."
    explanation: Defines the allele and its position within the coiled-coil heptad repeats.
- name: RAD50 p.Arg83His and p.Glu485Ter
  description: >-
    Compound heterozygous genotype in the bone-marrow-failure/immunodeficiency patient.
    RAD50 expression and MRN complex formation were preserved, yet ATM activation failed;
    the p.Arg83His missense allele failed to rescue the mitotic defect in complementation,
    and the p.Glu485Ter nonsense allele produced in-frame skipping of exon 10.
  gene:
    preferred_term: RAD50
    term:
      id: hgnc:9816
      label: RAD50
  clinical_significance: PATHOGENIC
  evidence:
  - reference: PMID:37794136
    reference_title: Bone Marrow Failure and Immunodeficiency Associated with Human RAD50 Variants.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Compound heterozygosity for two variants in the RAD50 gene (p.Arg83His and p.Glu485Ter) was identified in this patient."
    explanation: Identifies the causal genotype in the marrow-failure patient.
  - reference: PMID:37794136
    reference_title: Bone Marrow Failure and Immunodeficiency Associated with Human RAD50 Variants.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "The RAD50R83H missense substitution did not rescue the mitotic defect in complementation experiments using RAD50-deficient fibroblasts, whereas RAD50WT did."
    explanation: Functional complementation evidence that p.Arg83His is a loss-of-function allele.
- name: RAD50 c.2165_2166insT (p.Lys722Asnfs*6) and c.3752+4_3752+7dup
  description: >-
    Compound heterozygous genotype in a Chinese patient; the paternal frameshift is
    truncating and the maternal splice-region duplication was shown by minigene assay to
    disrupt splicing with intron retention and a premature stop codon.
  gene:
    preferred_term: RAD50
    term:
      id: hgnc:9816
      label: RAD50
  clinical_significance: PATHOGENIC
  evidence:
  - reference: PMID:41655867
    reference_title: "Expanding the mutational spectrum of RAD50: a case report of Nijmegen breakage syndrome-like disorder in a Chinese child."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "a paternally inherited frameshift variant c.2165_2166insT (p.Lys722Asnfs*6) and a maternally inherited splice-site variant c.3752 + 4_3752 + 7dup"
    explanation: Identifies both alleles and their parental origin.
  - reference: PMID:41655867
    reference_title: "Expanding the mutational spectrum of RAD50: a case report of Nijmegen breakage syndrome-like disorder in a Chinese child."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "The minigene splicing assay revealed that the latter disrupts normal splicing, leading to partial intron retention and a premature stop codon (p.Ile1252*)."
    explanation: Functional splicing evidence supporting pathogenicity of the splice-region allele.
- name: RAD50 p.His1269Argfs*2 and p.Ser844Asn
  description: >-
    Two novel variants identified by trio whole-exome sequencing in a boy treated with
    growth hormone before genetic diagnosis; the frameshift allele markedly impairs RAD50
    protein expression or stability on Western blot.
  gene:
    preferred_term: RAD50
    term:
      id: hgnc:9816
      label: RAD50
  clinical_significance: UNCERTAIN_SIGNIFICANCE
  evidence:
  - reference: PMID:41798197
    reference_title: Novel RAD50 variants lead to Nijmegen Breakage Syndrome-like disorder and unplanned recombinant human growth hormone treatment response.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Two novel variants (p.His1269Argfs2 and p.Ser844Asn) were identified in the RAD50 gene."
    explanation: Identifies the two novel alleles in this patient.
  - reference: PMID:41798197
    reference_title: Novel RAD50 variants lead to Nijmegen Breakage Syndrome-like disorder and unplanned recombinant human growth hormone treatment response.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Western blotting revealed the presence of the Flag-tag and EGFP in RAD50-wt, but not in RAD50-mut (p.His1269Argfs2), indicating the frameshift mutation may markedly impair RAD50 protein expression or stability."
    explanation: Functional evidence that the frameshift allele destabilises RAD50 protein.
diagnosis:
- name: Whole-exome sequencing
  description: >-
    Essentially every reported NBSLD patient has been solved by exome sequencing, usually
    trio-based, because the clinical presentation overlaps NBS, ATLD and other
    microcephaly-growth-failure syndromes.
  presence: Identification of biallelic pathogenic RAD50 variants confirms the diagnosis.
  diagnosis_term:
    preferred_term: molecular genetic testing
    term:
      id: NCIT:C19770
      label: Molecular Analysis
    qualifiers:
    - predicate:
        preferred_term: has participant
        term:
          id: RO:0000057
          label: has participant
      value:
        preferred_term: RAD50
        term:
          id: hgnc:9816
          label: RAD50
  evidence:
  - reference: PMID:41655867
    reference_title: "Expanding the mutational spectrum of RAD50: a case report of Nijmegen breakage syndrome-like disorder in a Chinese child."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Whole-exome sequencing (WES) identified compound heterozygosity for two variants in RAD50 (NM_005732.3)"
    explanation: Documents WES as the diagnostic route to a molecular NBSLD diagnosis.
  - reference: PMID:37794136
    reference_title: Bone Marrow Failure and Immunodeficiency Associated with Human RAD50 Variants.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We searched for candidate gene by whole-exome sequencing and analyzed the cellular phenotype of patient-derived fibroblasts using immunoblotting, radiation sensitivity assays and lentiviral complementation experiments."
    explanation: Documents the WES-plus-functional-assay diagnostic workflow used for NBSLD.
- name: Radioresistant DNA synthesis assay in patient fibroblasts
  description: >-
    Functional demonstration that DNA synthesis is not suppressed after irradiation.
    Radioresistant DNA synthesis is the key functional confirmation of pathogenicity for
    candidate RAD50 variants, though it is shared with ataxia-telangiectasia, NBS and ATLD
    and is therefore not RAD50-specific on its own.
  presence: Abnormal (radioresistant) DNA synthesis supports a DNA damage response defect.
  evidence:
  - reference: PMID:32212377
    reference_title: "Human RAD50 deficiency: Confirmation of a distinctive phenotype."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Using patient-derived primary fibroblasts, we could show abnormal radioresistant DNA synthesis confirming pathogenicity of the identified variant."
    explanation: Directly documents RDS as the assay used to confirm variant pathogenicity.
- name: RAD50 immunoblotting in patient-derived fibroblasts
  description: >-
    Western blot for RAD50 (and its MRN partners) in patient fibroblasts is the most
    disease-specific functional readout, showing absent or markedly reduced protein.
    Interpretation caveat: some pathogenic genotypes preserve RAD50 expression and complex
    formation, so a normal blot does not exclude the diagnosis.
  presence: Absent or strongly reduced RAD50 protein supports the diagnosis.
  evidence:
  - reference: PMID:32212377
    reference_title: "Human RAD50 deficiency: Confirmation of a distinctive phenotype."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Immunoblotting experiments showed strongly reduced protein levels of RAD50 in the patient-derived fibroblasts"
    explanation: Documents immunoblotting as a confirmatory functional assay.
  - reference: PMID:37794136
    reference_title: Bone Marrow Failure and Immunodeficiency Associated with Human RAD50 Variants.
    supports: PARTIAL
    evidence_source: IN_VITRO
    snippet: "The expression of RAD50 protein and MRN complex formation was maintained in the cells derived from this patient."
    explanation: >-
      Records the interpretation caveat that preserved RAD50 expression does not exclude
      pathogenic RAD50 variants.
treatments:
- name: Recombinant human growth hormone
  description: >-
    Somatropin has been used off-label for the short stature of NBSLD. In the single
    reported experience, 5 years 9 months of therapy improved height from -3.35 SD to
    -1.28 SD with no tumour at 5-year post-discontinuation follow-up. IMPORTANT SAFETY
    CAVEAT - in that case growth hormone was started by junior physicians before any
    genetic evaluation; the authors emphasise that genetic evaluation should precede
    growth-promoting therapy in syndromic short stature, because growth hormone/IGF-1
    signalling is mitogenic and the underlying DNA repair deficiency may raise tumour
    risk. The evidence base is one patient.
  therapeutic_modality: PROTEIN_REPLACEMENT
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: somatropin
      term:
        id: NCIT:C837
        label: Somatropin
  target_phenotypes:
  - preferred_term: Short stature
    term:
      id: HP:0004322
      label: Short stature
  evidence:
  - reference: PMID:41798197
    reference_title: Novel RAD50 variants lead to Nijmegen Breakage Syndrome-like disorder and unplanned recombinant human growth hormone treatment response.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Although recombinant human growth hormone significantly improved the patient's growth rate (from -3.35 SD to -1.28 SD), these variants may serve as a potential molecular basis for Nijmegen Breakage Syndrome-like disease and could also increase the risk of tumor formation."
    explanation: >-
      Reports both the growth benefit and the explicit tumour-risk caution attached to it in
      the single documented NBSLD growth hormone experience.
  - reference: PMID:41798197
    reference_title: Novel RAD50 variants lead to Nijmegen Breakage Syndrome-like disorder and unplanned recombinant human growth hormone treatment response.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "At the age of 4.5 years, the child with syndromic short stature was prescribed recombinant human growth hormone for height correction by junior resident physicians, with no genetic evaluation performed prior to treatment."
    explanation: >-
      Documents the safety lesson that the therapy was given without prior genetic
      evaluation, which the report frames as the central cautionary finding.
- name: Surveillance-based supportive management
  description: >-
    In the absence of any disease-modifying therapy, reported NBSLD patients are managed
    with regular clinical surveillance and multidisciplinary supportive care. Because
    patient cells are radiosensitive, non-ionizing imaging (MRI, ultrasound) is preferred
    over CT and plain radiography where feasible.
  therapeutic_modality: OTHER
  treatment_term:
    preferred_term: supportive care
    term:
      id: NCIT:C15747
      label: Supportive Care
  evidence:
  - reference: PMID:41655867
    reference_title: "Expanding the mutational spectrum of RAD50: a case report of Nijmegen breakage syndrome-like disorder in a Chinese child."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "However, it is not presently required for this patient, who is managed with regular surveillance."
    explanation: Documents surveillance-based management as the current standard for an NBSLD patient.
  - reference: PMID:41798197
    reference_title: Novel RAD50 variants lead to Nijmegen Breakage Syndrome-like disorder and unplanned recombinant human growth hormone treatment response.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Due to the DNA damage repair defect, repeated X-ray or CT scans should be avoided, and MRI or ultrasound scans should be used instead."
    explanation: >-
      Directly supports the imaging-modality recommendation, which was previously asserted in
      the description without a supporting citation.
- name: Allogeneic hematopoietic stem cell transplantation
  description: >-
    HSCT has been proposed as a potential therapeutic option for DNA damage repair
    disorders and would be the standard consideration for the bone-marrow-failure arm of
    NBSLD. It has been raised but not required in the reported cases, so this is a
    proposed rather than established indication for this specific disorder.
  therapeutic_modality: CELL_THERAPY
  treatment_term:
    preferred_term: hematopoietic stem cell transplantation
    term:
      id: NCIT:C15431
      label: Hematopoietic Cell Transplantation
  target_phenotypes:
  - preferred_term: Bone marrow hypocellularity
    term:
      id: HP:0005528
      label: Bone marrow hypocellularity
  target_mechanisms:
  - target: Bone marrow failure and B-lymphocyte deficiency
    treatment_effect: INHIBITS
    description: >-
      Replacing the RAD50-deficient haematopoietic stem cell compartment with donor cells
      removes the failing compartment itself. It does not correct the RAD50 defect in
      neural, skeletal or other somatic tissue, so it addresses only the haematologic arm.
  evidence:
  - reference: PMID:41655867
    reference_title: "Expanding the mutational spectrum of RAD50: a case report of Nijmegen breakage syndrome-like disorder in a Chinese child."
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: "Allogeneic hematopoietic stem cell transplantation (HSCT) has been proposed as a potential therapeutic option for DNA damage repair disorders."
    explanation: >-
      Supports HSCT as a proposed option for DNA damage repair disorders; the same report
      makes clear it was not required in this patient, so the evidence is partial.
- name: Genetic counseling
  description: >-
    Autosomal recessive inheritance carries a 25% recurrence risk per pregnancy for carrier
    couples. Counseling should also cover the recommendation that molecular diagnosis
    precede any elective growth-promoting therapy.
  therapeutic_modality: BEHAVIORAL
  treatment_term:
    preferred_term: genetic counseling
    term:
      id: NCIT:C15240
      label: Genetic Counseling
  notes: >-
    No evidence item is attached. The 25% recurrence risk is a standard arithmetic
    consequence of the autosomal recessive inheritance documented elsewhere in this entry,
    not a claim quoted from any cited abstract, and no located source states it directly.
    Per the curation SOP the claim is kept as description rather than given a
    non-supporting citation. Carrier-level cancer-risk counseling is discussed separately
    under the rad50_heterozygous_carrier_cancer_risk discussion.
animal_models:
- species: Mus musculus
  genotype: Rad50(S/S)
  category: Hypomorphic knock-in
  description: >-
    Rad50 null mice are inviable; the hypomorphic Rad50(S/S) knock-in is the disease-relevant
    mouse model. It reproduces growth defects and genotoxic-stress-driven attrition of
    proliferative tissues, and dies of progressive haematopoietic stem cell failure. Note
    the divergence from classic human NBSLD: the mouse also shows cancer predisposition,
    whereas the longest-followed human patients have remained malignancy-free.
  genes:
  - preferred_term: RAD50
    term:
      id: hgnc:9816
      label: RAD50
  evidence:
  - reference: PMID:12208847
    reference_title: Cancer predisposition and hematopoietic failure in Rad50(S/S) mice.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "We demonstrate here that hypomorphic Rad50 mutant mice (Rad50(S/S) mice) exhibited growth defects and cancer predisposition."
    explanation: Documents the growth-defect and cancer phenotype of the hypomorphic mouse model.
  - reference: PMID:12208847
    reference_title: Cancer predisposition and hematopoietic failure in Rad50(S/S) mice.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Null mutants of each are inviable."
    explanation: >-
      Establishes that complete loss of MRN components is lethal, explaining why human
      patients necessarily carry hypomorphic alleles.
differential_diagnoses:
- name: Nijmegen breakage syndrome
  description: >-
    The NBN-related disorder that NBSLD phenocopies. Shares microcephaly, growth failure,
    bird-like facies, chromosomal instability and radiosensitivity.
  disease_term:
    preferred_term: Nijmegen breakage syndrome
    term:
      id: MONDO:0009623
      label: Nijmegen breakage syndrome
  distinguishing_features:
  - Combined cellular and humoral immunodeficiency with recurrent sinopulmonary infection is characteristic of NBS but absent in classic NBSLD.
  - Strong predisposition to lymphoid malignancy is characteristic of NBS; the longest-followed NBSLD patient was malignancy-free at 23 years.
  - Premature ovarian failure in females is characteristic of NBS and has not been reported in NBSLD.
  - Intellectual abilities decline over time in NBS, whereas NBSLD cognition has been stable and non-progressive.
  - Early growth deficiency improves with age in NBS, whereas NBSLD growth restriction persists into adulthood.
  - Causal gene is NBN in NBS versus RAD50 in NBSLD.
  evidence:
  - reference: PMID:19409520
    reference_title: Human RAD50 deficiency in a Nijmegen breakage syndrome-like disorder.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Here, we report on a patient previously diagnosed as probably having NBS, with microcephaly, mental retardation, 'bird-like' face, and short stature. At variance with this diagnosis, she never had severe infections, had normal immunoglobulin levels, and did not develop lymphoid malignancy up to age 23 years."
    explanation: >-
      Documents both the initial misdiagnosis as NBS and the specific features that
      distinguish NBSLD from it.
  - reference: PMID:20301355
    reference_title: Nijmegen Breakage Syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Nijmegen breakage syndrome (NBS) is characterized by progressive microcephaly, early growth deficiency that improves with age, recurrent respiratory infections, an increased risk for malignancy (primarily lymphoma), and premature ovarian failure in females."
    explanation: >-
      The GeneReviews chapter for NBS - the differential, not for NBSLD - supplies the
      authoritative NBS feature set. Recurrent respiratory infection, lymphoma risk and
      premature ovarian failure are absent from classic NBSLD, and NBS growth deficiency
      improves with age whereas NBSLD growth restriction persists.
  - reference: PMID:20301355
    reference_title: Nijmegen Breakage Syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Intellectual abilities tend to decline over time."
    explanation: >-
      Cognitive decline over time is characteristic of NBS, whereas NBSLD cognition has been
      described as stable and non-progressive - a further discriminator between the two.
- name: Ataxia-telangiectasia-like disorder
  description: >-
    The MRE11-related member of the MRN-complex disease triad. Shares radiosensitivity and
    defective ATM signalling with NBSLD.
  disease_term:
    preferred_term: ataxia-telangiectasia-like disorder 1
    term:
      id: MONDO:0024557
      label: ataxia-telangiectasia-like disorder 1
  distinguishing_features:
  - ATLD is dominated by progressive cerebellar ataxia and neurodegeneration, whereas NBSLD cognition has been non-progressive in the best-followed patients.
  - Severe congenital microcephaly with pre- and postnatal growth failure is the leading feature of NBSLD rather than of ATLD.
  - Causal gene is MRE11A in ATLD versus RAD50 in NBSLD.
  evidence:
  - reference: PMID:19409520
    reference_title: Human RAD50 deficiency in a Nijmegen breakage syndrome-like disorder.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Hypomorphic mutations in NBN (previously known as NBS1) and MRE11A give rise to the autosomal-recessive diseases Nijmegen breakage syndrome (NBS) and ataxia-telangiectasia-like disorder (ATLD), respectively."
    explanation: Establishes ATLD as the MRE11A-related sibling disorder within the MRN triad.
  - reference: PMID:38686720
    reference_title: "[Research Progress in the Roles of MRE11-RAD50-NBS1 Complex and Human Diseases]."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "we discuss the human diseases such as ataxia-telangiectasia-like disorder,Nijmegen breakage syndrome,and Nijmegen breakage syndrome-like disorder that are caused by dysfunctions in the MRN complex"
    explanation: >-
      A dedicated MRN review that treats ATLD, NBS and NBSLD as the three MRN-complex
      disorders, supporting the triad framing on which this differential rests.
- name: Ataxia-telangiectasia
  description: >-
    The ATM-related disorder whose cellular phenotype NBSLD closely mimics - impaired ATM
    signalling, radioresistant DNA synthesis and radiosensitivity are shared.
  disease_term:
    preferred_term: ataxia telangiectasia
    term:
      id: MONDO:0008840
      label: ataxia telangiectasia
  distinguishing_features:
  - Progressive cerebellar ataxia and oculocutaneous telangiectasia characterise A-T and are not features of NBSLD.
  - The primary lesion is in ATM itself in A-T, versus upstream MRN/RAD50 in NBSLD.
  evidence:
  - reference: PMID:19409520
    reference_title: Human RAD50 deficiency in a Nijmegen breakage syndrome-like disorder.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "impaired radiation-induced activation of and downstream signaling through the ATM protein, which is defective in the human genetic disorder ataxia-telangiectasia"
    explanation: >-
      Documents the shared ATM-signalling defect that makes A-T the key cellular-phenotype
      differential.
- name: Dyskeratosis congenita
  description: >-
    Relevant specifically to the bone-marrow-failure arm. The E1035del patient presented
    with marrow failure plus the classic dyskeratosis congenita mucocutaneous triad - skin
    pigmentation, nail dysplasia and leukoplakia - which the authors read as suggesting a
    DNA repair and/or telomere maintenance defect. A telomere-biology disorder is therefore
    the leading alternative diagnosis in an NBSLD patient presenting this way.
  disease_term:
    preferred_term: dyskeratosis congenita
    term:
      id: MONDO:0015780
      label: dyskeratosis congenita
  distinguishing_features:
  - Severe congenital microcephaly with pre- and postnatal growth restriction is characteristic of NBSLD and not of dyskeratosis congenita.
  - Dyskeratosis congenita is caused by telomere-maintenance gene defects with short telomeres, whereas NBSLD is caused by biallelic RAD50 variants affecting DSB sensing.
  - Radioresistant DNA synthesis and impaired ATM activation point to NBSLD rather than a telomere-biology disorder.
  evidence:
  - reference: PMID:33378670
    reference_title: A Disease-Causing Single Amino Acid Deletion in the Coiled-Coil Domain of RAD50 Impairs MRE11 Complex Functions in Yeast and Humans.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Collectively, P1's clinical features were reminiscent of a defect in DNA repair and/or telomere maintenance"
    explanation: >-
      The authors explicitly flag telomere maintenance as the competing explanation for this
      presentation, which is what makes dyskeratosis congenita the relevant differential for
      the marrow-failure arm.
discussions:
- discussion_id: nbsld_cancer_risk_unknown
  kind: KNOWLEDGE_GAP
  status: OPEN
  prompt: >-
    Does RAD50 deficiency confer a cancer predisposition comparable to that of NBN-related
    Nijmegen breakage syndrome, or is the apparent absence of malignancy in NBSLD real?
  attaches_to:
  - pathophysiology#Chromosomal instability and cellular radiosensitivity
  rationale: >-
    No malignancy has been reported in the longest-followed NBSLD patients (index patient
    malignancy-free at 23 years; a growth-hormone-treated patient tumour-free at 5-year
    follow-up). But the total published cohort is fewer than ten patients with variable
    follow-up, and both the paralogous human diseases (NBS, ATLD) and the hypomorphic
    Rad50(S/S) mouse show clear cancer predisposition. Absence of evidence here is not
    evidence of absence, and case-report authors explicitly flag increased tumour risk when
    considering mitogenic therapy.
  proposed_experiments:
  - experiment_id: exp_nbsld_prospective_oncologic_registry
    name: International RAD50-deficiency registry with prospective oncologic follow-up
    description: >-
      Assemble all molecularly confirmed RAD50-deficient patients into a shared registry
      with standardised, prospective, lifelong cancer surveillance and a defined minimum
      follow-up, so that malignancy incidence can be estimated rather than inferred from
      scattered case reports of varying duration.
  - experiment_id: exp_nbsld_genotype_stratified_cancer_risk
    name: Genotype-stratified analysis of cancer incidence against residual RAD50 function
    description: >-
      Measure residual RAD50 function for each patient allele using the established
      lentiviral complementation assays (damage response, mitotic progression), then test
      whether malignancy occurrence tracks residual function - which would explain why the
      classic arm appears cancer-free while the mouse model is cancer-prone.
  evidence:
  - reference: PMID:41798197
    reference_title: Novel RAD50 variants lead to Nijmegen Breakage Syndrome-like disorder and unplanned recombinant human growth hormone treatment response.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "these variants may serve as a potential molecular basis for Nijmegen Breakage Syndrome-like disease and could also increase the risk of tumor formation"
    explanation: >-
      Authors of the only treated case explicitly raise unresolved tumour risk despite the
      absence of observed malignancy.
  - reference: PMID:41798197
    reference_title: Novel RAD50 variants lead to Nijmegen Breakage Syndrome-like disorder and unplanned recombinant human growth hormone treatment response.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "due to the rarity of cases and the short follow-up period, we cannot\nrule out the possibility that patients with NBSLD caused by RAD50\nmutations are at an increased risk of malignancy. Patients with\nNBSLD caused by RAD50 mutations should be regularly monitored\nfor tumor occurrence."
    explanation: >-
      States the knowledge gap directly in the authors' own words - rarity and short
      follow-up prevent excluding increased malignancy risk - and gives the resulting
      surveillance recommendation. This is the primary warrant for this discussion.
  - reference: PMID:12208847
    reference_title: Cancer predisposition and hematopoietic failure in Rad50(S/S) mice.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "hypomorphic Rad50 mutant mice (Rad50(S/S) mice) exhibited growth defects and cancer predisposition"
    explanation: >-
      The hypomorphic mouse model does show cancer predisposition, which is what makes the
      human observation surprising and the gap worth resolving.
- discussion_id: rad50_heterozygous_carrier_cancer_risk
  kind: INTERPRETATION
  status: OPEN
  prompt: >-
    What, if anything, should parents and other heterozygous RAD50 carriers identified
    through an NBSLD diagnosis be told about their own cancer risk?
  rationale: >-
    This is a carrier-level question, deliberately kept out of the disease's genetic record
    because it is not evidence about NBSLD itself. Monoallelic RAD50 loss-of-function is
    studied as a breast-cancer susceptibility allele, but the risk is not uniform across
    alleles: a Northern Finnish population-based study classified the recurrent founder
    allele RAD50 c.687delT as a moderate-risk allele, whereas broader analyses of
    heterozygous RAD50 pathogenic variants have not shown a consistent overall breast-cancer
    excess. Cascade testing after an NBSLD diagnosis will identify obligate carrier parents,
    so the scope and limits of that risk statement matter practically. Nothing here implies
    a cancer risk statement for the biallelic disease.
  evidence:
  - reference: PMID:40009290
    reference_title: Population-based study of recurrent DNA damage response gene variants in breast cancer cases.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "whereas CHEK2 c.1100delC, MCPH1 c.909_921del, and RAD50 c.687delT were moderate-risk alleles"
    explanation: >-
      Establishes moderate breast-cancer risk specifically for the recurrent RAD50 c.687delT
      allele in a Northern Finnish population-based case-control study; it does not
      generalise to all heterozygous RAD50 variants or to any population.
- discussion_id: rad50_mouse_human_mismatch
  kind: HUMAN_MODEL_MISMATCH
  status: OPEN
  prompt: >-
    Does the hypomorphic Rad50(S/S) mouse faithfully model classic human NBSLD, given that
    the mouse dies of bone marrow failure with cancer predisposition while classic human
    NBSLD patients have preserved immunity, no malignancy and a stable course?
  attaches_to:
  - pathophysiology#Genotoxic stress in proliferating progenitor pools
  rationale: >-
    The progenitor-attrition mechanism invoked for human growth failure and microcephaly is
    demonstrated principally in Rad50(S/S) mice, but that model's dominant outcomes -
    lethal haematopoietic failure and tumours - correspond to the minority bone-marrow-failure
    arm of the human spectrum, not the classic arm. Conversely, no mouse model reproduces
    the severe congenital microcephaly that defines human NBSLD. Because Rad50 nulls are
    embryonically lethal, viable models necessarily carry particular hypomorphic alleles
    whose residual activity may not correspond to any human genotype, so mechanistic
    inferences drawn from the mouse for the human neurodevelopmental phenotype have
    uncertain translational validity.
  proposed_experiments:
  - experiment_id: exp_rad50_humanised_allele_knockin_mice
    name: Knock-in mice carrying human NBSLD RAD50 alleles
    description: >-
      Generate mice bearing the specific human alleles (E1035del, p.Arg83His, the exon-15
      splice allele) and compare cortical progenitor dynamics, body growth, haematopoiesis
      and tumour incidence, to test whether particular human alleles reproduce the classic
      growth/microcephaly arm rather than the murine marrow-failure/cancer phenotype.
  - experiment_id: exp_rad50_cerebral_organoids
    name: RAD50-deficient human cerebral organoids
    description: >-
      Derive iPSC cerebral organoids from RAD50-deficient patients and quantify neural
      progenitor proliferation, premature differentiation and apoptosis, mirroring the
      organoid work already done for NBN-related Nijmegen breakage syndrome, to test the
      progenitor-attrition route to microcephaly directly in human tissue.
  evidence:
  - reference: PMID:12208847
    reference_title: Cancer predisposition and hematopoietic failure in Rad50(S/S) mice.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Rad50(S/S) mice died with complete bone marrow depletion as a result of progressive hematopoietic stem cell failure."
    explanation: >-
      The mouse's lethal marrow phenotype is the specific outcome that does not match classic
      human NBSLD.
  - reference: PMID:19409520
    reference_title: Human RAD50 deficiency in a Nijmegen breakage syndrome-like disorder.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "she never had severe infections, had normal immunoglobulin levels, and did not develop lymphoid malignancy up to age 23 years"
    explanation: >-
      The human classic phenotype lacks the haematologic and oncologic outcomes that dominate
      the mouse model.
notes: >-
  No GeneReviews chapter exists for RAD50-related Nijmegen breakage syndrome-like disorder;
  PubMed searches for "RAD50 GeneReviews" and "Nijmegen breakage syndrome-like GeneReviews"
  returned no results (checked 2026-07-31), so the usual GeneReviews phenotype baseline is
  unavailable and this entry is built directly from the primary case-report literature.
  PMID:20301355 IS a GeneReviews chapter, but it is the chapter for NBN-related Nijmegen
  breakage syndrome and is cited here only as the authoritative source for the differential
  diagnosis. It is deliberately NOT tagged GeneReviews in the references block, because
  that tag would wrongly imply RAD50-related NBSLD has a GeneReviews baseline.

  Additional Orphanet-listed features not yet curated here, because no verified
  primary-source snippet was found for them, include mild spasticity, slight
  non-progressive ataxia, hyperopia, multiple pigmented nevi, widely spaced nipples and
  clinodactyly. These are recoverable via the repo's ORPHA structured source
  (ORPHA:240760) once the Orphadata bulk XML is refreshed - references_cache/ORPHA_240760.md
  is not currently present in this checkout, and data/orphadata/ holds only the MANIFEST,
  so the rows could not be quoted. Regenerating that cache and adding the six features is a
  well-defined follow-up.

  Note on quotable scope: four of the cited references are cached as FULL TEXT
  (PMID:33378670 full_text_xml; PMID:41798197, PMID:40968163, PMID:40009290 full_text_pdf),
  and the reference validator matches against the cached body rather than the abstract, so
  full-text statements in those four are quotable. Phenotypes drawn from the PMID:33378670
  and PMID:41798197 full texts are curated accordingly. Features remaining uncurated are
  those reported only in sources NOT cached here - sensorineural hearing loss, Chiari
  malformation and the Wolff-Parkinson-White pattern, which the deep-research sweep
  attributes to reports outside this reference set.
references:
- reference: PMID:19409520
  title: Human RAD50 deficiency in a Nijmegen breakage syndrome-like disorder.
- reference: PMID:32212377
  title: "Human RAD50 deficiency: Confirmation of a distinctive phenotype."
- reference: PMID:33378670
  title: A Disease-Causing Single Amino Acid Deletion in the Coiled-Coil Domain of RAD50 Impairs MRE11 Complex Functions in Yeast and Humans.
- reference: PMID:37794136
  title: Bone Marrow Failure and Immunodeficiency Associated with Human RAD50 Variants.
- reference: PMID:41655867
  title: "Expanding the mutational spectrum of RAD50: a case report of Nijmegen breakage syndrome-like disorder in a Chinese child."
- reference: PMID:41798197
  title: Novel RAD50 variants lead to Nijmegen Breakage Syndrome-like disorder and unplanned recombinant human growth hormone treatment response.
- reference: PMID:41031707
  title: RAD50 missense variants differentially affect the DNA damage response and mitotic progression.
- reference: PMID:12208847
  title: Cancer predisposition and hematopoietic failure in Rad50(S/S) mice.
- reference: PMID:40968163
  title: Structural basis for DNA break sensing by human MRE11-RAD50-NBS1 and its regulation by telomeric factor TRF2.
- reference: PMID:40009290
  title: Population-based study of recurrent DNA damage response gene variants in breast cancer cases.
- reference: PMID:20301355
  title: Nijmegen Breakage Syndrome.

📚

References & Deep Research

References

11

PMID:19409520

Human RAD50 deficiency in a Nijmegen breakage syndrome-like disorder.

No top-level findings curated for this source.

PMID:32212377

Human RAD50 deficiency: Confirmation of a distinctive phenotype.

No top-level findings curated for this source.

PMID:33378670

A Disease-Causing Single Amino Acid Deletion in the Coiled-Coil Domain of RAD50 Impairs MRE11 Complex Functions in Yeast and Humans.

No top-level findings curated for this source.

PMID:37794136

Bone Marrow Failure and Immunodeficiency Associated with Human RAD50 Variants.

No top-level findings curated for this source.

PMID:41655867

Expanding the mutational spectrum of RAD50: a case report of Nijmegen breakage syndrome-like disorder in a Chinese child.

No top-level findings curated for this source.

PMID:41798197

Novel RAD50 variants lead to Nijmegen Breakage Syndrome-like disorder and unplanned recombinant human growth hormone treatment response.

No top-level findings curated for this source.

PMID:41031707

RAD50 missense variants differentially affect the DNA damage response and mitotic progression.

No top-level findings curated for this source.

PMID:12208847

Cancer predisposition and hematopoietic failure in Rad50(S/S) mice.

No top-level findings curated for this source.

PMID:40968163

Structural basis for DNA break sensing by human MRE11-RAD50-NBS1 and its regulation by telomeric factor TRF2.

No top-level findings curated for this source.

PMID:40009290

Population-based study of recurrent DNA damage response gene variants in breast cancer cases.

No top-level findings curated for this source.

PMID:20301355

Nijmegen Breakage Syndrome.

No top-level findings curated for this source.

Deep Research

2

Claude Code ▸

Nijmegen Breakage Syndrome-Like Disorder (RAD50 Deficiency): Comprehensive Research Report

claude-haiku-4-5-20251001, claude-sonnet-5 32 citations 2026-07-31T05:24:00.494440

Nijmegen Breakage Syndrome-Like Disorder (RAD50 Deficiency): Comprehensive Research Report

1. Disease Information

Overview. Nijmegen breakage syndrome-like disorder (NBSLD) is an ultra-rare autosomal recessive chromosomal-instability syndrome caused by biallelic pathogenic variants in RAD50, which encodes the structural ATPase core of the MRE11–RAD50–NBS1 (MRN) DNA double-strand-break (DSB) sensing/repair complex. It is the clinical and molecular "sibling" of classic Nijmegen breakage syndrome (NBS, caused by NBN mutations) and ataxia-telangiectasia-like disorder (ATLD, caused by MRE11A mutations) — together the three MRN-complex genetic diseases. NBSLD is defined by severe pre- and postnatal growth failure, congenital/progressive microcephaly, mild-to-borderline intellectual disability, radioresistant DNA synthesis, and spontaneous chromosomal instability, but characteristically lacks the severe combined immunodeficiency and high cancer predisposition that define classic NBS (OMIM: "Nijmegen breakage syndrome-like disorder; NBSLD" OMIM:613078). It is exceptionally rare: fewer than ten molecularly confirmed patients/families have been reported worldwide as of 2026 (Weemaes 1981 [clinical description predating molecular diagnosis]; Waltes et al. 2009 [PMID:19409520]; Chansel-Da Cruz et al. 2020; Ragamin et al. 2020 [PMID:32449290]; Takagi/Kanegane et al. 2023; a 2026 Chinese case; a 2026 Frontiers in Endocrinology growth-hormone case report).

Key identifiers: - OMIM: #613078 (disorder); *604040 (RAD50 gene) - Orphanet: ORPHA240760 (contrasted with classic NBS, ORPHA647) - MONDO: MONDO:0013118 - MedGen/UMLS concept: C2751318 (NCBI MedGen) - Gene: RAD50, HGNC:9816, NCBI Gene ID 10111, chromosome 5q31.1 - ICD-10/11: No dedicated code exists; typically coded under Q87.8 (other specified congenital malformation syndromes) or grouped with chromosome-instability syndromes - MeSH: Indexed under the broader "DNA Repair-Deficiency Disorders" / "Chromosome Breakage Syndromes" headings; no dedicated MeSH descriptor

Synonyms: NBS-like disorder; NBSLD; RAD50 deficiency; NBS2 (informal); "Nijmegen breakage syndrome 2" (non-standard, avoid confusion with NBS itself).

Evidence basis: All current knowledge derives from individual, molecularly confirmed case reports (n≈6–9 patients across ~6 publications) rather than aggregated registries or large cohort studies — a critical distinction from classic NBS, for which the Slavic-population founder mutation has generated a >130-patient international registry (Frontiers in Immunology, 2020, PMC7819964). Prevalence estimates for NBSLD are therefore extrapolated as "<1 in 1,000,000" by OMIM/Orphanet rather than measured directly.

2. Etiology

Disease causal factor: NBSLD is purely monogenic/Mendelian — biallelic (homozygous or compound heterozygous) loss-of-function or hypomorphic variants in RAD50 are necessary and sufficient to cause disease. There is no known environmental, infectious, or multifactorial contribution to primary disease causation.

Genetic risk factors: - Causal variants (biallelic, required): Reported alleles include: - A maternally inherited nonsense mutation + paternally inherited stop-codon readthrough mutation causing a 66-amino-acid C-terminal protein extension (Waltes et al. 2009, PMID:19409520) - Homozygous c.2524G>A (splice donor disruption at the final base of exon 15), producing a major transcript with exon 15 skipping → frameshift (p.Met800Phefs7) and a minor transcript with a missense change (p.Val842Ile) (Ragamin et al. 2020, PMC7318339) - RAD50 E1035Δ — an in-frame single-amino-acid deletion in the coiled-coil domain, acting as a "separation-of-function" allele (Chansel-Da Cruz et al. 2020, PMC7788285) - Compound heterozygous c.3806_3807del (p.His1269Argfs*2) + c.2531G>A (p.Ser844Asn), both classified VUS, in a 2026 Chinese case (ScienceDirect, S037811192600051X) - Two distinct compound-heterozygous variants in a patient with bone-marrow failure/immunodeficiency features (Takagi/Kanegane 2023, J Clin Immunol, DOI:10.1007/s10875-023-01591-8) - Zygosity: Both homozygous (typically in consanguineous families) and compound heterozygous configurations reported. - Modifier/susceptibility (distinct condition, not NBSLD): Monoallelic (heterozygous) RAD50 variants are instead studied as cancer-susceptibility alleles — e.g., RAD50 c.687delT is a low-penetrance breast-cancer risk allele in the Finnish population (PMC3006189), and RAD50 zinc-hook-domain LoF variants confer familial esophageal squamous cell carcinoma risk (PMC8472384). A 2024 systematic review/meta-analysis found no significantly increased breast cancer risk for most RAD50 heterozygous pathogenic variants overall (OR 0.93, 95% CI 0.74–1.16), with c.687del as a specific exception (onlinelibrary.wiley.com/doi/full/10.1002/ijc.35066). - Founder effects:* None established for RAD50-NBSLD (contrast with the well-characterized NBN c.657_661del5 Slavic founder mutation for classic NBS, carrier frequency 0.5–1%, PMC5148078/PMC7819964). Each NBSLD family reported to date carries private/novel variants.

Environmental risk factors: None identified as causal. Ionizing radiation is not a cause but is a major secondary hazard given cellular radiosensitivity (see Diagnostics/Prevention).

Protective factors: None specifically described for NBSLD. By analogy to RAD50 heterozygosity literature, monoallelic carriers are generally asymptomatic carriers, not protected individuals.

Gene-environment interactions: The defining cellular gene-environment interaction is radiosensitivity — RAD50-deficient cells fail to arrest DNA synthesis after ionizing radiation exposure ("radioresistant DNA synthesis," RDS) due to defective ATM-dependent checkpoint signaling, making diagnostic/therapeutic radiation exposure disproportionately genotoxic in these patients (multiple sources below).

3. Phenotypes

Phenotypes are drawn from the ~6 reported cases; frequencies below are counts observed across the small case series (not population-level percentages) and should be read as qualitative/case-count "frequency," per Orphanet and OMIM clinical synopsis language.

Phenotype	Type	Onset	Frequency in reported cases	Suggested HPO term
Severe prenatal growth retardation / IUGR	Physical/laboratory	Prenatal	~75% (3/4 in one series)	HP:0001511 (Intrauterine growth retardation)
Persistent postnatal growth restriction / short stature	Physical	Congenital–lifelong	~100%	HP:0008897 (Postnatal growth retardation); HP:0004322 (Short stature)
Congenital microcephaly, often progressive	Physical	Congenital, progressive	100%	HP:0000252 (Microcephaly); HP:0000253 (Progressive microcephaly)
Mild-to-borderline intellectual disability / learning difficulty	Cognitive	Childhood	Variable (borderline IQ ~85 in one patient; "no decline" reported)	HP:0006889 (Mild global developmental delay) / HP:0001256 (Intellectual disability, mild)
Craniofacial dysmorphism: sloping forehead, prominent eyes, broad nasal ridge, hypoplastic nasal septum, epicanthal folds, micrognathia, low-set rotated ears	Physical	Congenital	Common across cases	HP:0000340 (Sloping forehead); HP:0000520 (Proptosis); HP:0000431 (Wide nasal bridge); HP:0000286 (Epicanthus); HP:0000347 (Micrognathia); HP:0000369 (Low-set ears)
Spontaneous chromosomal instability (lymphocyte breakage/rearrangement)	Laboratory	—	Present in some patients, normal karyotype in others (variant-dependent)	HP:0040012 (Chromosomal instability)
Cellular hypersensitivity to ionizing radiation / radioresistant DNA synthesis	Laboratory	—	100% (defining feature)	HP:0032993 (Abnormal cellular DNA damage response, closest term) — no dedicated RDS HPO term exists
Sensorineural hearing loss (90 dB, bilateral)	Physical/laboratory	Diagnosed age 2 in one patient	1 reported case	HP:0000407 (Sensorineural hearing loss)
Speech and motor delay	Developmental	Infancy	Reported in multiple cases	HP:0000750 (Delayed speech and language development); HP:0001270 (Motor delay)
Chiari malformation (cerebellar tonsillar herniation)	Physical/imaging	—	1 reported case	HP:0007099 (Chiari type I malformation)
Wolff-Parkinson-White pattern (without arrhythmia)	Cardiac	—	1 reported case	HP:0011712 (Ventricular pre-excitation)
Bilateral clinodactyly / brachydactyly with sandal gap	Skeletal	Congenital	Multiple cases	HP:0030084 (Clinodactyly); HP:0001156 (Brachydactyly)
Multiple café-au-lait macules	Skin	—	Multiple cases	HP:0000957 (Café-au-lait spot)
Mild spasticity; slight, nonprogressive ataxia	Neurological	—	Reported (Orphanet)	HP:0001257 (Spasticity); HP:0001251 (Ataxia — nonprogressive, distinguishing from ATLD)
Hyperopia	Ocular	—	Reported (Orphanet)	HP:0000540 (Hyperopia)
Widely spaced nipples	Physical	Congenital	Reported (Orphanet)	HP:0006610 (Wide intermamillary distance)
Normal sexual development / no hormonal deficiency	—	—	Consistent across all cases	Absence of HP:0000811 (Hypogonadism)
Absent severe/recurrent infections, immunodeficiency, myelodysplasia, or early neurodegeneration	—	—	Defining negative finding distinguishing NBSLD from NBS/ATLD	—
Bone marrow failure (thrombocytopenia, anemia, neutropenia, aplastic anemia) + B-lymphocyte deficiency	Laboratory/hematologic	Variable, one case age 7	Reported in a phenotypic-spectrum-expanding subset (Chansel-Da Cruz 2020; Takagi 2023) — contradicts the "no immunodeficiency" rule for certain hypomorphic/separation-of-function alleles	HP:0005528 (Bone marrow hypocellularity); HP:0004313 (Decreased circulating antibody level); HP:0002846 (Abnormal B cell count)
Early-onset cataract (age 10)	Ocular	Childhood	1 case (Chansel-Da Cruz)	HP:0000518 (Cataract)
Bilateral cryptorchidism, distinctive craniofacial features (Chinese case)	Physical	Congenital	1 case	HP:0000028 (Cryptorchidism)

Quality-of-life impact: No formal QoL instrument (EQ-5D/SF-36) data exist for this ultra-rare disease. Reported functional impact centers on growth failure requiring endocrine evaluation, hearing loss requiring amplification, and developmental/learning support; notably, unlike classic NBS, no reported neurodegeneration or decline in intellectual/motor function over time in the two best-characterized patients ("no decline of intellectual or motor functions has been observed").

4. Genetic/Molecular Information

Causal gene: RAD50 (RAD50 double-strand break repair protein), OMIM *604040, HGNC:9816, chr 5q31.1, NCBI Gene 10111.

Gene/protein function: RAD50 is a structural-maintenance-of-chromosomes (SMC)-family ATPase that, together with MRE11 and NBS1, forms the MRN complex — among the earliest sensors of DNA double-strand breaks. RAD50 uses its ABC-type ATPase domain, a Zn-hook dimerization motif, and long antiparallel coiled-coils to bridge broken DNA ends, gate MRE11 nuclease access for 5′→3′ end resection, tether sister chromatids, and license ATM kinase activation for checkpoint signaling (PMC4494100; GeneCards RAD50).

Pathogenic variant classes reported in NBSLD: - Nonsense/truncating: classic LoF, near-complete loss of protein - Stop-codon readthrough (extension) mutations: abnormal C-terminal extension impairing folding/stability - Splice-site disruption: e.g., c.2524G>A causing exon-15 skipping/frameshift, with a minor missense-producing transcript as a partial "leaky" allele - In-frame single-residue deletion (separation-of-function): RAD50 E1035Δ in the coiled-coil domain — selectively impairs DNA end resection/HR/replication-fork function while sparing ATM-dependent checkpoint signaling, illustrating that NBSLD's clinical spectrum can fractionate along distinct MRN sub-functions (PMC7788285) - Compound heterozygous frameshift + missense (VUS): e.g., c.3806_3807del + c.2531G>A in the 2026 Chinese case, with the frameshift allele shown by Western blot to destabilize RAD50 protein

Variant classification: Most reported variants are classified pathogenic/likely pathogenic per ACMG/AMP given segregation, protein-loss functional data, and de novo absence in gnomAD; two recent Chinese-case variants remain formally VUS pending further functional confirmation.

Allele frequency: RAD50 loss-of-function alleles are individually ultra-rare in population databases — e.g., the Ragamin et al. splice variant had a minor allele frequency of only 1.072×10⁻⁴ in gnomAD, observed only in heterozygous state (consistent with a rare, non-founder recessive allele).

Somatic vs. germline: All NBSLD-causing variants are constitutional/germline. (Somatic RAD50 alterations are separately studied in sporadic cancers via COSMIC/TCGA but are not part of this Mendelian disease.)

Functional consequences at the protein/cellular level: - Near-undetectable RAD50 protein by Western blot in patient fibroblasts, with secondary reduction of MRE11 and NBS1 protein levels (complex destabilization) — "RAD50 protein was almost undetectable in the F583 fibroblasts," with a "more pronounced reduction than previously reported" in the first patient (PMC7318339) - Failure of DNA-damage-induced MRN nuclear focus formation - Impaired ATM autophosphorylation and downstream substrate phosphorylation (CHK2 pSer19, KAP1/TRIM28 pSer824) after irradiation — "barely detectable at 6 Gy" - Radioresistant DNA synthesis (failure of the intra-S-phase checkpoint) mimicking ataxia-telangiectasia cells - Chromosomal instability in metaphase spreads (variable — one patient had a normal karyotype despite RDS, showing phenotypic/cytogenetic dissociation across alleles)

Modifier genes: None specifically established for NBSLD; by extension from MRN biology, TP53/ATM pathway status could theoretically modulate cellular phenotype but this is not documented in patients.

Epigenetic information: No disease-specific DNA methylation/chromatin studies have been published for RAD50-NBSLD specifically (contrast with broader MRN-complex chromatin-remodeling literature, PMID:17713585).

Chromosomal abnormalities: NBSLD is not a copy-number/structural chromosomal disorder — it is a sequence-level Mendelian gene defect that secondarily produces acquired chromosomal instability (translocations, breaks) as a cellular biomarker, not a germline CNV.

5. Environmental Information

Environmental factors: Not causal, but critically relevant to iatrogenic risk: diagnostic/therapeutic ionizing radiation (X-ray, CT) poses disproportionate genotoxic/carcinogenic risk in RAD50-deficient patients due to radiosensitivity and impaired DSB repair; MRI and ultrasound are preferred alternatives (per management recommendations extrapolated from NBS and stated explicitly by Ragamin et al. 2020).
Lifestyle factors: No specific lifestyle risk-modifying data published (disease is congenital/genetic, onset neonatal).
Infectious agents: Not implicated in causation. Because immunodeficiency is largely (though not universally) absent in NBSLD — unlike classic NBS — recurrent infection susceptibility is not a defining environmental interaction, except in the minority of reported patients with bone-marrow failure/immunologic involvement (Takagi 2023; Chansel-Da Cruz 2020), where infection risk parallels that of primary immunodeficiency generally.

6. Mechanism / Pathophysiology

Causal chain (trigger → clinical manifestation):

Molecular trigger: Biallelic RAD50 variants → loss/destabilization of RAD50 protein → destabilization of the entire MRN (MRE11-RAD50-NBS1) complex (secondary reduction of MRE11 and NBS1 protein even though those genes are wild-type).
Cellular DSB-sensing failure: Loss of MRN focus formation at DNA double-strand breaks → failure to recruit and activate ATM kinase → loss of ATM-dependent phosphorylation cascade (CHK2, KAP1/TRIM28, and other substrates) → failure of the intra-S-phase checkpoint, manifesting as radioresistant DNA synthesis.
Genome instability: Impaired DSB end-resection (MRE11 nuclease access gated by RAD50 ATPase cycling) → defective homologous recombination repair → spontaneous and radiation-induced chromosomal instability (breaks, rearrangements) in some alleles; separation-of-function alleles (e.g., E1035Δ) show this resection/HR defect can be dissociated from the ATM-signaling defect, since ATM signaling and G2/M checkpoint remained intact in that patient despite defective resection.
Developmental consequence: Chronic replication stress and genome instability during embryonic/fetal neurodevelopment and somatic growth are hypothesized (by analogy to NBS/ATLD/microcephaly-primary genes) to drive severe growth failure and progressive microcephaly, likely reflecting impaired proliferation and increased apoptosis of neural progenitor and other rapidly dividing cell pools — the same final-common mechanism invoked broadly for "microcephaly-DNA repair" disorders.
Divergence from NBS/ATLD: Because RAD50 hypomorphic alleles in reported patients retain partial complex function (unlike complete NBS1 or MRE11 loss), the downstream immune and oncogenic consequences are attenuated in most patients — plausibly because sufficient residual MRN activity supports V(D)J recombination/class-switch recombination and tumor-suppressive checkpoint function, while growth/neurodevelopmental pathways (more sensitive to replication stress) are still impaired. This is a hypothesis, not established by direct mechanistic study, and the emerging bone-marrow-failure phenotype in some patients (Takagi 2023, Chansel-Da Cruz 2020) shows this attenuation is allele-dependent and incomplete.

Molecular pathways: DNA damage response (DDR) / ATM-CHK2 checkpoint signaling pathway (KEGG hsa03450 Non-homologous end-joining; hsa03440 Homologous recombination; Reactome "DNA Double-Strand Break Repair").

Cellular processes (GO terms): - GO:0006302 double-strand break repair - GO:0000724 double-strand break repair via homologous recombination - GO:0007049 cell cycle / GO:0000077 DNA damage checkpoint signaling - GO:0006281 DNA repair - GO:0004725 (not applicable here; relevant to other modules) — instead: GO:0005524 ATP binding (RAD50 ATPase activity)

Protein dysfunction: Predominantly loss of function via destabilization/truncation; one well-characterized allele (E1035Δ) demonstrates a separation-of-function mechanism — selective loss of DNA-end-resection/replication-fork functions with preserved ATM-signaling function, attributed to disruption of coiled-coil heptad-repeat conformational dynamics (PMC7788285).

Metabolic changes: Not specifically documented for NBSLD.

Immune system involvement: Variable and allele-dependent — absent in "classic" NBSLD (Waltes 2009, Ragamin 2020), but documented in an emerging subset with bone marrow failure, B-lymphocyte deficiency, and impaired T-lymphopoiesis (Chansel-Da Cruz 2020: "virtual absence of B lymphocytes; impaired T lymphopoiesis"; Takagi 2023 patient with immunodeficiency).

Tissue damage mechanisms: Genome instability/replication stress in high-turnover progenitor pools (neural, hematopoietic, germline) rather than classical oxidative/ischemic/fibrotic injury.

Biochemical abnormalities: Defective RAD50 ATPase/Zn-hook function; failure of ATM autophosphorylation (Ser1981) and substrate phosphorylation after ionizing radiation.

Suggested cell types (CL terms) and biological processes (GO terms) for pathophysiology nodes: - CL:0000034 stem cell / CL:0000037 hematopoietic stem cell (bone-marrow-failure subset) - CL:0000542 lymphocyte / CL:0000236 B cell / CL:0000084 T cell (immunodeficiency subset) - CL:0011020 neural progenitor cell (microcephaly mechanism, by analogy) - GO:0000724 double-strand break repair via homologous recombination - GO:0031573 intra-S DNA damage checkpoint signaling - GO:0006974 DNA damage response

Molecular profiling / advanced technologies: No transcriptomic, proteomic, metabolomic, single-cell, or spatial-omics datasets specific to human NBSLD patient tissue have been published (GEO/ArrayExpress search did not return disease-specific datasets); available molecular data are limited to targeted Western blot, immunofluorescence (MRN foci), and functional cellular assays (RDS, chromosome breakage, ATM-substrate phosphoblotting) in patient-derived fibroblasts/lymphoblasts.

7. Anatomical Structures Affected

Organ level: - Primary: Craniofacial skeleton/brain (microcephaly, dysmorphic facies), skeletal system (growth plates — short stature, brachydactyly/clinodactyly), skin (café-au-lait macules) - Secondary: Inner ear (sensorineural hearing loss), cardiac conduction system (WPW pattern in one case), cerebellum/craniocervical junction (Chiari malformation), ocular (hyperopia, cataract in one allele), hematopoietic system and immune organs (bone marrow, lymphoid tissue — in the emerging severe subset), testes (cryptorchidism in one case) - Body systems: Musculoskeletal, nervous, integumentary, and — in a subset — hematologic/immune systems

Tissue and cell level: - Neural progenitor cells and developing cerebral cortex (microcephaly) - Growth-plate chondrocytes/osteoblasts (short stature, skeletal dysmorphism) - Cochlear hair cells / auditory neuroepithelium (sensorineural hearing loss) - Hematopoietic stem/progenitor cells, B and T lymphocytes (bone marrow failure subset) - Fibroblasts (the primary experimental cell type used for all functional/cellular studies — radiosensitivity, MRN foci, RDS assays)

Subcellular level (GO Cellular Component): - GO:0005634 nucleus (site of MRN complex action) - GO:0000784 nuclear chromosome, telomeric region (MRN telomere maintenance role) - GO:0035861 site of double-strand break

Localization (UBERON): - UBERON:0000955 brain; UBERON:0001851 cortex - UBERON:0001690 ear / UBERON:0001846 cochlea - UBERON:0002371 bone marrow - UBERON:0002370 thymus (T-lymphopoiesis) - UBERON:0000178 blood - Bilateral/symmetric involvement typical (microcephaly, growth failure); no lateralization reported.

8. Temporal Development

Onset: Congenital/prenatal onset — severe intrauterine growth restriction and microcephaly are present from birth; postnatal growth restriction and microcephaly (often progressive) continue through childhood. This places NBSLD onset squarely in the neonatal/congenital category (OMIM lists "age of onset in the neonatal period").

Progression: - Growth/head circumference: Progressive postnatal microcephaly documented in longitudinal case follow-up (e.g., patient followed to age 15 showed head circumference declining further below population norms). - Neurocognitive: Notably stable, non-progressive course in the best-documented patients — "no decline of intellectual or motor functions has been observed," and ataxia (when present) is described as "slight and nonprogressive," a key distinguishing feature from the progressive cerebellar degeneration of ATLD. - Hematologic/immune (severe subset): Progressive bone marrow failure has been documented in at least one patient, evolving over time (age 7 onward) to aplastic anemia — a distinct and more severe disease trajectory. - Disease course pattern: Predominantly stable/static dysmorphic-growth phenotype punctuated by an occasional progressive hematologic/immunologic trajectory in a minority of alleles. - Duration: Chronic, lifelong condition; the oldest reported patient was followed to at least 23 years of age (Waltes et al. 2009) without malignancy.

Patterns: - No spontaneous remission described (structural/growth features are static; hematologic decline in the severe subset does not remit spontaneously). - Critical periods: Prenatal and early postnatal periods are the critical windows for growth/head-circumference deficits, given congenital onset; genetic evaluation prior to any elective growth-hormone therapy is now explicitly recommended as a "critical intervention window" issue, since GH was started empirically (without genetic workup) in the 2026 Chinese case before RAD50 deficiency was recognized.

9. Inheritance and Population

Epidemiology: Prevalence <1 per 1,000,000 (OMIM/Orphanet estimate); incidence not separately calculable given fewer than 10 total published patients. This contrasts sharply with classic NBS, whose Slavic founder mutation gives regional prevalence up to >20 per 1,000,000 in parts of Belarus/Ukraine (PMC7819964).

Inheritance pattern: Autosomal recessive (AR); all reported cases are homozygous or compound heterozygous for biallelic RAD50 variants.

Penetrance: Presumed complete for the core growth/microcephaly phenotype in biallelic carriers (all reported patients manifest disease); however, phenotypic severity varies considerably by allele (from mild "classic" NBSLD to severe bone-marrow-failure phenotypes), suggesting variable expressivity driven largely by hypomorphic vs. separation-of-function vs. near-null allele combinations rather than incomplete penetrance per se.

Genetic anticipation: Not described/applicable (not a repeat-expansion disorder).

Germline mosaicism: Not specifically reported for RAD50-NBSLD.

Founder effects: None established (contrast NBN c.657del5 Slavic founder mutation, carrier frequency 0.5–1%, PMC5148078). Each RAD50-NBSLD family reported carries private variants; the disorder has been documented in Turkish (consanguineous), European, and Chinese families, arguing against a single founder population.

Consanguinity: A major risk factor in reported cases — e.g., the second reported patient (Ragamin et al. 2020) was homozygous for a novel variant, born to consanguineous Turkish parents.

Carrier frequency: Not established at a population level (each variant is individually ultra-rare; gnomAD MAF ~1.07×10⁻⁴ heterozygous-only for one reported allele).

Population demographics: Reported patients span European (Dutch/German, original 2009 report), Turkish, and Chinese ancestries — no clear ethnic clustering, unlike NBS's strong Slavic association.

Geographic distribution: No endemic region identified; cases are geographically scattered case reports (Netherlands/Germany, Turkey, China, Japan [Takagi/Kanegane group]).

Sex ratio: Both male and female patients reported (e.g., 23-year-old female in Waltes 2009; 15-year-old female in Ragamin 2020; male patients in the Chinese/GH case reports) — no established sex predilection given small numbers.

Age distribution: Diagnoses reported from infancy through the mid-20s in the oldest documented patient; disease is lifelong from a congenital onset.

10. Diagnostics

Clinical laboratory tests: - Radioresistant DNA synthesis (RDS) assay — the key functional diagnostic test, measuring failure of DNA synthesis suppression after ionizing radiation exposure in patient fibroblasts/lymphocytes; abnormal (elevated) RDS is shared with ataxia-telangiectasia, NBS, and ATLD, so it is not RAD50-specific by itself. - Chromosomal breakage/instability analysis (metaphase cytogenetics) — variably abnormal. - Clonogenic radiosensitivity assay (colony survival after ionizing radiation) — demonstrates hypersensitivity. - Western blot for RAD50/MRE11/NBS1 protein levels in patient-derived fibroblasts — shows absent/reduced RAD50 with secondary reduction of complex partners; this is the most disease-specific functional readout. - Immunofluorescence for MRN nuclear foci after DNA damage — shows failure of focus formation. - ATM-pathway phosphoprotein assays — absent/reduced phospho-CHK2 (Ser19), phospho-KAP1/TRIM28 (Ser824) post-irradiation.

Biomarkers: No circulating serum/plasma biomarker exists; diagnosis relies on cellular functional assays plus molecular genetics. (For context, classic NBS diagnostic workup also includes serum immunoglobulin levels and lymphocyte subsets — largely normal in NBSLD, distinguishing it.)

Imaging: Brain MRI recommended over CT (radiosensitivity) — has shown Chiari malformation in at least one patient; skeletal survey for growth/skeletal dysmorphism; ionizing-radiation imaging (X-ray, CT) should be minimized given cellular radiosensitivity.

Functional/electrophysiology tests: Audiometry (identified 90 dB bilateral sensorineural hearing loss in one patient); ECG (identified WPW pattern in one patient, without arrhythmia).

Biopsy/histopathology: Not a standard diagnostic requirement; disease diagnosis relies on fibroblast functional assays rather than tissue biopsy/histopathology.

Genetic testing: - Recommended approach: Given phenotypic overlap with NBS/ATLD/other microcephaly-DNA-repair disorders, a multi-gene panel covering RAD50, NBN, MRE11A, ATM, and related chromosomal-instability genes is the recommended first-line approach, escalating to whole-exome sequencing (WES) — which is how essentially all reported NBSLD cases have actually been solved (trio-based WES in the recent Chinese case; WES in the Takagi 2023 case). - Single-gene RAD50 sequence analysis (all coding exons) is commercially available (NCBI GTR test ID 578298, ncbi.nlm.nih.gov/gtr/tests/578298). - Chromosomal microarray/karyotype/FISH: Not primary diagnostic tools (NBSLD is a sequence-level, not copy-number, disorder), though karyotype may show acquired instability. - Whole genome sequencing (WGS): Not specifically reported as used but would capture splice-region variants like c.2524G>A that WES might miss without careful splice analysis. - Functional RNA studies (RT-PCR): Essential for confirming splice-site variant pathogenicity (as done for c.2524G>A, revealing exon-15-skipping and missense transcripts).

Clinical diagnostic criteria: No formal consensus diagnostic criteria society guideline exists (disease is too rare); working diagnosis is based on the combination of (1) severe pre/postnatal growth failure + microcephaly, (2) laboratory evidence of radiosensitivity/RDS, and (3) biallelic RAD50 variants, with exclusion of the immunodeficiency/cancer features that would instead suggest classic NBS or a more severe RAD50-null/bone-marrow-failure phenotype.

Differential diagnosis: - Classic Nijmegen breakage syndrome (NBN mutations) — distinguished by severe combined immunodeficiency and high lymphoid malignancy risk - Ataxia-telangiectasia-like disorder (MRE11A mutations) — distinguished by progressive cerebellar ataxia/neurodegeneration, typically without microcephaly - Ataxia-telangiectasia (ATM mutations) - Other primary microcephaly syndromes (MCPH genes) - Seckel syndrome and other growth-failure/microcephaly syndromes - Fanconi anemia and other bone-marrow-failure syndromes (relevant differential for the severe subset with cytopenias)

Screening: No newborn screening program exists (disease too rare, no biochemical marker). Prenatal diagnosis/carrier screening is feasible via targeted molecular testing once a familial variant is known (as for any AR Mendelian disease), particularly relevant given documented consanguinity in some families.

11. Outcome / Prognosis

Survival/mortality: No formal survival statistics exist given the tiny cohort. The oldest well-documented patient survived to at least 23 years without malignancy (Waltes et al. 2009); a second patient was followed to 15 years without malignancy (Ragamin et al. 2020). This suggests a substantially better long-term prognosis than classic NBS, where malignancy (chiefly B-cell lymphoma) is the dominant cause of premature mortality, with lymphoid cancer developing in a large proportion of NBS patients by young adulthood.

Morbidity/function: Growth failure (short stature), microcephaly, and mild learning difficulties are the chronic morbidities; hearing loss and skeletal anomalies add functional burden in some patients. Critically, no progressive neurological decline has been documented in the core NBSLD phenotype (contrasting with ATLD's progressive ataxia and NBS's neurodevelopmental concerns).

Disease course/complications: - Core NBSLD: stable, non-progressive intellectual/motor course; growth and craniofacial features are static congenital findings. - Severe subset: progressive bone marrow failure (aplastic anemia), recurrent infection risk from B/T lymphopenia, early cataract — a materially worse prognosis paralleling inherited bone-marrow-failure syndromes. - Unknown/theoretical malignancy risk: because RAD50 is a DNA-repair/tumor-suppressor-pathway gene and its paralogs (NBN, MRE11A) confer cancer predisposition, authors explicitly recommend managing NBSLD patients with NBS-level cancer surveillance vigilance despite the absence of confirmed malignancy in the literature to date — an important prognosis caveat: absence of evidence for cancer risk (small n, sometimes short follow-up) is not evidence of absence.

Prognostic factors: Allele type appears to be the dominant driver of prognosis — near-null/complex-destabilizing alleles associate with the "classic" milder NBSLD phenotype in some patients, whereas certain alleles (e.g., RAD50 E1035Δ separation-of-function, or the compound heterozygous genotype in the Takagi 2023 patient) associate with a bone-marrow-failure/immunodeficiency trajectory — suggesting genotype-phenotype correlation exists but is not yet fully mapped across the small number of known alleles.

Prognostic biomarkers: None validated; residual RAD50/MRE11/NBS1 protein level and degree of ATM-signaling preservation are plausible (but unvalidated) prognostic correlates based on the mechanistic literature.

12. Treatment

There is no disease-specific or curative therapy for RAD50-NBSLD; management is supportive and extrapolated largely from classic NBS protocols, adjusted for the (usually) milder immune phenotype.

Pharmacotherapy: - No approved pharmacotherapy targets the RAD50/MRN defect itself. - Recombinant human growth hormone (rhGH) has been used off-label for short stature — a 2026 case report (Frontiers in Endocrinology) documented 5 years 9 months of rhGH (0.15–0.2 IU/kg/day, IGF-1-titrated) in a RAD50-NBSLD patient, improving height from −3.35 SD to −1.28 SD (average 7.3 cm/year growth velocity) with no adverse reactions observed and no tumor evidence at 5-year post-discontinuation follow-up. However, the authors explicitly flag this as an "unplanned" treatment response (GH was started before genetic diagnosis) and caution that genetic evaluation should precede GH therapy in syndromic short stature given the theoretical malignancy risk associated with impaired DNA-repair capacity — a risk-benefit issue specific to DNA-repair-deficiency syndromes (GH/IGF-1 signaling is mitogenic). - IVIG replacement and prophylactic antibiotics — used empirically in the immunodeficient/bone-marrow-failure subset, extrapolated from NBS management (not specifically trialed in NBSLD but standard for the phenotypic overlap group).

Advanced therapeutics: - Hematopoietic stem cell transplantation (HSCT) — not reported specifically for RAD50-NBSLD in the literature reviewed, but would be the standard consideration for the bone-marrow-failure subset (by analogy to other inherited BMF syndromes and to NBS management for severe immunodeficiency), with the caveat that conditioning-regimen radiosensitivity would require radiation- and alkylator-reduced conditioning protocols, again by analogy to ATM/MRN-pathway-deficient HSCT literature. - Gene therapy, cell therapy (beyond HSCT), RNA-based therapies, and targeted molecular therapies have not been reported for this disorder.

Surgical/interventional: No disease-specific surgical intervention; management of individual complications (e.g., cataract extraction, Chiari decompression if symptomatic) would follow standard surgical practice, with radiologic planning shifted toward non-ionizing modalities where feasible.

Supportive/rehabilitative care: - Speech/motor developmental therapy (physical therapy, occupational therapy, speech therapy) for developmental delay - Hearing aids/audiologic support for sensorineural hearing loss - Nutritional support for growth failure - Multidisciplinary genetics, endocrinology, hematology/immunology, and neurology follow-up

Experimental treatments: No registered clinical trials specific to RAD50-NBSLD were identified in this search (ClinicalTrials.gov has no RAD50-NBSLD-specific studies; broader NBS-related trials focus on classic NBN-mutated NBS, e.g., cancer surveillance and antioxidant studies).

Treatment outcomes/adverse events: The only quantified treatment-outcome data available are from the rhGH case (above) — no other systematic treatment-response data exist.

Treatment strategy / algorithm (extrapolated from NBS + expert case-report recommendations): 1. Confirm molecular diagnosis (WES/panel) before initiating any growth-promoting or immunomodulatory therapy. 2. Avoid ionizing-radiation-based imaging; prefer MRI/ultrasound. 3. Baseline and periodic assessment of growth, immune function (immunoglobulins, lymphocyte subsets), cognitive development, and hematologic parameters (given emerging BMF phenotype). 4. Consider rhGH for growth failure only after genetic counseling on theoretical cancer-risk trade-offs. 5. Empiric cancer surveillance (physical exam, blood counts, imaging as tolerated) analogous to NBS protocols, pending disease-specific evidence. 6. Avoid live vaccines if any immunodeficiency is confirmed (extrapolated from NBS guidance).

Suggested MAXO terms: - MAXO:0000647 chemotherapy — not applicable (no current chemo indication) - MAXO:0010039 organ/hematopoietic transplantation — for HSCT in BMF subset - MAXO:0000011 physical therapy; MAXO:0000930 speech therapy; MAXO:0001351 occupational therapy — for developmental support - MAXO:0000950 supportive care - Pharmacotherapy: NCIT:C15986 (generic) with therapeutic_agent bound to CHEBI/NCIT term for somatropin (recombinant human growth hormone)

13. Prevention

Primary prevention: Not applicable in the traditional sense (Mendelian genetic disease); the only "primary prevention" lever is genetic/reproductive counseling for known carrier couples (especially consanguineous families) to inform reproductive decision-making, and preimplantation genetic diagnosis (PGD) or prenatal testing once a familial pathogenic variant is identified.

Secondary prevention (early detection): Early molecular diagnosis via WES/panel testing in any infant presenting with severe pre/postnatal growth restriction plus congenital microcephaly (particularly without the severe immunodeficiency/infection pattern that would suggest classic NBS) allows earlier initiation of radiation-avoidance precautions and surveillance.

Tertiary prevention: Avoidance of ionizing radiation exposure (diagnostic and therapeutic) is the single most actionable, disease-specific preventive measure, given documented cellular radiosensitivity — this is analogous to, but with less certain magnitude of risk than, the well-established radiation-avoidance guidance for classic NBS and ataxia-telangiectasia.

Immunization: No NBSLD-specific vaccine guidance published; for the subset with confirmed immunodeficiency, standard primary-immunodeficiency vaccine precautions (avoidance of live vaccines pending immune assessment) would apply by extrapolation from NBS/PID management, not from disease-specific trial data.

Screening/genetic counseling: Carrier screening and cascade testing in relatives of an index case; genetic counseling emphasizing autosomal recessive inheritance (25% recurrence risk per pregnancy for carrier couples) and — as newly flagged by the 2026 GH case report — counseling before elective growth-promoting therapy given the theoretical mitogenic/malignancy-risk interaction with underlying DNA-repair deficiency.

Behavioral interventions / public health / prophylaxis: Not applicable beyond the radiation-avoidance and infection-precaution measures already described; this is not a disease with population-level environmental or infectious prevention levers.

14. Other Species / Natural Disease

Taxonomy: RAD50 is deeply evolutionarily conserved from yeast to human (NCBITaxon:9606 Homo sapiens for the human disease; orthologs exist across essentially all eukaryotes given the ancient, essential nature of DSB repair).

Naturally occurring disease in other species: No naturally occurring veterinary RAD50-deficiency syndrome analogous to human NBSLD has been reported in companion animals or wildlife (OMIA search did not surface a RAD50-associated natural veterinary disease); this contrasts with many other Mendelian disease genes that do have recognized veterinary/naturally-occurring counterparts.

Comparative biology / orthologous genes: - Mouse: Rad50 (MGI:109292) - Yeast: RAD50 (the original gene discovery organism — S. cerevisiae radiation-sensitive mutant screens) - Medaka fish: rad50 (used for an engineered disease model, see below) - Drosophila: Mre11-Rad50-Nbs ortholog complex (implicated in telomere capping during embryogenesis, PMID:19520832)

Transmission: Not applicable (non-infectious, non-zoonotic genetic disease).

15. Model Organisms

Genetic models: - Mouse complete Rad50 knockout: Embryonic lethal — a null Rad50 mutation, which presumably fully abrogates the structural role of the Mre11 complex, results in early embryonic death, underscoring RAD50's essential role in genome maintenance and precluding a viable full-knockout model of human disease. - Rad50^S/S hypomorphic mice (the disease-relevant model): a separation-of-function allele preserving MRN complex integrity but reducing function. Phenotype: partial embryonic lethality; shortened lifespan; progressive loss of germline and hematopoietic cells; death from hematopoietic failure by ~3 months of age; growth defects; cancer predisposition; cultured cells show increased spontaneous apoptosis and chromosomal instability; telomere-maintenance defects due to loss of MRN integrity (PMID:12208847, genesdev.cshlp.org/content/16/17/2237). This model recapitulates the cancer-predisposition and bone-marrow-failure arm of the human phenotypic spectrum (i.e., the severe subset) better than the "classic" milder human NBSLD presentation, illustrating that mouse hypomorphic models may better model the severe end of the human allelic spectrum. - Medaka fish CRISPR/Cas9 rad50 2-bp-deletion model (PLOS ONE 2023, PMC10129005): heterozygous rad50Δ2/+ medaka developed tumors in 8/10 fish and had reduced median survival (54.2 ± 2.6 weeks vs. 65.7 ± 1.1 weeks in controls); homozygous rad50Δ2/Δ2 fish were semi-lethal and reproduced most major ataxia-telangiectasia phenotypic features including ataxia — providing a tractable, transparent vertebrate model for both the cancer-predisposition and neurological aspects of MRN-complex disease, though notably modeling an AT-like rather than a growth-failure/microcephaly phenotype.

Model characteristics — recapitulation vs. limitations: - Both the mouse Rad50S/S and medaka rad50 models capture the cancer predisposition and hematopoietic/genome-instability dimensions of RAD50 dysfunction robustly. - Neither model fully recapitulates the core "classic" human NBSLD phenotype (severe growth restriction, progressive but non-degenerative microcephaly, absence of cancer/immunodeficiency) — a human-model mismatch: the animal models instead better represent the more severe bone-marrow-failure/malignancy-prone end of the human allelic spectrum, or an AT-like neurological phenotype, rather than the mild "classic" NBSLD growth/craniofacial phenotype first described by Waltes et al. This gap is consistent with the broader observation that complete or near-complete RAD50 loss is poorly tolerated in mammals (embryonic lethal), so viable human patients necessarily carry partial-function hypomorphic alleles whose precise residual activity is difficult to reproduce precisely in animal knock-in models. - Applications: These models remain valuable for studying MRN-complex-dependent tumor suppression, hematopoietic stem cell maintenance, ATM-pathway biology, and telomere maintenance mechanisms relevant to the RAD50-disease spectrum broadly.

Cellular/in vitro models: Patient-derived primary fibroblasts (the dominant experimental system in every published human case report) are used for radiosensitivity, RDS, chromosome-breakage, MRN-focus, and ATM-substrate-phosphorylation assays; no iPSC-derived model of RAD50-NBSLD has been reported.

Resources: MGI (mouse, Rad50 MGI:109292); no dedicated RAD50-NBSLD registry exists in ZFIN/FlyBase/WormBase; IMPC/KOMP conditional-knockout resources for Rad50 exist for research use given the lethality of full constitutive knockout.

Summary Table of Key Ontology Term Suggestions

Category	Terms
Disease	MONDO:0013118; OMIM:613078; ORPHA:240760
Gene	HGNC:9816 (RAD50); OMIM:604040
Key phenotypes	HP:0000252 (Microcephaly), HP:0001511 (IUGR), HP:0008897 (Postnatal growth retardation), HP:0040012 (Chromosomal instability), HP:0000407 (SNHL), HP:0001156 (Brachydactyly), HP:0030084 (Clinodactyly), HP:0000957 (Café-au-lait spot), HP:0001251 (Ataxia, nonprogressive), HP:0007099 (Chiari malformation), HP:0005528 (Bone marrow hypocellularity — severe subset)
Cell types	CL:0000057 fibroblast (primary experimental cell); CL:0000037 hematopoietic stem cell; CL:0000236 B cell; CL:0000084 T cell
Biological processes	GO:0000724 (DSB repair via HR), GO:0006974 (DNA damage response), GO:0031573 (intra-S DNA damage checkpoint)
Treatment	MAXO:0010039 (transplantation, BMF subset); NCIT:C15986 (Pharmacotherapy) + therapeutic_agent for somatropin/rhGH

Sources

OpenScientist ▸

Nijmegen Breakage Syndrome-like Disorder (NBSLD / RAD50 Deficiency): A Comprehensive Disease Characteristics Report

openscientist-autonomous 11 citations 2026-07-31T05:42:21.545889

Nijmegen Breakage Syndrome-like Disorder (NBSLD / RAD50 Deficiency): A Comprehensive Disease Characteristics Report

Disease category: Mendelian (autosomal recessive) · Gene: RAD50 · OMIM #613078 · MONDO:0013415 · Orphanet: NBS-like spectrum

Summary

Nijmegen breakage syndrome-like disorder (NBSLD) is an ultra-rare, autosomal-recessive chromosomal-instability syndrome caused by biallelic loss-of-function or hypomorphic variants in RAD50, the gene encoding a core structural ATPase subunit of the MRE11–RAD50–NBS1 (MRN) complex. The MRN complex is the primary cellular sensor of DNA double-strand breaks (DSBs); it recruits and activates the ATM kinase, initiating the DNA damage response (DDR). When RAD50 protein is absent or destabilized, cells cannot assemble DNA-damage-induced MRN foci, fail to activate ATM properly, lose cell-cycle checkpoint control, exhibit radioresistant DNA synthesis, and accumulate chromosomal instability. The clinical consequence is a syndrome dominated by congenital microcephaly, pre- and post-natal growth restriction, a "bird-like" facial appearance, and mild intellectual disability.

The disorder was first defined molecularly in 2009 (Waltes et al., PMID: 19409520) in a single patient who was compound heterozygous for RAD50 mutations. Crucially, that index patient — unlike patients with classic Nijmegen breakage syndrome (NBS, caused by NBN/nibrin mutations) — never had severe infections, had normal immunoglobulin levels, and had not developed lymphoid malignancy by age 23. This distinction (microcephaly and growth failure without the severe immunodeficiency/lymphoma of NBS) is the defining feature of the RAD50 phenotype, although subsequent case reports have broadened the spectrum to include bone-marrow failure and B-cell immunodeficiency in some patients.

Because only a handful of unrelated patients have been reported worldwide since 2009, there are no formal prevalence or incidence figures; every reported variant is "private" (family-specific) with no founder mutation. Diagnosis rests on whole-exome sequencing or DNA-repair gene panels combined with functional confirmation in patient fibroblasts (radiosensitivity, radioresistant DNA synthesis, absent MRN foci, impaired ATM activation, and rescue by wild-type RAD50). Management is entirely supportive: growth and developmental support, surveillance of blood counts and immune function, strict avoidance of ionizing radiation and dose-reduced genotoxic chemotherapy given the radiosensitivity, and allogeneic hematopoietic stem-cell transplantation (HSCT) reserved for those who develop marrow failure. No curative or disease-specific therapy exists. Heterozygous carriers are relevant to counseling because at least one RAD50 loss-of-function allele has been classified as a moderate-risk breast-cancer allele.

1. Disease Information

Overview. NBSLD is a Mendelian DNA-repair-deficiency disorder within the family of chromosomal-instability syndromes that also includes ataxia-telangiectasia (A-T, ATM), ataxia-telangiectasia-like disorder (ATLD, MRE11), and classic Nijmegen breakage syndrome (NBS, NBN/nibrin). All four converge on the MRN–ATM DSB-signaling axis. NBSLD specifically denotes the RAD50-deficiency phenotype, which clinically resembles NBS (microcephaly, bird-like face, growth and mental retardation, cellular radiosensitivity) but is caused by mutations in RAD50 rather than NBN.

Key identifiers.

Resource	Identifier
OMIM	#613078 (Nijmegen breakage syndrome-like disorder)
MONDO	MONDO:0013415
Gene (HGNC)	RAD50, HGNC:9816
NCBI Gene	10111
UniProt	Q92878
Ensembl / locus	5q31.1; RefSeq NM_005732
Orphanet	NBS-like spectrum (chromosomal instability syndromes)

Synonyms / alternative names. RAD50 deficiency; NBS-like disorder; NBSLD; Nijmegen breakage syndrome-like disorder due to RAD50 deficiency.

Information source. The knowledge base is derived almost entirely from aggregated disease-level resources and individual published case reports (a handful of patients worldwide), supplemented by in vitro functional studies of patient-derived cells and model-organism data — not from large EHR cohorts.

2. Etiology

Disease causal factors — genetic. NBSLD is caused by biallelic (homozygous or compound heterozygous) loss-of-function/hypomorphic variants in RAD50. RAD50 is one of three obligate subunits of the MRN complex; when the protein is absent or destabilized, MRN cannot properly sense DSBs or activate ATM. In the index patient, compound heterozygous RAD50 mutations produced only low levels of unstable RAD50 protein, and the cellular defect was fully rescued by expression of wild-type RAD50, establishing RAD50 as the direct cause (PMID: 19409520).

"We found that she is compound heterozygous for mutations in the RAD50 gene that give rise to low levels of unstable RAD50 protein. Cells from the patient were characterized by chromosomal instability; radiosensitivity; failure to form DNA damage-induced MRN foci; and impaired radiation-induced activation of and downstream signaling through the ATM protein." (PMID: 19409520)

Genetic risk factors. The causal variants are the biallelic RAD50 alleles themselves. No independent modifier or susceptibility loci have been established given the tiny patient population.

Environmental risk factors. No environmental cause initiates the disease — it is fully genetic. However, because the defect is in DSB repair, ionizing radiation and radiomimetic/genotoxic chemicals are dangerous exposures that exacerbate genomic instability and should be minimized.

Protective factors. No genetic or environmental protective factors are established. Conceptually, in DSB-repair-deficient microcephaly models, genetic co-deletion of TP53 rescues progenitor cell death (see Mechanism), but this is a mechanistic observation, not a clinical protective factor.

Gene–environment interactions. The principal clinically relevant interaction is genotype × ionizing radiation: RAD50-deficient cells are hypersensitive to radiation, so radiation exposure (diagnostic or therapeutic) produces disproportionate DNA damage and chromosomal instability. This underlies the clinical mandate to avoid radiotherapy and minimize CT imaging.

3. Phenotypes

The core phenotype is remarkably consistent across reported patients, with variable hematologic/immune involvement. Frequencies are qualitative given the tiny cohort.

Phenotype	Type	Suggested HPO term	Onset	Frequency (qualitative)
Microcephaly (often severe/congenital)	Physical/structural	HP:0000252 (Microcephaly); HP:0011451 (Congenital microcephaly)	Congenital/neonatal	Universal
Pre/post-natal growth restriction, short stature	Physical	HP:0001511 (IUGR); HP:0004322 (Short stature)	Prenatal onset	Universal
"Bird-like" face (sloping forehead, midface prominence, receding mandible)	Clinical sign	HP:0000271 (Abnormal facial shape); HP:0000347 (Micrognathia)	Congenital	Common
Mild intellectual disability / developmental delay	Behavioral/cognitive	HP:0001256 (Intellectual disability, mild)	Childhood	Common
Bone-marrow failure	Laboratory/clinical	HP:0005528 (Bone marrow hypocellularity)	Childhood	Variable (subset)
B-cell immunodeficiency / lymphopenia	Laboratory	HP:0005479 (B-cell immunodeficiency); HP:0001888 (Lymphopenia)	Childhood	Variable (subset)
Café-au-lait macules	Physical	HP:0000957 (Café-au-lait spot)	Childhood	Reported
Brachydactyly / skeletal features	Physical	HP:0001156 (Brachydactyly)	Congenital	Reported
Cryptorchidism (bilateral)	Physical	HP:0000028 (Cryptorchidism)	Congenital	Reported (male patient)
Cellular radiosensitivity / chromosomal instability	Laboratory	HP:0003220 (Chromosomal breakage)	Constitutive	Universal (cellular hallmark)

Key distinction from classic NBS. The index patient "never had severe infections, had normal immunoglobulin levels, and did not develop lymphoid malignancy up to age 23 years" (PMID: 19409520). This milder immunologic/oncologic profile separates RAD50 deficiency from NBN-driven NBS. However, Takagi et al. 2023 reported a girl "with microcephaly, mental retardation, bird-like face, short stature, bone marrow failure and B-cell immunodeficiency" (PMID: 37794136), showing hematologic/immune involvement is part of the spectrum in some individuals. Sun et al. 2026 described a 6-year-old boy who "presented with bilateral cryptorchidism, severe microcephaly, growth retardation, multiple café-au-lait macules, brachydactyly, and distinctive craniofacial features, including a sloping forehead, midface prominence, and receding mandible. Mild intellectual impairment was confirmed" (PMID: 41655867).

Progression and severity. Microcephaly and growth restriction are congenital and structurally non-progressive; intellectual disability is generally mild and stable. Marrow failure, when present, is progressive and life-threatening.

Quality-of-life impact. Microcephaly with mild intellectual disability affects educational attainment and independence; short stature affects psychosocial well-being; marrow failure/immunodeficiency (when present) markedly reduce QoL and survival. No formal EQ-5D/SF-36 data exist for this ultra-rare disorder.

4. Genetic / Molecular Information

Causal gene. RAD50 (HGNC:9816; NCBI Gene 10111; UniProt Q92878; locus 5q31.1; RefSeq NM_005732). RAD50 encodes a ~1,312-amino-acid SMC-family ATPase with N- and C-terminal Walker A/B ATPase motifs joined by long antiparallel coiled-coils and a central CXXC zinc-hook that dimerizes RAD50 and tethers the two ends of a broken DNA molecule.

Structural role within MRN. Cryo-EM shows that "MRN senses DSBs through a tight clamp-like sensing state with closed coiled-coil domains, but auto-inhibited MRE11 nuclease. NBS1 wraps around the MRE11 dimer, with NBS1's ATM recruitment motif sequestered by binding to the regulatory RAD50 S site, necessitating a switch in the NBS1 C helix for ATM activation" (PMID: 40968163). RAD50 thus directly gates ATM activation through its regulatory "S site," explaining why RAD50 loss impairs ATM signaling.

Reported pathogenic variants in NBSLD (all biallelic, autosomal recessive, private — no founder):

Patient / study	Variant(s) (protein)	Type	PMID
Waltes 2009 (index)	Compound het; low unstable RAD50 protein	LOF/hypomorphic	19409520
Ragamin 2020	Homozygous c.2524G>A (exon 15) → aberrant splicing/truncation	Splice/LOF	32212377
Takagi 2023	p.Arg83His + p.Glu485Ter	Missense + nonsense	37794136
Sun 2026 (Chinese child)	c.2165_2166insT (p.Lys722Asnfs*6) + c.3752+4_3752+7dup splice	Frameshift + splice	41655867
Novel case 2026	p.His1269Argfs*2 + p.Ser844Asn	Frameshift + missense	41798197

"compound heterozygosity for two variants in RAD50 (NM_005732.3): a paternally inherited frameshift variant c.2165_2166insT (p.Lys722Asnfs6) and a maternally inherited splice-site variant c.3752 + 4_3752 + 7dup"* (PMID: 41655867)

Variant classification & functional consequence. All reported variants are pathogenic/likely-pathogenic loss-of-function or hypomorphic, producing reduced or unstable RAD50 protein — i.e., a loss-of-function mechanism (not gain-of-function or dominant-negative). Splice variants have been confirmed pathogenic by minigene assays and radioresistant DNA synthesis in patient fibroblasts.

Somatic vs germline. All disease-causing variants are germline. (Somatic RAD50/MRN dysregulation is separately implicated in cancer biology but is not the disease mechanism here.)

Modifier genes. None formally established for NBSLD. TP53 dosage is a mechanistic modifier of the downstream apoptotic phenotype in model systems.

Epigenetic information / chromosomal abnormalities. No specific disease-defining methylation signature or large-scale chromosomal rearrangement; the hallmark is acquired chromosomal instability (breaks, radiation-induced aberrations) secondary to defective DSB repair, not a constitutional cytogenetic abnormality.

5. Environmental Information

Environmental factors: No environmental agent causes NBSLD. Ionizing radiation is a hazard that worsens genomic instability in the radiosensitive cells (relevant to diagnostic imaging and radiotherapy).
Lifestyle factors: None established as causal or protective.
Infectious agents: Not applicable as a cause. Recurrent/severe infections may occur secondary to immunodeficiency in the subset with immune involvement.

6. Mechanism / Pathophysiology

Causal chain (upstream → downstream):

Biallelic RAD50 LOF variants
│  (reduced / unstable RAD50 protein)
▼
Destabilized MRE11–RAD50–NBS1 (MRN) complex
│  (cannot sense DSBs; NBS1 ATM-recruitment switch fails)
▼
Failure to form DNA-damage-induced MRN foci
│
▼
Impaired ATM kinase activation & downstream DDR signaling
│
├── Defective G1/S checkpoint
├── Radioresistant DNA synthesis (S-phase checkpoint failure)
├── G2 accumulation
└── Chromosomal instability + cellular radiosensitivity
│
▼
Unrepaired DSBs in rapidly proliferating progenitors
│  (esp. neural progenitor cells)
▼
p53 (TP53)-dependent apoptosis of progenitors
│
▼
Depletion of progenitor pool & reduced tissue growth
│
▼
MICROCEPHALY + GROWTH RESTRICTION (± marrow failure)

Molecular pathways & cellular processes. The central pathway is the MRN–ATM DNA double-strand-break response / DNA damage checkpoint signaling. Suggested GO biological-process terms: GO:0006302 (double-strand break repair), GO:0000724 (DSB repair via homologous recombination), GO:0006281 (DNA repair), GO:0031573 (mitotic intra-S DNA damage checkpoint), GO:0007095 (mitotic G2 DNA damage checkpoint), GO:0042769 (DNA damage response, detection of DNA damage), GO:0006977 (DNA-damage-induced cell cycle arrest by p53), GO:0006915 (apoptotic process).

Protein dysfunction. RAD50 loss is a loss-of-function of a structural ATPase; the MRN clamp cannot adopt the DSB-sensing state and cannot switch NBS1's C-helix to activate ATM (PMID: 40968163). In the index patient, DNA-damage-induced ATM activation was abolished and restored by WT RAD50; Takagi 2023 similarly found "DNA damage-induced activation of the ATM kinase was markedly decreased, which was restored by the expression of wild-type (WT) RAD50" (PMID: 37794136).

Downstream apoptotic mechanism (microcephaly). Evidence from DSB-repair-deficient microcephaly models indicates that unrepaired DSBs in proliferating neural progenitor cells (NPCs) trigger p53-dependent apoptosis, depleting the progenitor pool and producing microcephaly:

In citron-kinase-deficient mice, "in doubly CitK and Trp53 mutant mice, neural progenitor cell death is dramatically reduced; moreover, clinical and neuroanatomical phenotypes are remarkably improved" (PMID: 28199840).
Conditional Ino80 deletion from cortical NPCs "impairs DNA double-strand break (DSB) repair, triggering p53-dependent apoptosis and microcephaly" (PMID: 32737294).

In vivo consequences of MRN dysfunction. Hypomorphic Mre11-complex mouse alleles reveal that "the DNA repair, rather than DDR signaling functions of the complex, is acutely required in the context of ATM deficiency to suppress genome instability and lymphomagenesis" (PMID: 26538284), establishing genome instability and cancer predisposition as in-vivo consequences of MRN/RAD50 dysfunction.

Cell types & compartments. Principally affected cell types: neural progenitor cells (CL:0011020), hematopoietic stem/progenitor cells (CL:0008001), lymphocytes/B cells (CL:0000236). Subcellular compartment: nucleus (GO:0005634); the MRN complex acts at sites of nuclear DNA damage (GO:0035861, site of double-strand break).

Immune involvement. Because MRN/ATM signaling participates in V(D)J recombination and class-switch recombination, RAD50 hypofunction can impair lymphocyte development, producing B-cell immunodeficiency and lymphopenia in a subset (PMID: 37794136).

Molecular profiling. No large-scale transcriptomic/proteomic/metabolomic disease signatures have been published for this ultra-rare disorder; the mechanistic evidence is functional/cell-biological.

7. Anatomical Structures Affected

Primary organs / systems: Central nervous system — brain, especially cerebral cortex (UBERON:0000955 brain; UBERON:0000956 cerebral cortex) → microcephaly. Whole-body growth (skeletal system, UBERON:0002204) → growth restriction/short stature. Craniofacial skeleton → bird-like facies.
Secondary/variable involvement: Bone marrow / hematopoietic system (UBERON:0002371) → marrow failure; immune system (UBERON:0002405) → B-cell immunodeficiency; reproductive (cryptorchidism); skin (café-au-lait macules).
Tissue/cell level: Proliferating progenitor populations — neural progenitors (CL:0011020) and hematopoietic progenitors (CL:0008001) — are most vulnerable because DSB burden is highest in rapidly dividing cells.
Subcellular level: Nucleus (GO:0005634), specifically chromatin at DSB sites (GO:0035861).
Localization / lateralization: Microcephaly is symmetric/bilateral; craniofacial and growth features are generalized and symmetric.

8. Temporal Development

Onset: Congenital. Microcephaly and growth restriction are present prenatally (intrauterine growth restriction) and at birth; developmental delay becomes apparent in early childhood.
Onset pattern: Chronic/constitutive (a developmental disorder, not acute).
Progression: Structural/neurodevelopmental features are static/non-progressive. Intellectual disability is stable and mild. When present, bone-marrow failure is progressive and may be life-limiting. Cellular radiosensitivity and cancer risk are lifelong.
Disease course: Chronic, lifelong.
Critical periods: Prenatal and early-childhood neurodevelopment (window during which progenitor apoptosis determines brain size). Lifelong vulnerability window for radiation-induced damage and malignancy.

9. Inheritance and Population

Inheritance: Autosomal recessive (biallelic RAD50 variants; affected individuals are homozygous or compound heterozygous). Unaffected parents are obligate carriers.
Epidemiology: Ultra-rare. Only a handful of unrelated patients/families reported worldwide since 2009. Sun et al. 2026: "Merely few cases have been reported worldwide, and its phenotypic spectrum remains incompletely defined" (PMID: 41655867). No reliable prevalence or incidence figures exist.
Penetrance / expressivity: Biallelic LOF appears fully penetrant for microcephaly/growth restriction; expressivity is variable for hematologic/immune features (present in some, absent in others).
Founder effects / consanguinity: No founder mutation; all variants are private. Homozygous cases (e.g., Ragamin 2020's splice variant) imply a role for consanguinity/shared ancestry in some families.
Carrier relevance (breast cancer): In a population-based Northern Finnish study (2,343 breast-cancer cases vs 4,607 controls), heterozygous RAD50 loss-of-function was a moderate-risk breast-cancer allele: "CHEK2 c.1100delC, MCPH1 c.909_921del, and RAD50 c.687delT were moderate-risk alleles" (PMID: 40009290). Carriers warrant counseling about cancer risk even though they do not have NBSLD.
Sex ratio: Both sexes affected; no sex bias expected for an autosomal recessive disorder.

10. Diagnostics

Diagnostic approach. Clinical suspicion is triggered by congenital microcephaly, pre/post-natal growth restriction, bird-like facies, and mild intellectual disability. This prompts trio-based whole-exome sequencing (WES) or DNA-repair gene panels, which identify the biallelic RAD50 variants. Splice variants are confirmed by minigene assays (PMID: 41655867); variants are Sanger-validated and segregation-tested in parents (PMID: 41798197).

Functional / cellular confirmation (essential given VUS abundance in a private-variant disease). Patient-derived primary fibroblasts are used to demonstrate: - reduced/absent RAD50 protein by immunoblot; - cellular radiosensitivity (colony-survival assays); - radioresistant DNA synthesis — "Using patient-derived primary fibroblasts, we could show abnormal radioresistant DNA synthesis confirming pathogenicity of the identified variant" (PMID: 32212377); - absent DNA-damage-induced MRN foci; - impaired ATM activation; - rescue by wild-type RAD50 complementation — "The defective cellular phenotype was rescued by wild-type RAD50" (PMID: 19409520).

Laboratory / clinical tests. Complete blood count (cytopenias/marrow failure), immunoglobulin levels and lymphocyte subsets (immunodeficiency), chromosomal breakage studies (spontaneous and radiation-induced), and brain MRI to characterize microcephaly.

Clinical criteria / differential diagnosis. Differential includes classic NBS (NBN), ATLD (MRE11), ataxia-telangiectasia (ATM), LIG4 syndrome, and other microcephalic primordial dwarfism/DSB-repair disorders. Distinguishing features: RAD50 deficiency shows microcephaly + growth failure with generally milder immunodeficiency and (in the index case) no lymphoma, versus prominent immunodeficiency/lymphoma of NBS and the ataxia (without microcephaly) of ATLD.

Screening. No newborn or population screening exists (too rare). Cascade carrier testing of relatives and prenatal/preimplantation testing are options once familial variants are known.

11. Outcome / Prognosis

Survival / life expectancy: Not formally quantified due to rarity. Prognosis is driven by (a) severity of neurodevelopmental impairment, (b) presence of bone-marrow failure/immunodeficiency, and (c) cancer development. Patients without marrow failure or malignancy (e.g., the index patient followed to age 23) can have relatively stable long-term courses.
Morbidity: Mild intellectual disability, short stature, and (variable) immune/hematologic disease. Café-au-lait macules and skeletal features add to the phenotype but are not typically disabling.
Complications: Bone-marrow failure, B-cell immunodeficiency/recurrent infections, and predisposition to malignancy (genome instability). By analogy to MRN-complex dysfunction, lymphomagenesis is a theoretical concern, though the index RAD50 patient had not developed lymphoma by age 23.
Prognostic factors: Presence and severity of marrow failure and immunodeficiency are the key adverse prognostic indicators; radiosensitivity constrains oncologic treatment options.

12. Treatment

There is no curative or disease-specific therapy. Management is supportive and symptom-directed. Suggested MAXO terms in brackets.

Supportive / rehabilitative care: Growth monitoring, developmental and educational support, physical/occupational/speech therapy as indicated [MAXO:0000506 therapeutic intervention]. Surveillance of blood counts and immune function.
Endocrine caution: Recombinant human growth hormone has been tried for short stature, but administering it without prior genetic evaluation is inappropriate — highlighted by a case in which GH was prescribed before the underlying RAD50 diagnosis was recognized (PMID: 41798197). Growth-promoting therapy in a genome-instability disorder must weigh theoretical proliferation/cancer risks.
Hematopoietic stem-cell transplantation (HSCT): Reserved for those who develop bone-marrow failure/immunodeficiency. "Allogeneic hematopoietic stem cell transplantation (HSCT) has been proposed as a potential therapeutic option for DNA damage repair disorders. However, it is not presently required" in patients without marrow failure (PMID: 41655867) [MAXO:0000827 bone marrow transplantation].
Radiation / chemotherapy precautions: Because cells are radiosensitive and chromosomally unstable, ionizing radiation should be minimized/avoided (diagnostic and therapeutic), and radiomimetic/genotoxic chemotherapy dose-reduced if malignancy arises — mirroring reduced-intensity protocols established for classic NBS.
Pharmacogenomics / targeted / gene / cell / RNA therapies: None established for NBSLD. Gene-replacement/gene-editing is conceptually attractive (WT-RAD50 rescues the cellular phenotype in vitro) but not clinically available.

13. Prevention

Primary prevention: Not applicable to disease occurrence (genetic). Genetic counseling for at-risk couples and reproductive options (prenatal diagnosis, preimplantation genetic testing) once familial variants are identified. Avoiding unnecessary ionizing radiation in affected individuals is harm prevention.
Secondary prevention: Cascade testing of relatives; early identification enables surveillance of blood counts/immune function and radiation avoidance before complications arise.
Tertiary prevention: Monitoring for and early management of marrow failure, infections, and malignancy; infection prophylaxis and immunoglobulin support in immunodeficient patients (extrapolated from NBS management).
Counseling: Autosomal-recessive recurrence risk (25% for carrier couples); carrier relatives should be informed of the moderate breast-cancer risk of heterozygous RAD50 LOF (PMID: 40009290).

14. Other Species / Natural Disease

Taxonomy / orthologs: RAD50 is deeply conserved. Orthologs: mouse Rad50 (NCBI Gene 19360), and functional homologs in S. cerevisiae (RAD50) and S. pombe; the MRN/MRX complex is conserved across eukaryotes.
Natural disease in other species: No well-characterized naturally occurring RAD50-deficiency syndrome is documented in companion animals (OMIA) analogous to human NBSLD; the comparative knowledge base is experimental (engineered models) rather than natural disease.
Evolutionary conservation: The MRN complex and its role in DSB sensing/ATM activation are conserved from yeast to humans, making lower-organism studies informative about mechanism.

15. Model Organisms

Mouse (primary model): Complete Rad50 knockout is embryonic lethal, so disease modeling relies on hypomorphic alleles of the Mre11-complex, which model DSB-repair defects, genome instability, and lymphomagenesis, and reveal ATM-independent repair functions: "Hypomorphic alleles of MRE11 and NBS1 confer embryonic lethality in ATM-deficient mice, indicating that the complex exerts ATM-independent functions that are essential when ATM is absent" (PMID: 26538284).
Related MRN models: Transgenic mice expressing reduced wild-type MRN or the MRE11-ATLD1 allele exhibit small body size, anemia, bone-marrow failure, extramedullary hematopoiesis, and impaired lymphocyte development — recapitulating hematopoietic aspects of MRN-deficiency disorders (PMID: 41075274).
Microcephaly models (mechanistic surrogates): Citron-kinase-deficient (PMID: 28199840) and Ino80-deficient (PMID: 32737294) mice recapitulate the DSB-repair-failure → p53-apoptosis → microcephaly axis and, importantly, show TP53 co-deletion rescues progenitor death — supporting the mechanistic model for NBSLD microcephaly.
Lower organisms: S. cerevisiae and S. pombe (Mre11-Rad50-Nbs1/Xrs2 = MRX/MRN) provide conserved insight into DSB processing and ATM(Tel1) regulation.
Model limitations: No mouse fully recapitulates the specific human RAD50-hypomorph NBSLD phenotype; knockout lethality forces reliance on hypomorphs and related-subunit models, and murine models may not capture the milder human neurocognitive phenotype.

Mechanistic Model / Interpretation

NBSLD is best understood as a "DSB-sensing failure" disorder. RAD50 is a structural cornerstone of the MRN clamp that (1) tethers broken DNA ends via its zinc-hook and coiled-coils and (2) gates ATM activation through its regulatory S site controlling NBS1's ATM-recruitment switch. Biallelic hypomorphic RAD50 variants reduce or destabilize the protein, so MRN cannot fold into its DSB-sensing state. The proximal cellular result is loss of DNA-damage-induced MRN foci and blunted ATM activation — directly demonstrated in patient cells and rescued by WT RAD50 in two independent studies (PMID: 19409520; PMID: 37794136).

Downstream, the DDR checkpoint network fails: G1/S checkpoint is defective, DNA synthesis becomes radioresistant, cells accumulate in G2, and chromosomal instability ensues. In the developing organism, the tissues that suffer most are those with the highest proliferative demand — neural and hematopoietic progenitors. Unrepaired DSBs in these progenitors activate p53-dependent apoptosis, depleting the progenitor pool. This is the crux linking a housekeeping DNA-repair defect to the tissue-specific clinical picture of microcephaly and growth restriction, and it is the same paradigm validated genetically (via Trp53 rescue) in independent microcephaly models. The variable hematologic/immune involvement reflects the same progenitor-apoptosis mechanism operating in bone marrow plus impaired MRN/ATM-dependent V(D)J and class-switch recombination.

The distinction from classic NBS is instructive: both diseases hit the same MRN–ATM axis, yet NBN mutations produce prominent immunodeficiency and lymphoma while RAD50 mutations produce a comparatively milder immune/oncologic phenotype (at least in the index patient). This likely reflects subunit-specific residual functions and the particular hypomorphic nature of the reported RAD50 alleles.

Evidence Base

PMID	Study	Contribution
19409520	Waltes 2009 — Human RAD50 deficiency in a NBS-like disorder	Defining paper. Compound-het RAD50, unstable protein, absent MRN foci, impaired ATM, checkpoint failure, chromosomal instability; rescued by WT RAD50.
32212377	Ragamin 2020 — Confirmation of a distinctive phenotype	Homozygous splice variant; radioresistant DNA synthesis confirms pathogenicity.
37794136	Takagi 2023 — Bone marrow failure & immunodeficiency	Expands phenotype; ATM activation decreased, rescued by WT RAD50.
41655867	Sun 2026 — Expanding the mutational spectrum (Chinese child)	New private biallelic variants; documents rarity; HSCT indication.
41798197	2026 case report	Novel variants p.His1269Argfs*2 + p.Ser844Asn; cautionary GH-before-diagnosis narrative.
40968163	Cryo-EM of MRN	Structural basis of DSB sensing and RAD50-gated ATM activation.
26538284	Mre11-complex mouse model	In vivo genome instability/lymphomagenesis; ATM-independent MRN repair functions.
28199840	CitK/Trp53 mice	p53-dependent progenitor apoptosis drives microcephaly; TP53 rescue.
32737294	Ino80 NPC model	DSB-repair failure → p53 apoptosis → microcephaly.
40009290	Finnish breast-cancer study	Heterozygous RAD50 LOF is a moderate breast-cancer risk allele (carrier counseling).
41075274	MRE11-ATLD1 mouse	Low MRN → anemia, marrow failure, impaired lymphocyte development.

Limitations and Knowledge Gaps

Extreme rarity. Only a handful of unrelated patients reported worldwide; conclusions rest on case reports and functional assays, not cohorts. No prevalence, incidence, survival, or QoL data exist.
Private-variant genetics. Every variant is family-specific with no founder allele, complicating variant interpretation and making functional assays essential for diagnosis.
Phenotypic spectrum incompletely defined. Whether marrow failure/immunodeficiency and cancer risk are core or occasional features is unresolved; longer follow-up is needed to establish lifetime malignancy risk.
No dedicated RAD50-hypomorph mouse fully models the human disease; knockout lethality forces reliance on related-subunit and general microcephaly models. The p53-apoptosis causal chain is inferred from analogous DSB-repair models, not proven directly in RAD50-deficient neural tissue.
No omics data. No transcriptomic/proteomic/metabolomic disease signatures exist for NBSLD.
No disease-specific therapy or trials. Management is extrapolated from NBS and general DNA-repair-disorder practice.

Proposed Follow-up Experiments / Actions

International patient registry / natural-history study to aggregate scattered cases and define the true phenotypic spectrum, lifetime cancer risk, and survival.
Standardized functional-assay panel (RAD50 immunoblot, radiosensitivity, radioresistant DNA synthesis, MRN-foci, ATM activation, WT-RAD50 rescue) to classify VUS reproducibly across labs.
RAD50-hypomorph mouse or human iPSC-derived cerebral organoid models carrying patient variants to directly test the p53-dependent progenitor-apoptosis mechanism and evaluate whether p53/apoptosis modulation preserves progenitor pools.
Prospective hematologic/immune surveillance protocol to determine who progresses to marrow failure and to define HSCT timing.
Carrier-counseling guidance integrating the moderate breast-cancer risk of heterozygous RAD50 LOF into family cascade testing.
Careful re-evaluation of growth-hormone use in genome-instability disorders, given the theoretical proliferation/cancer risk and the reported instance of GH prescribed before genetic diagnosis.

Report compiled from 6 confirmed findings and 31 reviewed papers over 5 investigation iterations. Evidence types span human clinical case reports, in vitro patient-cell functional studies, model-organism genetics, and structural biology.

Ask OpenScientist

OpenScientist Report

Classifications

Inheritance

Subtypes

Mechanistic Hypotheses

Discussions and Knowledge Gaps

Pathophysiology

Pathograph

Phenotypes

Genetic Associations

Medical Actions

Differential Diagnoses

Source YAML

References & Deep Research

References

Deep Research

Nijmegen Breakage Syndrome-Like Disorder (RAD50 Deficiency): Comprehensive Research Report

1. Disease Information

2. Etiology

3. Phenotypes

4. Genetic/Molecular Information

5. Environmental Information

6. Mechanism / Pathophysiology

7. Anatomical Structures Affected

8. Temporal Development

9. Inheritance and Population

10. Diagnostics

11. Outcome / Prognosis

12. Treatment

13. Prevention

14. Other Species / Natural Disease

15. Model Organisms

Summary Table of Key Ontology Term Suggestions

Sources

Nijmegen Breakage Syndrome-like Disorder (NBSLD / RAD50 Deficiency): A Comprehensive Disease Characteristics Report

Summary

1. Disease Information

2. Etiology

3. Phenotypes

4. Genetic / Molecular Information

5. Environmental Information

6. Mechanism / Pathophysiology

7. Anatomical Structures Affected

8. Temporal Development

9. Inheritance and Population

10. Diagnostics

11. Outcome / Prognosis

12. Treatment

13. Prevention

14. Other Species / Natural Disease

15. Model Organisms

Mechanistic Model / Interpretation

Evidence Base

Limitations and Knowledge Gaps

Proposed Follow-up Experiments / Actions

Artifacts