Dyskeratosis Congenita Autosomal Recessive 2

Mendelian MONDO:0013519 Pathograph 31 Show in embeddings browser dyskeratosis congenita

Dyskeratosis congenita autosomal recessive 2 (DKCB2) is the telomere biology disorder caused by biallelic variants in NHP2. NHP2 is one of the four core proteins — with dyskerin, NOP10 and GAR1 — that assemble co-transcriptionally on box H/ACA RNAs. The telomerase RNA component TERC carries an H/ACA domain, so the same complex that matures small nucleolar RNAs also binds and stabilises TERC. The disease-associated NHP2 variants do not abolish the protein's catalytic role, because it has none; they compromise its incorporation into the H/ACA ribonucleoprotein, and NHP2 that fails to be incorporated is degraded by the proteasome. TERC steady-state levels fall, telomerase activity falls, and telomeres shorten faster than division can be sustained in the highest-turnover tissues — marrow, mucosa, skin appendages. The clinical picture is that of the dyskeratosis congenita spectrum: bone marrow failure, the mucocutaneous triad of nail dystrophy, reticulate skin pigmentation and oral leukoplakia, and in the reported patients intellectual disability, liver disease, cataracts and intracranial calcification, with malignancy reported in adulthood. Because the H/ACA complex is also required for ribosomal RNA maturation, NHP2 deficiency measurably impairs rRNA biogenesis, which is a candidate explanation for the features that short telomeres alone do not predict. Fewer than ten families have been reported and ClinGen classifies the gene-disease relationship as Limited.

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Mappings
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Inheritance
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Pathophys.
15
Phenotypes
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Gaps
31
Pathograph
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Genes
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Variants
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Medical Actions
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References
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Deep Research
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Classifications

Harrison's Part
GENETICS ENVIRONMENT DISEASE ONCOLOGY HEMATOLOGY
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Mappings

MONDO
MONDO:0013519 dyskeratosis congenita, autosomal recessive 2
skos:exactMatch MONDO
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Inheritance

1
Autosomal recessive inheritance HP:0000007
DKCB2 requires two defective NHP2 alleles; reported genotypes are compound heterozygous and, in a consanguineous family, homozygous. Parents of an affected child are obligate heterozygotes and each future sibling has a 25% recurrence risk. The zygosity line is not purely academic here: heterozygous NHP2 variants have been reported in adults with pulmonary fibrosis and in families with other telomere-biology features, but ClinGen's Interstitial Lung Disease expert panel excluded those heterozygous cases from the gene-disease curation because of population frequencies and incomplete genotyping detail, so an autosomal dominant NHP2 entity is not established.
Autosomal recessive inheritance
Show evidence (3 references)
PMID:20301779 SUPPORT REVIEW SYNTHESIS Other
"Autosomal recessive: CTC1, NHP2, NOP10, POT1, STN1, and WRAP53."
GeneReviews assigns NHP2 to the autosomal recessive group of the telomere biology disorders.
CGGV:assertion_a8fa9dcb-1cc6-43a2-8f86-e6cea0e6fce2-2025-08-01T160000.000Z SUPPORT Other
"The ClinGen Interstitial Lung Disease GCEP has decided to exclude heterozygous cases from this curation due to high population frequencies and/or lack of sufficient detail regarding genotyping."
The reason the curated entity is recessive-only, stated by the panel that made the call.
PMID:40352450 SUPPORT Human Clinical
"Genome sequencing revealed a c.415T>C (p.Tyr139His) disease-causing variant in the NHP2 gene in the index case that was heterozygous in the parents and homozygous in the index case and her older brother."
Segregation in a consanguineous family: unaffected heterozygous parents, two homozygous affected siblings, which is the recessive pattern.
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Discussions and Knowledge Gaps

3
Which of the extra-haematopoietic features of DKCB2 follow from telomere attrition, and which from the ribosomal RNA biogenesis defect?
KNOWLEDGE GAP OPEN gap_dkcb2_rrna_versus_telomere
Attached to
pathophysiology#Ribosomal RNA Biogenesis Impairment pathophysiology#Extra-Hematopoietic Tissue Dysfunction
Intellectual disability, infantile cataract and intracranial calcification are not what a pure short-telomere phenotype predicts, and most people with dyskeratosis congenita have normal neurological function. NHP2 deficiency demonstrably impairs rRNA biogenesis, which makes a ribosomopathy-like arm the obvious candidate, and the authors of the H/ACA assembly study argued in exactly that direction — that some of the disorders in dyskeratosis congenita may come from alteration of H/ACA ribonucleoproteins generally rather than from the telomerase arm alone. Nothing separates the two: no NHP2 patient has had ribosome biogenesis and telomere length measured against the presence or absence of the neurological features, and with four curated probands the cohort to do it in does not exist. The distinction is not academic. A telomere-directed therapy that restored TERC would be expected to help the marrow and leave a ribosomal arm untouched.
Proposed experiments
rRNA processing profiling across NHP2 genotypes
exp_dkcb2_rrna_in_patient_cells
Measure pre-rRNA processing intermediates and telomere length in primary cells from each reported NHP2 genotype, and test whether the magnitude of the rRNA defect tracks the neurological and ocular features rather than the haematological ones.
Would support
pathophysiology#Ribosomal RNA Biogenesis Impairment
What is the cancer risk in biallelic NHP2 disease, and does it differ from the telomere biology disorders generally?
KNOWLEDGE GAP OPEN gap_dkcb2_cancer_risk_unquantified
Attached to
pathophysiology#Clonal Evolution in the Failing Marrow phenotypes#Gastric carcinoma
One myelodysplastic syndrome and one gastric carcinoma have been reported in a single NHP2 patient. That is enough to say the risk is not obviously absent and nowhere near enough to quantify it, or to say whether the tumour spectrum differs from the head-and-neck and anogenital squamous cancers that dominate the disorder family. Cohort studies that produce cumulative cancer incidence for inherited bone marrow failure syndromes are powered on the common genotypes; four probands will not appear in them separately. The practical consequence is that surveillance in DKCB2 has to be prescribed on the disorder-family schedule, which is what this entry does, and that a family asking for a number cannot be given one.
Proposed experiments
Pooled telomere biology disorder registry analysis by gene
exp_dkcb2_registry_pooling
Pool the international inherited bone marrow failure and telomere biology registries and report cancer incidence stratified by causal gene, so that the rare H/ACA-complex genotypes are reported as a group with their own confidence intervals rather than absorbed into an all-genotype figure.
Do heterozygous NHP2 carriers — including the parents of an affected child — have a telomere-related disease risk of their own?
KNOWLEDGE GAP OPEN gap_dkcb2_heterozygote_risk
Attached to
genetic#NHP2
Heterozygous NHP2 variants have been reported in adults with pulmonary fibrosis, and in one of those patients a somatic TERT promoter mutation appeared to give a subset of blood cells a selective advantage, which is the behaviour of a compartment under telomere stress rather than of a neutral carrier state. Against that, ClinGen excluded the heterozygous cases from its curation on the grounds of population frequency and insufficient genotyping detail. Both readings are defensible on the published evidence. It matters at the point of counselling — obligate-carrier parents of a DKCB2 child would be told something different under each — and again when a parent or sibling is considered as a transplant donor.
Proposed experiments
Telomere length and pulmonary phenotyping of obligate NHP2 carriers
exp_dkcb2_carrier_telomere_lengths
Measure leukocyte telomere length and pulmonary function in the obligate heterozygous parents of reported biallelic NHP2 patients, against age-matched controls, and follow them prospectively for interstitial lung disease.
Would support
genetic#NHP2
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Pathophysiology

10
NHP2 Loss and Failed Incorporation into the H/ACA Complex
Biallelic NHP2 variants are missense changes or a stop-loss extension rather than clean nulls, and the lesion they cause is one of assembly rather than of catalysis: NHP2 has no enzymatic activity of its own. Variant NHP2 that cannot compete with wild-type protein for a place in the H/ACA complex is degraded by the proteasome, so the measurable defect in cells is reduced NHP2 protein. The mechanism is understood as loss of function, although ClinGen records that it has not been formally established.
NHP2 hgnc:14377 HUGO Gene Nomenclature Committee (hgnc) Relation: this pathophysiological event involves this gene This pathophysiological event involves NHP2 (hgnc:14377). hgnc:14377 is a gene from the HUGO Gene Nomenclature Committee.
Genetic context variant_origin: GERMLINE functional_impact_category: LOSS_OF_FUNCTION
Downstream
H/ACA Ribonucleoprotein Assembly Failure NHP2 enters the H/ACA complex through NOP10; variants that cannot dock are lost, so the complex assembles less efficiently on its RNA substrates.
Show evidence (2 references)
CGGV:assertion_a8fa9dcb-1cc6-43a2-8f86-e6cea0e6fce2-2025-08-01T160000.000Z SUPPORT Other
"Seven variants (6 missense, and 1 stop-loss extension) have been reported in humans."
The allelic spectrum, which is what makes an assembly defect rather than a null the right description of the lesion.
CGGV:assertion_a8fa9dcb-1cc6-43a2-8f86-e6cea0e6fce2-2025-08-01T160000.000Z SUPPORT Other
"The mechanism is unclear but thought to be LOF."
ClinGen's own hedge on the mechanism, recorded rather than smoothed over.
H/ACA Ribonucleoprotein Assembly Failure
The dyskerin-NOP10-NHP2-NAF1 tetramer assembles on nascent box H/ACA RNAs. Two of the dyskeratosis congenita NHP2 variants, V126M and Y139H, impair the association with NOP10, and the consequence measured in cells is a major defect in pre-ribonucleoprotein assembly on every H/ACA RNA tested, including the H/ACA domain of the telomerase RNA. This is the step that couples a housekeeping RNA-modification complex to telomere biology: the telomerase RNA is an H/ACA RNA, so it fails with the others rather than through a separate telomere-specific route.
box H/ACA snoRNP assembly GO:0000493 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased box H/ACA snoRNP assembly (GO:0000493). GO:0000493 is a biological process from the Gene Ontology. ↓ DECREASED
Downstream
TERC Depletion and Telomerase Insufficiency The H/ACA proteins stabilise TERC; when the complex does not assemble on it, steady-state TERC falls.
Ribosomal RNA Biogenesis Impairment The same complex matures ribosomal RNA, so the assembly defect is not confined to the telomerase arm.
Show evidence (2 references)
PMID:20008900 SUPPORT In Vitro
"In contrast, NHP2 mutations V126M and Y139H impaired association with NOP10, leading to major pre-RNP assembly defects with all H/ACA RNAs tested, including the H/ACA domain of hTR."
The assembly defect measured directly for patient NHP2 alleles, with the telomerase RNA named among the affected substrates.
PMID:20008900 SUPPORT In Vitro
"Altogether, our results suggest that, in addition to major defects in the telomere/telomerase pathways, some of the disorders occurring in DC may be caused by alteration of most H/ACA RNPs, or by only a subset of them."
The authors' own argument that this node has consequences beyond the telomere arm, which is why the second downstream edge is drawn.
TERC Depletion and Telomerase Insufficiency
TERC is the telomerase template and is rate-limiting. Patients with NHP2 variants have low TERC in peripheral blood, as do patients with dyskerin and NOP10 variants, and the novel variants reduce telomerase activity in cell-based assays. The measurement in patient blood is what makes this a human claim rather than an inference from cell lines.
telomerase RNA stabilization GO:0090669 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased telomerase RNA stabilization (GO:0090669). GO:0090669 is a biological process from the Gene Ontology. ↓ DECREASED
telomerase activity GO:0003720 Gene Ontology (GO) Relation: this pathophysiological event involves this molecular function This pathophysiological event involves decreased telomerase activity (GO:0003720). GO:0003720 is a molecular function from the Gene Ontology. ↓ DECREASED
Downstream
Progressive Telomere Attrition Less telomerase means less repeat addition against the end-replication problem, so telomeres shorten with division.
Show evidence (2 references)
PMID:18523010 SUPPORT Human Clinical
"patients with dyskerin, NOP10, and now NHP2 mutations have all been shown to have low levels of telomerase RNA in their peripheral blood, providing direct evidence of their role in telomere maintenance in humans"
The TERC deficit measured in patients rather than in a model system, which the authors themselves offer as the human evidence for the mechanism.
PMID:37440454 SUPPORT In Vitro
"Although still able to support cell viability, both variants reduce the levels of hTR, the telomerase RNA component, and telomerase activity, expanding the panel of NHP2 pathological variants."
Confirms both arms — template level and enzyme activity — for two further patient alleles.
Progressive Telomere Attrition
Without adequate telomerase the end-replication problem is uncompensated and telomeres shorten with every division. In NHP2 patients leukocyte telomeres are short for age, which is the measurement the diagnosis rests on across the telomere biology disorders.
leukocyte CL:0000738 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves leukocyte (CL:0000738). CL:0000738 is a cell type from the Cell Ontology.
telomere maintenance GO:0000723 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased telomere maintenance (GO:0000723). GO:0000723 is a biological process from the Gene Ontology. ↓ DECREASED
Downstream
Telomere-Initiated Replicative Senescence
Short telomere length
Show evidence (1 reference)
PMID:18523010 SUPPORT Human Clinical
"Patients with NHP2 mutations, in common with patients bearing dyskerin and NOP10 mutations had short telomeres and low TERC levels."
Pairs the telomere length and the template deficit in the same patients, which is the observation this node records.
Telomere-Initiated Replicative Senescence
Critically short telomeres are no longer protected and are sensed as DNA double-strand breaks; the resulting persistent damage response enforces replicative senescence or apoptosis. This is the conserved effector the telomere biology disorders converge on, and it is why tissue-level failure in DKCB2 falls first on the compartments with the highest replicative demand rather than on those where NHP2 is most expressed.
DNA damage response GO:0006974 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves increased DNA damage response (GO:0006974). GO:0006974 is a biological process from the Gene Ontology. ↑ INCREASED replicative senescence GO:0090399 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves increased replicative senescence (GO:0090399). GO:0090399 is a biological process from the Gene Ontology. ↑ INCREASED
Downstream
Hematopoietic Stem Cell Exhaustion
Mucocutaneous Epithelial Renewal Failure
Gastric carcinoma The solid tumour in the one reported NHP2 patient is placed on the epithelial side of the cascade rather than on marrow clonal evolution, because the reporting paper attributes the myelodysplasia to clonal haematopoiesis but leaves the gastric cancer unexplained. Telomere-driven genomic instability in a renewing gastric epithelium is the presumed route and has not been shown here.
Show evidence (1 reference)
PMID:37440454 SUPPORT BACKGROUND Other
"telomeres progressively shorten during each cycle of cell division until they reach a critically short length, and cells enter into replicative senescence and/or apoptosis"
States the conserved step this node conforms to. The sentence is the citing paper's review of established telomere biology, not its own result.
Ribosomal RNA Biogenesis Impairment
Box H/ACA ribonucleoproteins pseudouridylate ribosomal RNA, so an assembly defect reaches ribosome biogenesis as well as telomerase. A functional deficiency of human NHP2 demonstrably impairs rRNA biogenesis. This is the branch that makes DKCB2 more than a short-telomere phenotype, and it is the obvious candidate explanation for the features that telomere attrition alone does not predict — the cataracts, the intellectual disability, the intracranial calcification. That link is a hypothesis and not a demonstrated route, which is why the edge below is drawn with unknown intermediates.
ribosome biogenesis GO:0042254 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased ribosome biogenesis (GO:0042254). GO:0042254 is a biological process from the Gene Ontology. ↓ DECREASED
Downstream
Extra-Hematopoietic Tissue Dysfunction No experiment has connected the rRNA defect to the neurological, ocular or hepatic features in an NHP2 patient. The edge is drawn because the alternative — leaving the node unattached — would present the rRNA defect as having no consequence at all, which the severity of the reported phenotypes argues against.
Show evidence (2 references)
PMID:31985013 SUPPORT In Vitro
"Finally, we demonstrate that a functional deficit of human NHP2 affects ribosomal RNA biogenesis."
The measurement of the rRNA arm in human cells.
PMID:37440454 SUPPORT BACKGROUND Other
"It is essential for the maturation of ribosomal RNA (rRNA) and small nuclear RNAs (snoRNAs)"
States the housekeeping role of the complex that makes this branch expected. Background framing in the citing paper, not its own result.
Hematopoietic Stem Cell Exhaustion
The marrow fails first because it has the highest replicative demand and depends on telomerase to meet it. In the reported NHP2 patients this runs from pancytopenia through falling marrow cellularity to transfusion dependence, and in one adult to myelodysplastic syndrome.
hematopoietic stem cell CL:0000037 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves hematopoietic stem cell (CL:0000037). CL:0000037 is a cell type from the Cell Ontology.
Downstream
Bone marrow failure
Pancytopenia
Clonal Evolution in the Failing Marrow
Show evidence (1 reference)
CGGV:assertion_a8fa9dcb-1cc6-43a2-8f86-e6cea0e6fce2-2025-08-01T160000.000Z SUPPORT Other
"NHP2 biallelic variant carriers present with features common to other monogenic telomere biology disorders (TBD) like: oral leukoplakia, reticular skin pigmentation, nail dystrophy, bone marrow failure, intellectual disability, and short telomeres."
ClinGen's summary of what biallelic NHP2 carriers show, marrow failure among it.
Mucocutaneous Epithelial Renewal Failure
Nails, oral mucosa and skin are renewed continuously and fail for the same reason the marrow does. In this genotype the triad is characteristically late — appearing in a child after eight years of systemic disease, and in an adult only as his cytopenia worsened — which is a diagnostic trap rather than a mechanistic difference.
epithelial cell CL:0000066 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves epithelial cell (CL:0000066). CL:0000066 is a cell type from the Cell Ontology.
Downstream
Nail dystrophy
Oral leukoplakia
Reticulated skin pigmentation
Premature graying of hair
Show evidence (1 reference)
PMID:37440454 SUPPORT Human Clinical
"Further clinical investigation revealed nail dystrophies, gray hair, tooth loss and oral leukoplakia with a bone marrow cellularity between 30 and 40%"
The mucocutaneous features appearing alongside declining marrow cellularity in a genetically confirmed NHP2 patient.
Clonal Evolution in the Failing Marrow
A marrow under replicative stress with unprotected chromosome ends selects for clones that tolerate it, and the telomere biology disorders carry a recognised risk of myelodysplastic syndrome and acute myeloid leukaemia. In NHP2 specifically this is a single reported patient with low-risk myelodysplastic syndrome, so the risk is asserted here at the strength of one case plus the disorder-family literature, not as a quantified genotype-specific figure. The gastric carcinoma in that same patient is not placed on this node: the reporting paper keeps the two apart, ascribing the myelodysplasia to clonal haematopoiesis from telomere shortening while leaving the tumour's etiology unknown.
hematopoietic stem cell CL:0000037 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves hematopoietic stem cell (CL:0000037). CL:0000037 is a cell type from the Cell Ontology.
Downstream
Myelodysplasia
Show evidence (2 references)
PMID:37440454 SUPPORT BACKGROUND Other
"Furthermore, TBDs patients show an increased predisposition to hematological malignancies and, more rarely, solid tumors"
The disorder-family malignancy risk, quoted from the citing paper's review of prior work rather than from its own data.
PMID:20301779 SUPPORT REVIEW SYNTHESIS Other
"People with DC/TBD are at increased risk for progressive bone marrow failure (BMF), myelodysplastic syndrome or acute myelogenous leukemia, solid tumors (usually squamous cell carcinoma of the head/neck or anogenital cancer), and pulmonary fibrosis."
The GeneReviews statement of malignancy risk across the telomere biology disorders, which is the basis for surveillance on genotype.
Extra-Hematopoietic Tissue Dysfunction
Liver, brain and lens involvement in the reported NHP2 patients sits outside what marrow-facing telomere attrition explains on its own. Whether these follow from telomere shortening in those tissues, from the rRNA biogenesis defect, or from both is unresolved.
Downstream
Cirrhosis
Intellectual disability
Global developmental delay
Cataract
Cerebral calcification
Show evidence (1 reference)
PMID:40352450 SUPPORT Human Clinical
"she had an 18-year-old brother with cataracts, intellectual disability, liver cirrhosis, pancytopenia, and hypersplenism"
The extra-haematopoietic constellation in a homozygous NHP2 patient, which this node collects.
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Pathograph

Use the checkboxes to hide or show graph categories. Hover nodes for evidence and cross-linked metadata.
Pathograph: causal mechanism network for Dyskeratosis Congenita Autosomal Recessive 2 Interactive directed graph showing how pathophysiology mechanisms, phenotypes, genetic factors and variants, experimental models, environmental triggers, and treatments relate through causal and linked edges.
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Phenotypes

15
Blood 3
Bone marrow failure FREQUENT Bone marrow hypocellularity HP:0005528 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Bone marrow hypocellularity (HP:0005528). HP:0005528 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
CGGV:assertion_a8fa9dcb-1cc6-43a2-8f86-e6cea0e6fce2-2025-08-01T160000.000Z SUPPORT Other
"nail dystrophy, bone marrow failure, intellectual disability, and short telomeres"
Marrow failure in ClinGen's list of what biallelic NHP2 carriers present with.
PMID:37440454 SUPPORT Human Clinical
"which decreased to 10–30% in the following 8 months, with normal karyotype but erythro- and megakaryopoiesis dysplasia, suggesting TBDs"
The rate of marrow decline in one NHP2 patient, with the dysplastic changes.
Pancytopenia FREQUENT HP:0001876 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Pancytopenia (HP:0001876). HP:0001876 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:40352450 SUPPORT Human Clinical
"additional findings that included intellectual disability, liver disease, pancytopenia, nail dystrophy"
Pancytopenia in the index child after eight years of follow-up.
Myelodysplasia OCCASIONAL HP:0002863 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Myelodysplasia (HP:0002863). HP:0002863 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:37440454 SUPPORT Human Clinical
"diagnosed at age 38 with gastric cancer and low-risk MDS, with normal karyotype (46,XY[20])"
Myelodysplastic syndrome in a genetically confirmed NHP2 patient.
Cardiovascular 1
Hypersplenism OCCASIONAL HP:0001971 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Hypersplenism (HP:0001971). HP:0001971 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:40352450 SUPPORT Human Clinical
"an 18-year-old brother with cataracts, intellectual disability, liver cirrhosis, pancytopenia, and hypersplenism"
Hypersplenism in the older affected sibling.
Digestive 2
Cirrhosis OCCASIONAL HP:0001394 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Cirrhosis (HP:0001394). HP:0001394 is a phenotype from the Human Phenotype Ontology.
Sequelae: Hypersplenism
Show evidence (1 reference)
PMID:40352450 SUPPORT Human Clinical
"an 18-year-old brother with cataracts, intellectual disability, liver cirrhosis, pancytopenia, and hypersplenism"
Cirrhosis in the older affected sibling.
Gastric carcinoma OCCASIONAL Stomach cancer HP:0012126 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Stomach cancer (HP:0012126). HP:0012126 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:37440454 SUPPORT Human Clinical
"The index patient with no family history of MDS was diagnosed at age 38 with gastric cancer and low-risk MDS"
Names the gastric cancer and the age at diagnosis in the index NHP2 patient of that report.
Eye 1
Cataract HP:0000518 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Cataract (HP:0000518), qualified as childhood onset. HP:0000518 is a phenotype from the Human Phenotype Ontology.
Onset: CHILDHOOD
Show evidence (1 reference)
PMID:40352450 SUPPORT Human Clinical
"she had an 18-year-old brother with cataracts, intellectual disability, liver cirrhosis, pancytopenia, and hypersplenism"
Cataracts in both affected siblings of the homozygous family.
Head and Neck 1
Oral leukoplakia FREQUENT HP:0002745 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Oral leukoplakia (HP:0002745). HP:0002745 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:37440454 SUPPORT Human Clinical
"Further clinical investigation revealed nail dystrophies, gray hair, tooth loss and oral leukoplakia"
The mucocutaneous features in a confirmed NHP2 patient.
Integument 3
Nail dystrophy FREQUENT HP:0008404 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Nail dystrophy (HP:0008404). HP:0008404 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
CGGV:assertion_a8fa9dcb-1cc6-43a2-8f86-e6cea0e6fce2-2025-08-01T160000.000Z SUPPORT Other
"oral leukoplakia, reticular skin pigmentation, nail dystrophy"
ClinGen's phenotype list for biallelic NHP2 carriers.
Reticulated skin pigmentation FREQUENT HP:0007427 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Reticulated skin pigmentation (HP:0007427). HP:0007427 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:40352450 SUPPORT Human Clinical
"her brother developed nail dystrophy, oral leucoplakia, graying hair, and reticular pigmentation on his neck"
The triad completing itself in late adolescence in an NHP2 homozygote.
Premature graying of hair OCCASIONAL HP:0002216 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Premature graying of hair (HP:0002216). HP:0002216 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:37440454 SUPPORT Human Clinical
"revealed nail dystrophies, gray hair, tooth loss and oral leukoplakia"
Grey hair recorded in an NHP2 patient at 45.
Musculoskeletal 1
Cerebral calcification OCCASIONAL HP:0002514 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Cerebral calcification (HP:0002514). HP:0002514 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:40352450 SUPPORT Human Clinical
"nail dystrophy, multiple foci of calcification on magnetic resonance imaging of the brain"
The imaging finding on follow-up of the index patient.
Nervous System 2
Intellectual disability FREQUENT HP:0001249 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Intellectual disability (HP:0001249). HP:0001249 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
CGGV:assertion_a8fa9dcb-1cc6-43a2-8f86-e6cea0e6fce2-2025-08-01T160000.000Z SUPPORT Other
"bone marrow failure, intellectual disability, and short telomeres"
Intellectual disability in ClinGen's phenotype list for this entity.
PMID:20301779 SUPPORT REVIEW SYNTHESIS Other
"Although most persons with DC/TBD have normal psychomotor development and normal neurologic function, significant developmental delay is present in both forms"
The contrast that makes the neurological involvement in NHP2 patients worth recording rather than assuming.
Global developmental delay HP:0001263 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Global developmental delay (HP:0001263), qualified as infantile onset. HP:0001263 is a phenotype from the Human Phenotype Ontology.
Onset: INFANTILE
Show evidence (1 reference)
PMID:40352450 SUPPORT Human Clinical
"complaints of inability to walk and decreased vision, as well as developmental delay and cataracts"
The presenting complaint at two years of age.
Cellular 1
Short telomere length VERY_FREQUENT HP:0031413 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Short telomere length (HP:0031413). HP:0031413 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:18523010 SUPPORT Human Clinical
"Patients with NHP2 mutations, in common with patients bearing dyskerin and NOP10 mutations had short telomeres and low TERC levels."
Short telomeres measured in the founding NHP2 patients.
🧬

Genetic Associations

1
NHP2
Gene: NHP2 hgnc:14377 HUGO Gene Nomenclature Committee (hgnc) Relation: this disease-associated gene is this gene This disease-associated gene is NHP2 (hgnc:14377). hgnc:14377 is a gene from the HUGO Gene Nomenclature Committee. relationship_type: CAUSATIVE
Show evidence (4 references)
PMID:18523010 SUPPORT Human Clinical
"We have identified previously uncharacterized NHP2 mutations that can cause autosomal recessive dyskeratosis congenita but have not found any GAR1 mutations."
The gene-disease claim as first made, with the negative result for the fourth core protein in the same sentence.
PMID:30472699 SUPPORT Human Clinical
"a patient with NHP2 gene mutation (compound heterozygote for the NHP2 mutations c.376G>A/c.460T>A; amino acid substitutions: p.Val126Met and p.X154Arg) that occurred as a compound heterozygous state"
The compound heterozygous genotype of the long-followed patient.
PMID:40352450 SUPPORT Human Clinical
"Genome sequencing revealed a c.415T>C (p.Tyr139His) disease-causing variant in the NHP2 gene"
The homozygous allele in the consanguineous sibship.
+ 1 more reference
Variants (3)
c.376G>A (p.Val126Met) in trans with c.460T>A (p.Ter154Arg)
Compound heterozygous genotype of a long-followed patient. V126M is one of the two alleles shown to impair NOP10 association; the second is a stop-loss extension.
c.415T>C (p.Tyr139His), homozygous
Homozygous genotype in two siblings of a consanguineous family, with both parents heterozygous. Y139H is the other allele shown to impair NOP10 association and H/ACA pre-ribonucleoprotein assembly.
p.Ala39Thr in trans with p.Thr44Met
Compound heterozygous genotype of an adult with myelodysplastic syndrome and gastric cancer. Both variants sit in the N-terminal region and are mis-incorporated into the H/ACA complex, then degraded by the proteasome.
💊

Medical Actions

6
Hematopoietic cell transplantation
Action: Hematopoietic Cell TransplantationNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Hematopoietic Cell Transplantation (NCIT:C15431). NCIT:C15431 is a clinical intervention from the NCI Thesaurus. NCIT:C15431
Platform: Cell therapy
The only curative option for marrow failure and leukaemia in the telomere biology disorders. The toxicity caveat is not generic: the same telomere defect is present in every tissue the conditioning regimen exposes. The one reported NHP2 patient to be transplanted rejected the first graft and died of Epstein-Barr virus infection after the second.
Mechanism Target:
Hematopoietic Stem Cell Exhaustion — Replaces the exhausted stem cell compartment. It does nothing for the hepatic, neurological, ocular or solid-tumour risk arising in tissues the graft does not reach.
Show evidence (2 references)
PMID:20301779 SUPPORT REVIEW SYNTHESIS Other
"Hematopoietic cell transplantation (HCT) is the only curative treatment for BMF and leukemia, but long-term outcome has historically been poor due to treatment toxicity; if a suitable donor is not available, androgen therapy may be considered for BMF."
The GeneReviews management statement with its toxicity caveat.
PMID:37440454 SUPPORT Human Clinical
"The patient underwent allogeneic bone marrow transplantations but rejected the graft and, after a second transplantation, unfortunately died of Epstein–Barr virus infection."
The transplant outcome in the only reported NHP2 recipient.
Androgen therapy
Action: Androgen TherapyNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Androgen Therapy (NCIT:C15482). NCIT:C15482 is a clinical intervention from the NCI Thesaurus. NCIT:C15482
Platform: Small molecule
Considered for marrow failure when no suitable donor is available. It requires monitoring of blood count, liver function, liver ultrasound and endocrine status — the liver items matter more than usual in a disorder that carries its own hepatic risk. Androgens must not be combined with granulocyte colony-stimulating factor.
Mechanism Target:
Hematopoietic Stem Cell Exhaustion — Improves counts in marrow failure. No NHP2 patient has been reported on androgen therapy, so this is genotype-level management inherited from the disorder family.
Show evidence (2 references)
PMID:20301779 SUPPORT REVIEW SYNTHESIS Other
"the combination of androgens and granulocyte colony-stimulating factor in treatment of BMF (has been associated with splenic rupture)"
The drug-safety warning from the GeneReviews avoidance list.
PMID:20301779 SUPPORT REVIEW SYNTHESIS Other
"if a suitable donor is not available, androgen therapy may be considered for BMF"
The GeneReviews indication for androgen therapy, which places it as the option when transplantation is not available.
Marrow failure surveillance
Action: Supportive CareNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Supportive Care (NCIT:C15747). NCIT:C15747 is a clinical intervention from the NCI Thesaurus. NCIT:C15747
Platform: Other
Complete blood count annually if normal and more often if abnormal, with annual bone marrow aspirate and biopsy. In this genotype the schedule should start at diagnosis and not wait for the mucocutaneous triad, which the reported patients developed years after their cytopenias.
Show evidence (1 reference)
PMID:20301779 SUPPORT REVIEW SYNTHESIS Other
"For BMF: complete blood count (CBC) annually if normal and more often if abnormal; annual bone marrow aspirate and biopsy."
The GeneReviews marrow surveillance schedule.
Cancer surveillance
Action: Supportive CareNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Supportive Care (NCIT:C15747). NCIT:C15747 is a clinical intervention from the NCI Thesaurus. NCIT:C15747
Platform: Other
Monthly self-examination for oral, head and neck cancer, annual screening by an otolaryngologist and a dermatologist, and annual gynaecological examination, with six-monthly dental review and avoidance of smoking and excessive sun exposure. This is the reason cancer predisposition is carried on this entry rather than deferred to the parent: surveillance is recommended on the basis of genotype, and a family given an NHP2 result needs the schedule whether or not a malignancy has yet been reported in that genotype.
Show evidence (1 reference)
PMID:20301779 SUPPORT REVIEW SYNTHESIS Other
"For cancer risk: monthly self-examination for oral, head, and neck cancer; annual cancer screening by an otolaryngologist and dermatologist; annual gynecologic examination."
The GeneReviews cancer surveillance schedule.
Pulmonary function surveillance
Action: Supportive CareNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Supportive Care (NCIT:C15747). NCIT:C15747 is a clinical intervention from the NCI Thesaurus. NCIT:C15747
Platform: Other
Annual pulmonary function testing from diagnosis or from about age eight, when a child can perform the test. Worth noting that interstitial lung disease has not been observed in the biallelic NHP2 entity, so this is disorder-family surveillance rather than a genotype-specific expectation.
Show evidence (2 references)
PMID:20301779 SUPPORT REVIEW SYNTHESIS Other
"For pulmonary fibrosis: annual pulmonary function tests starting either at diagnosis or when the individual can perform the test (often age ~8 years)"
The GeneReviews pulmonary surveillance schedule.
CGGV:assertion_a8fa9dcb-1cc6-43a2-8f86-e6cea0e6fce2-2025-08-01T160000.000Z SUPPORT Other
"but to date ILD has not been observed for this gene-disease entity"
The genotype-specific qualification on the surveillance recommendation above.
Genetic counseling
Action: Genetic CounselingNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Genetic Counseling (NCIT:C15240). NCIT:C15240 is a clinical intervention from the NCI Thesaurus. NCIT:C15240
Platform: Other
Parents of an affected child are obligate carriers with a 25% recurrence risk in each pregnancy. Relatives being considered as transplant donors must be tested — for the familial variants where known, or by telomere length — before donating, because a heterozygous sibling donor may have a telomere defect of their own. Family members should not donate blood if transplantation is contemplated.
Show evidence (1 reference)
PMID:20301779 SUPPORT REVIEW SYNTHESIS Other
"If a relative has signs or symptoms suggestive of DC/TBD or is being evaluated as a potential HCT donor, telomere length testing – or, if the pathogenic variant(s) in the family are known, molecular genetic testing – is warranted."
The GeneReviews evaluation-of-relatives-at-risk statement.
🔬

Biochemical Markers

2
Telomerase RNA component (TERC) level in peripheral blood
Show evidence (1 reference)
PMID:18523010 SUPPORT Human Clinical
"have all been shown to have low levels of telomerase RNA in their peripheral blood, providing direct evidence of their role in telomere maintenance in humans"
The patient-level TERC measurement.
Leukocyte telomere length by flow-FISH
Show evidence (1 reference)
PMID:20301779 SUPPORT REVIEW SYNTHESIS Other
"A majority of individuals with DC/TBD have abnormally short telomeres for their age, as determined by multicolor flow cytometry fluorescence in situ hybridization (flow-FISH) on lymphocyte subsets."
The GeneReviews diagnostic-testing statement.
📈

Progression

4
Early childhood presentation
The reported paediatric presentations are not the classic triad. In the consanguineous sibship the index patient came to attention at two years with inability to walk, decreased vision from cataracts and developmental delay, and nail, mucosal and skin findings were not reported at presentation. ClinGen records ages of onset in both childhood and adulthood for this gene-disease entity, so a normal mucocutaneous examination in a young child does not argue against the diagnosis.
Show evidence (2 references)
PMID:40352450 SUPPORT Human Clinical
"A two-year-old girl (index patient) was admitted to our hospital with complaints of inability to walk and decreased vision, as well as developmental delay and cataracts."
The presenting picture at two years, which is neurological and ophthalmic rather than haematological or mucocutaneous.
CGGV:assertion_a8fa9dcb-1cc6-43a2-8f86-e6cea0e6fce2-2025-08-01T160000.000Z SUPPORT Other
"4 probands with ages of onset being reported in both childhood and adulthood"
The age-of-onset range across the curated probands.
Mucocutaneous triad emerging after the systemic features
The triad is a late sign in this genotype rather than the entry point. Followed for eight years, the index child accumulated intellectual disability, liver disease, pancytopenia, nail dystrophy and multiple foci of intracranial calcification; her brother, already eighteen at presentation with cataracts, intellectual disability, cirrhosis, pancytopenia and hypersplenism, developed nail dystrophy, oral leukoplakia, greying hair and reticulate neck pigmentation only in the two years before the report. For a paediatrician this is the practical point of the entry: waiting for the triad postpones the diagnosis past the onset of marrow failure and liver disease.
Show evidence (1 reference)
PMID:40352450 SUPPORT Human Clinical
"After 8 years of follow-up, the index patient was identified with additional findings that included intellectual disability, liver disease, pancytopenia, nail dystrophy, multiple foci of calcification on magnetic resonance imaging of the brain, while over the past 2 years, her brother developed..."
Dates the appearance of the mucocutaneous features relative to the systemic ones within a single family.
Adult-onset marrow failure and malignancy
At the other end of the reported range, one compound heterozygote was diagnosed at 38 with gastric cancer and low-risk myelodysplastic syndrome and only later, as the cytopenia worsened, showed nail dystrophy, grey hair, tooth loss and oral leukoplakia with falling marrow cellularity. He died of Epstein-Barr virus infection after a second allogeneic transplant.
Show evidence (1 reference)
PMID:37440454 SUPPORT Human Clinical
"The index patient with no family history of MDS was diagnosed at age 38 with gastric cancer and low-risk MDS, with normal karyotype (46,XY[20])."
The adult end of the reported onset range, in a confirmed NHP2 patient.
Hoyeraal-Hreidarsson severity
Biallelic NHP2 missense variants have also produced Hoyeraal-Hreidarsson syndrome, the severe end of the dyskeratosis congenita spectrum, in one reported case. The individual Hoyeraal-Hreidarsson features in that patient are not curated as phenotypes of this entry because the abstract available for that report does not enumerate them.
Show evidence (1 reference)
PMID:31985013 SUPPORT Human Clinical
"Here, we report the first case of Høyeraal-Hreidarsson syndrome, the severe form of DC, caused by biallelic missense mutations in NHP2."
Establishes that the genotype can reach the severe end of the spectrum, without importing features the source does not list.
📊

Prevalence

1
Unrelated telomere biology disorder patients reported worldwide
Cases In Literature Ultra Rare
Seven pathogenic NHP2 variants had been reported in unrelated patients as of the 2023 review, and ClinGen counted four probands across three publications with case-level data at its 2025 reappraisal. No population prevalence has been published, and no denominator exists from which one could be derived.
Show evidence (2 references)
PMID:37440454 SUPPORT BACKGROUND Human Clinical
"In particular, seven different pathogenic NHP2 (OMIM #613987) variants have been identified in unrelated TBDs patients"
The published variant count. The sentence is this paper's introduction summarising the prior literature rather than its own result.
CGGV:assertion_a8fa9dcb-1cc6-43a2-8f86-e6cea0e6fce2-2025-08-01T160000.000Z SUPPORT Other
"Evidence supporting this gene-disease relationship includes case-level data from 3 different publications describing a total of 4 probands"
The proband count ClinGen was able to use, which is the best available statement of how much of this disease has been observed.
{ }

Source YAML

click to show 
name: Dyskeratosis Congenita Autosomal Recessive 2
creation_date: "2026-09-24T18:00:00Z"
category: Mendelian
description: >-
  Dyskeratosis congenita autosomal recessive 2 (DKCB2) is the telomere biology
  disorder caused by biallelic variants in NHP2. NHP2 is one of the four core
  proteins — with dyskerin, NOP10 and GAR1 — that assemble co-transcriptionally
  on box H/ACA RNAs. The telomerase RNA component TERC carries an H/ACA domain,
  so the same complex that matures small nucleolar RNAs also binds and stabilises
  TERC. The disease-associated NHP2 variants do not abolish the protein's
  catalytic role, because it has none; they compromise its incorporation into the
  H/ACA ribonucleoprotein, and NHP2 that fails to be incorporated is degraded by
  the proteasome. TERC steady-state levels fall, telomerase activity falls, and
  telomeres shorten faster than division can be sustained in the
  highest-turnover tissues — marrow, mucosa, skin appendages. The clinical
  picture is that of the dyskeratosis congenita spectrum: bone marrow failure,
  the mucocutaneous triad of nail dystrophy, reticulate skin pigmentation and
  oral leukoplakia, and in the reported patients intellectual disability, liver
  disease, cataracts and intracranial calcification, with malignancy reported in
  adulthood. Because the H/ACA complex is also required for ribosomal RNA
  maturation, NHP2 deficiency measurably impairs rRNA biogenesis, which is a
  candidate explanation for the features that short telomeres alone do not
  predict. Fewer than ten families have been reported and ClinGen classifies the
  gene-disease relationship as Limited.
synonyms:
- DKCB2
- dyskeratosis congenita, autosomal recessive 2
- NHP2-related dyskeratosis congenita
- NOLA2-related dyskeratosis congenita
disease_term:
  preferred_term: dyskeratosis congenita, autosomal recessive 2
  term:
    id: MONDO:0013519
    label: dyskeratosis congenita, autosomal recessive 2
mappings:
  mondo_mappings:
  - term:
      id: MONDO:0013519
      label: dyskeratosis congenita, autosomal recessive 2
    mapping_predicate: skos:exactMatch
    mapping_source: MONDO
parents:
- dyskeratosis congenita
classifications:
  harrisons_chapter:
  - classification_value: GENETICS_ENVIRONMENT_DISEASE
  - classification_value: ONCOLOGY_HEMATOLOGY
inheritance:
- name: Autosomal recessive inheritance
  inheritance_term:
    preferred_term: Autosomal recessive inheritance
    term:
      id: HP:0000007
      label: Autosomal recessive inheritance
  description: >-
    DKCB2 requires two defective NHP2 alleles; reported genotypes are compound
    heterozygous and, in a consanguineous family, homozygous. Parents of an
    affected child are obligate heterozygotes and each future sibling has a 25%
    recurrence risk. The zygosity line is not purely academic here: heterozygous
    NHP2 variants have been reported in adults with pulmonary fibrosis and in
    families with other telomere-biology features, but ClinGen's Interstitial
    Lung Disease expert panel excluded those heterozygous cases from the
    gene-disease curation because of population frequencies and incomplete
    genotyping detail, so an autosomal dominant NHP2 entity is not established.
  evidence:
  - reference: PMID:20301779
    reference_title: Dyskeratosis Congenita and Related Telomere Biology Disorders.
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      Autosomal recessive: CTC1, NHP2, NOP10, POT1, STN1, and WRAP53.
    explanation: >-
      GeneReviews assigns NHP2 to the autosomal recessive group of the telomere
      biology disorders.
  - reference: CGGV:assertion_a8fa9dcb-1cc6-43a2-8f86-e6cea0e6fce2-2025-08-01T160000.000Z
    reference_title: NHP2 / dyskeratosis congenita, autosomal recessive 2 (Limited)
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      The ClinGen Interstitial Lung Disease GCEP has decided to exclude
      heterozygous cases from this curation due to high population frequencies
      and/or lack of sufficient detail regarding genotyping.
    explanation: >-
      The reason the curated entity is recessive-only, stated by the panel that
      made the call.
  - reference: PMID:40352450
    reference_title: "Siblings with a Homozygous Variant in the NHP2 Gene: A Case Report and Review of Literature."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Genome sequencing revealed a c.415T>C (p.Tyr139His) disease-causing variant
      in the NHP2 gene in the index case that was heterozygous in the parents and
      homozygous in the index case and her older brother.
    explanation: >-
      Segregation in a consanguineous family: unaffected heterozygous parents,
      two homozygous affected siblings, which is the recessive pattern.
prevalence:
- population: Unrelated telomere biology disorder patients reported worldwide
  measure_type: CASES_IN_LITERATURE
  prevalence_class: ULTRA_RARE
  notes: >-
    Seven pathogenic NHP2 variants had been reported in unrelated patients as of
    the 2023 review, and ClinGen counted four probands across three publications
    with case-level data at its 2025 reappraisal. No population prevalence has
    been published, and no denominator exists from which one could be derived.
  evidence:
  - reference: PMID:37440454
    reference_title: "Novel pathological variants of NHP2 affect N-terminal domain flexibility, protein stability, H/ACA Ribonucleoprotein (RNP) complex formation and telomerase activity."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: BACKGROUND
    snippet: >-
      In particular, seven different pathogenic NHP2 (OMIM #613987) variants have
      been identified in unrelated TBDs patients
    explanation: >-
      The published variant count. The sentence is this paper's introduction
      summarising the prior literature rather than its own result.
  - reference: CGGV:assertion_a8fa9dcb-1cc6-43a2-8f86-e6cea0e6fce2-2025-08-01T160000.000Z
    reference_title: NHP2 / dyskeratosis congenita, autosomal recessive 2 (Limited)
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Evidence supporting this gene-disease relationship includes case-level data
      from 3 different publications describing a total of 4 probands
    explanation: >-
      The proband count ClinGen was able to use, which is the best available
      statement of how much of this disease has been observed.
progression:
- phase: Early childhood presentation
  notes: >-
    The reported paediatric presentations are not the classic triad. In the
    consanguineous sibship the index patient came to attention at two years with
    inability to walk, decreased vision from cataracts and developmental delay,
    and nail, mucosal and skin findings were not reported at presentation. ClinGen
    records ages of onset in both childhood and adulthood for this gene-disease
    entity, so a normal mucocutaneous examination in a young child does not argue
    against the diagnosis.
  evidence:
  - reference: PMID:40352450
    reference_title: "Siblings with a Homozygous Variant in the NHP2 Gene: A Case Report and Review of Literature."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      A two-year-old girl (index patient) was admitted to our hospital with
      complaints of inability to walk and decreased vision, as well as
      developmental delay and cataracts.
    explanation: >-
      The presenting picture at two years, which is neurological and ophthalmic
      rather than haematological or mucocutaneous.
  - reference: CGGV:assertion_a8fa9dcb-1cc6-43a2-8f86-e6cea0e6fce2-2025-08-01T160000.000Z
    reference_title: NHP2 / dyskeratosis congenita, autosomal recessive 2 (Limited)
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      4 probands with ages of onset being reported in both childhood and
      adulthood
    explanation: The age-of-onset range across the curated probands.
- phase: Mucocutaneous triad emerging after the systemic features
  notes: >-
    The triad is a late sign in this genotype rather than the entry point.
    Followed for eight years, the index child accumulated intellectual
    disability, liver disease, pancytopenia, nail dystrophy and multiple foci of
    intracranial calcification; her brother, already eighteen at presentation
    with cataracts, intellectual disability, cirrhosis, pancytopenia and
    hypersplenism, developed nail dystrophy, oral leukoplakia, greying hair and
    reticulate neck pigmentation only in the two years before the report. For a
    paediatrician this is the practical point of the entry: waiting for the triad
    postpones the diagnosis past the onset of marrow failure and liver disease.
  evidence:
  - reference: PMID:40352450
    reference_title: "Siblings with a Homozygous Variant in the NHP2 Gene: A Case Report and Review of Literature."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      After 8 years of follow-up, the index patient was identified with
      additional findings that included intellectual disability, liver disease,
      pancytopenia, nail dystrophy, multiple foci of calcification on magnetic
      resonance imaging of the brain, while over the past 2 years, her brother
      developed nail dystrophy, oral leucoplakia, graying hair, and reticular
      pigmentation on his neck.
    explanation: >-
      Dates the appearance of the mucocutaneous features relative to the systemic
      ones within a single family.
- phase: Adult-onset marrow failure and malignancy
  notes: >-
    At the other end of the reported range, one compound heterozygote was
    diagnosed at 38 with gastric cancer and low-risk myelodysplastic syndrome and
    only later, as the cytopenia worsened, showed nail dystrophy, grey hair,
    tooth loss and oral leukoplakia with falling marrow cellularity. He died of
    Epstein-Barr virus infection after a second allogeneic transplant.
  evidence:
  - reference: PMID:37440454
    reference_title: "Novel pathological variants of NHP2 affect N-terminal domain flexibility, protein stability, H/ACA Ribonucleoprotein (RNP) complex formation and telomerase activity."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The index patient with no family history of MDS was diagnosed at age 38
      with gastric cancer and low-risk MDS, with normal karyotype (46,XY[20]).
    explanation: The adult end of the reported onset range, in a confirmed NHP2 patient.
- phase: Hoyeraal-Hreidarsson severity
  notes: >-
    Biallelic NHP2 missense variants have also produced Hoyeraal-Hreidarsson
    syndrome, the severe end of the dyskeratosis congenita spectrum, in one
    reported case. The individual Hoyeraal-Hreidarsson features in that patient
    are not curated as phenotypes of this entry because the abstract available
    for that report does not enumerate them.
  evidence:
  - reference: PMID:31985013
    reference_title: NHP2 deficiency impairs rRNA biogenesis and causes pulmonary fibrosis and Høyeraal-Hreidarsson syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Here, we report the first case of Høyeraal-Hreidarsson syndrome, the severe
      form of DC, caused by biallelic missense mutations in NHP2.
    explanation: >-
      Establishes that the genotype can reach the severe end of the spectrum,
      without importing features the source does not list.
pathophysiology:
- name: NHP2 Loss and Failed Incorporation into the H/ACA Complex
  biological_scale: MOLECULAR
  description: >-
    Biallelic NHP2 variants are missense changes or a stop-loss extension rather
    than clean nulls, and the lesion they cause is one of assembly rather than of
    catalysis: NHP2 has no enzymatic activity of its own. Variant NHP2 that
    cannot compete with wild-type protein for a place in the H/ACA complex is
    degraded by the proteasome, so the measurable defect in cells is reduced NHP2
    protein. The mechanism is understood as loss of function, although ClinGen
    records that it has not been formally established.
  genes:
  - preferred_term: NHP2
    term:
      id: hgnc:14377
      label: NHP2
  genetic_context:
    variant_origin: GERMLINE
    functional_impact_category: LOSS_OF_FUNCTION
  downstream:
  - target: H/ACA Ribonucleoprotein Assembly Failure
    causal_link_type: DIRECT
    description: >-
      NHP2 enters the H/ACA complex through NOP10; variants that cannot dock are
      lost, so the complex assembles less efficiently on its RNA substrates.
    evidence:
    - reference: PMID:37440454
      reference_title: "Novel pathological variants of NHP2 affect N-terminal domain flexibility, protein stability, H/ACA Ribonucleoprotein (RNP) complex formation and telomerase activity."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        Furthermore, both variants fail to be incorporated in the H/ACA RNA
        binding complex when in competition with wild-type endogenous NHP2, and
        the lack of incorporation causes their drastic proteasomal degradation.
      explanation: >-
        The two steps of this edge measured in the same experiment: failure of
        incorporation, then destruction of what was not incorporated.
  evidence:
  - reference: CGGV:assertion_a8fa9dcb-1cc6-43a2-8f86-e6cea0e6fce2-2025-08-01T160000.000Z
    reference_title: NHP2 / dyskeratosis congenita, autosomal recessive 2 (Limited)
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Seven variants (6 missense, and 1 stop-loss extension) have been reported
      in humans.
    explanation: >-
      The allelic spectrum, which is what makes an assembly defect rather than a
      null the right description of the lesion.
  - reference: CGGV:assertion_a8fa9dcb-1cc6-43a2-8f86-e6cea0e6fce2-2025-08-01T160000.000Z
    reference_title: NHP2 / dyskeratosis congenita, autosomal recessive 2 (Limited)
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      The mechanism is unclear but thought to be LOF.
    explanation: >-
      ClinGen's own hedge on the mechanism, recorded rather than smoothed over.
- name: H/ACA Ribonucleoprotein Assembly Failure
  biological_scale: MOLECULAR
  description: >-
    The dyskerin-NOP10-NHP2-NAF1 tetramer assembles on nascent box H/ACA RNAs.
    Two of the dyskeratosis congenita NHP2 variants, V126M and Y139H, impair the
    association with NOP10, and the consequence measured in cells is a major
    defect in pre-ribonucleoprotein assembly on every H/ACA RNA tested, including
    the H/ACA domain of the telomerase RNA. This is the step that couples a
    housekeeping RNA-modification complex to telomere biology: the telomerase RNA
    is an H/ACA RNA, so it fails with the others rather than through a separate
    telomere-specific route.
  biological_processes:
  - preferred_term: box H/ACA snoRNP assembly
    modifier: DECREASED
    term:
      id: GO:0000493
      label: box H/ACA snoRNP assembly
  downstream:
  - target: TERC Depletion and Telomerase Insufficiency
    causal_link_type: DIRECT
    description: >-
      The H/ACA proteins stabilise TERC; when the complex does not assemble on
      it, steady-state TERC falls.
    evidence:
    - reference: PMID:18523010
      reference_title: Mutations in the telomerase component NHP2 cause the premature ageing syndrome dyskeratosis congenita.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        SiRNA-mediated knockdown of NHP2 in human cells led to low TERC levels,
        but this reduction was not observed after GAR1 knockdown.
      explanation: >-
        Isolates NHP2 as the component whose loss lowers TERC, with GAR1
        knockdown as the internal negative control.
  - target: Ribosomal RNA Biogenesis Impairment
    causal_link_type: DIRECT
    description: >-
      The same complex matures ribosomal RNA, so the assembly defect is not
      confined to the telomerase arm.
  evidence:
  - reference: PMID:20008900
    reference_title: "Effects of dyskeratosis congenita mutations in dyskerin, NHP2 and NOP10 on assembly of H/ACA pre-RNPs."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      In contrast, NHP2 mutations V126M and Y139H impaired association with
      NOP10, leading to major pre-RNP assembly defects with all H/ACA RNAs
      tested, including the H/ACA domain of hTR.
    explanation: >-
      The assembly defect measured directly for patient NHP2 alleles, with the
      telomerase RNA named among the affected substrates.
  - reference: PMID:20008900
    reference_title: "Effects of dyskeratosis congenita mutations in dyskerin, NHP2 and NOP10 on assembly of H/ACA pre-RNPs."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Altogether, our results suggest that, in addition to major defects in the
      telomere/telomerase pathways, some of the disorders occurring in DC may be
      caused by alteration of most H/ACA RNPs, or by only a subset of them.
    explanation: >-
      The authors' own argument that this node has consequences beyond the
      telomere arm, which is why the second downstream edge is drawn.
- name: TERC Depletion and Telomerase Insufficiency
  biological_scale: MOLECULAR
  description: >-
    TERC is the telomerase template and is rate-limiting. Patients with NHP2
    variants have low TERC in peripheral blood, as do patients with dyskerin and
    NOP10 variants, and the novel variants reduce telomerase activity in
    cell-based assays. The measurement in patient blood is what makes this a
    human claim rather than an inference from cell lines.
  biological_processes:
  - preferred_term: telomerase RNA stabilization
    modifier: DECREASED
    term:
      id: GO:0090669
      label: telomerase RNA stabilization
  molecular_functions:
  - preferred_term: telomerase activity
    modifier: DECREASED
    term:
      id: GO:0003720
      label: telomerase activity
  downstream:
  - target: Progressive Telomere Attrition
    causal_link_type: DIRECT
    description: >-
      Less telomerase means less repeat addition against the end-replication
      problem, so telomeres shorten with division.
  evidence:
  - reference: PMID:18523010
    reference_title: Mutations in the telomerase component NHP2 cause the premature ageing syndrome dyskeratosis congenita.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      patients with dyskerin, NOP10, and now NHP2 mutations have all been shown
      to have low levels of telomerase RNA in their peripheral blood, providing
      direct evidence of their role in telomere maintenance in humans
    explanation: >-
      The TERC deficit measured in patients rather than in a model system, which
      the authors themselves offer as the human evidence for the mechanism.
  - reference: PMID:37440454
    reference_title: "Novel pathological variants of NHP2 affect N-terminal domain flexibility, protein stability, H/ACA Ribonucleoprotein (RNP) complex formation and telomerase activity."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Although still able to support cell viability, both variants reduce the
      levels of hTR, the telomerase RNA component, and telomerase activity,
      expanding the panel of NHP2 pathological variants.
    explanation: >-
      Confirms both arms — template level and enzyme activity — for two further
      patient alleles.
- name: Progressive Telomere Attrition
  biological_scale: CELLULAR
  conforms_to: "telomere_attrition#Progressive Telomere Attrition"
  description: >-
    Without adequate telomerase the end-replication problem is uncompensated and
    telomeres shorten with every division. In NHP2 patients leukocyte telomeres
    are short for age, which is the measurement the diagnosis rests on across the
    telomere biology disorders.
  cell_types:
  - preferred_term: leukocyte
    term:
      id: CL:0000738
      label: leukocyte
  biological_processes:
  - preferred_term: telomere maintenance
    modifier: DECREASED
    term:
      id: GO:0000723
      label: telomere maintenance
  downstream:
  - target: Telomere-Initiated Replicative Senescence
    causal_link_type: DIRECT
  - target: Short telomere length
    causal_link_type: DIRECT
  evidence:
  - reference: PMID:18523010
    reference_title: Mutations in the telomerase component NHP2 cause the premature ageing syndrome dyskeratosis congenita.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Patients with NHP2 mutations, in common with patients bearing dyskerin and
      NOP10 mutations had short telomeres and low TERC levels.
    explanation: >-
      Pairs the telomere length and the template deficit in the same patients,
      which is the observation this node records.
- name: Telomere-Initiated Replicative Senescence
  biological_scale: CELLULAR
  conforms_to: "telomere_attrition#Telomere-Initiated DNA Damage and Replicative Senescence"
  description: >-
    Critically short telomeres are no longer protected and are sensed as DNA
    double-strand breaks; the resulting persistent damage response enforces
    replicative senescence or apoptosis. This is the conserved effector the
    telomere biology disorders converge on, and it is why tissue-level failure in
    DKCB2 falls first on the compartments with the highest replicative demand
    rather than on those where NHP2 is most expressed.
  biological_processes:
  - preferred_term: DNA damage response
    modifier: INCREASED
    term:
      id: GO:0006974
      label: DNA damage response
  - preferred_term: replicative senescence
    modifier: INCREASED
    term:
      id: GO:0090399
      label: replicative senescence
  downstream:
  - target: Hematopoietic Stem Cell Exhaustion
    causal_link_type: DIRECT
  - target: Mucocutaneous Epithelial Renewal Failure
    causal_link_type: DIRECT
  - target: Gastric carcinoma
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      The solid tumour in the one reported NHP2 patient is placed on the
      epithelial side of the cascade rather than on marrow clonal evolution,
      because the reporting paper attributes the myelodysplasia to clonal
      haematopoiesis but leaves the gastric cancer unexplained. Telomere-driven
      genomic instability in a renewing gastric epithelium is the presumed route
      and has not been shown here.
    evidence:
    - reference: PMID:37440454
      reference_title: "Novel pathological variants of NHP2 affect N-terminal domain flexibility, protein stability, H/ACA Ribonucleoprotein (RNP) complex formation and telomerase activity."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        while MDS may have occurred due to clonal hematopoiesis caused by
        telomere shortening, as previously reported (9), the etiology of the
        gastric cancer remains unknown
      explanation: >-
        The reporting authors separate the two malignancies: the marrow disease
        is ascribed to clonal haematopoiesis, the gastric cancer is not
        mechanistically accounted for, which is why this edge is typed as having
        unknown intermediates.
  evidence:
  - reference: PMID:37440454
    reference_title: "Novel pathological variants of NHP2 affect N-terminal domain flexibility, protein stability, H/ACA Ribonucleoprotein (RNP) complex formation and telomerase activity."
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: BACKGROUND
    snippet: >-
      telomeres progressively shorten during each cycle of cell division until
      they reach a critically short length, and cells enter into replicative
      senescence and/or apoptosis
    explanation: >-
      States the conserved step this node conforms to. The sentence is the citing
      paper's review of established telomere biology, not its own result.
- name: Ribosomal RNA Biogenesis Impairment
  biological_scale: MOLECULAR
  description: >-
    Box H/ACA ribonucleoproteins pseudouridylate ribosomal RNA, so an assembly
    defect reaches ribosome biogenesis as well as telomerase. A functional
    deficiency of human NHP2 demonstrably impairs rRNA biogenesis. This is the
    branch that makes DKCB2 more than a short-telomere phenotype, and it is the
    obvious candidate explanation for the features that telomere attrition alone
    does not predict — the cataracts, the intellectual disability, the
    intracranial calcification. That link is a hypothesis and not a demonstrated
    route, which is why the edge below is drawn with unknown intermediates.
  biological_processes:
  - preferred_term: ribosome biogenesis
    modifier: DECREASED
    term:
      id: GO:0042254
      label: ribosome biogenesis
  downstream:
  - target: Extra-Hematopoietic Tissue Dysfunction
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      No experiment has connected the rRNA defect to the neurological, ocular or
      hepatic features in an NHP2 patient. The edge is drawn because the
      alternative — leaving the node unattached — would present the rRNA defect
      as having no consequence at all, which the severity of the reported
      phenotypes argues against.
  evidence:
  - reference: PMID:31985013
    reference_title: NHP2 deficiency impairs rRNA biogenesis and causes pulmonary fibrosis and Høyeraal-Hreidarsson syndrome.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Finally, we demonstrate that a functional deficit of human NHP2 affects
      ribosomal RNA biogenesis.
    explanation: The measurement of the rRNA arm in human cells.
  - reference: PMID:37440454
    reference_title: "Novel pathological variants of NHP2 affect N-terminal domain flexibility, protein stability, H/ACA Ribonucleoprotein (RNP) complex formation and telomerase activity."
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: BACKGROUND
    snippet: >-
      It is essential for the maturation of ribosomal RNA (rRNA) and small
      nuclear RNAs (snoRNAs)
    explanation: >-
      States the housekeeping role of the complex that makes this branch
      expected. Background framing in the citing paper, not its own result.
- name: Hematopoietic Stem Cell Exhaustion
  biological_scale: TISSUE
  description: >-
    The marrow fails first because it has the highest replicative demand and
    depends on telomerase to meet it. In the reported NHP2 patients this runs
    from pancytopenia through falling marrow cellularity to transfusion
    dependence, and in one adult to myelodysplastic syndrome.
  cell_types:
  - preferred_term: hematopoietic stem cell
    term:
      id: CL:0000037
      label: hematopoietic stem cell
  downstream:
  - target: Bone marrow failure
    causal_link_type: DIRECT
  - target: Pancytopenia
    causal_link_type: DIRECT
  - target: Clonal Evolution in the Failing Marrow
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
  evidence:
  - reference: CGGV:assertion_a8fa9dcb-1cc6-43a2-8f86-e6cea0e6fce2-2025-08-01T160000.000Z
    reference_title: NHP2 / dyskeratosis congenita, autosomal recessive 2 (Limited)
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      NHP2 biallelic variant carriers present with features common to other
      monogenic telomere biology disorders (TBD) like: oral leukoplakia,
      reticular skin pigmentation, nail dystrophy, bone marrow failure,
      intellectual disability, and short telomeres.
    explanation: >-
      ClinGen's summary of what biallelic NHP2 carriers show, marrow failure
      among it.
- name: Mucocutaneous Epithelial Renewal Failure
  biological_scale: TISSUE
  description: >-
    Nails, oral mucosa and skin are renewed continuously and fail for the same
    reason the marrow does. In this genotype the triad is characteristically late
    — appearing in a child after eight years of systemic disease, and in an adult
    only as his cytopenia worsened — which is a diagnostic trap rather than a
    mechanistic difference.
  cell_types:
  - preferred_term: epithelial cell
    term:
      id: CL:0000066
      label: epithelial cell
  downstream:
  - target: Nail dystrophy
    causal_link_type: DIRECT
  - target: Oral leukoplakia
    causal_link_type: DIRECT
  - target: Reticulated skin pigmentation
    causal_link_type: DIRECT
  - target: Premature graying of hair
    causal_link_type: DIRECT
  evidence:
  - reference: PMID:37440454
    reference_title: "Novel pathological variants of NHP2 affect N-terminal domain flexibility, protein stability, H/ACA Ribonucleoprotein (RNP) complex formation and telomerase activity."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Further clinical investigation revealed nail dystrophies, gray hair, tooth
      loss and oral leukoplakia with a bone marrow cellularity between 30 and 40%
    explanation: >-
      The mucocutaneous features appearing alongside declining marrow
      cellularity in a genetically confirmed NHP2 patient.
- name: Clonal Evolution in the Failing Marrow
  biological_scale: CELLULAR
  description: >-
    A marrow under replicative stress with unprotected chromosome ends selects
    for clones that tolerate it, and the telomere biology disorders carry a
    recognised risk of myelodysplastic syndrome and acute myeloid leukaemia. In
    NHP2 specifically this is a single reported patient with low-risk
    myelodysplastic syndrome, so the risk is asserted here at the strength of one
    case plus the disorder-family literature, not as a quantified
    genotype-specific figure. The gastric carcinoma in that same patient is not
    placed on this node: the reporting paper keeps the two apart, ascribing the
    myelodysplasia to clonal haematopoiesis from telomere shortening while
    leaving the tumour's etiology unknown.
  cell_types:
  - preferred_term: hematopoietic stem cell
    term:
      id: CL:0000037
      label: hematopoietic stem cell
  downstream:
  - target: Myelodysplasia
    causal_link_type: DIRECT
  evidence:
  - reference: PMID:37440454
    reference_title: "Novel pathological variants of NHP2 affect N-terminal domain flexibility, protein stability, H/ACA Ribonucleoprotein (RNP) complex formation and telomerase activity."
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: BACKGROUND
    snippet: >-
      Furthermore, TBDs patients show an increased predisposition to
      hematological malignancies and, more rarely, solid tumors
    explanation: >-
      The disorder-family malignancy risk, quoted from the citing paper's review
      of prior work rather than from its own data.
  - reference: PMID:20301779
    reference_title: Dyskeratosis Congenita and Related Telomere Biology Disorders.
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      People with DC/TBD are at increased risk for progressive bone marrow
      failure (BMF), myelodysplastic syndrome or acute myelogenous leukemia,
      solid tumors (usually squamous cell carcinoma of the head/neck or
      anogenital cancer), and pulmonary fibrosis.
    explanation: >-
      The GeneReviews statement of malignancy risk across the telomere biology
      disorders, which is the basis for surveillance on genotype.
- name: Extra-Hematopoietic Tissue Dysfunction
  biological_scale: ORGANISM
  description: >-
    Liver, brain and lens involvement in the reported NHP2 patients sits outside
    what marrow-facing telomere attrition explains on its own. Whether these
    follow from telomere shortening in those tissues, from the rRNA biogenesis
    defect, or from both is unresolved.
  downstream:
  - target: Cirrhosis
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
  - target: Intellectual disability
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
  - target: Global developmental delay
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
  - target: Cataract
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
  - target: Cerebral calcification
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
  evidence:
  - reference: PMID:40352450
    reference_title: "Siblings with a Homozygous Variant in the NHP2 Gene: A Case Report and Review of Literature."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      she had an 18-year-old brother with cataracts, intellectual disability,
      liver cirrhosis, pancytopenia, and hypersplenism
    explanation: >-
      The extra-haematopoietic constellation in a homozygous NHP2 patient, which
      this node collects.
phenotypes:
- category: Hematologic
  name: Short telomere length
  description: >-
    Leukocyte telomeres short for age are the diagnostic hallmark shared across
    the telomere biology disorders and were present in the NHP2 patients from the
    founding report onwards.
  phenotype_term:
    preferred_term: Short telomere length
    term:
      id: HP:0031413
      label: Short telomere length
  frequency: VERY_FREQUENT
  evidence:
  - reference: PMID:18523010
    reference_title: Mutations in the telomerase component NHP2 cause the premature ageing syndrome dyskeratosis congenita.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Patients with NHP2 mutations, in common with patients bearing dyskerin and
      NOP10 mutations had short telomeres and low TERC levels.
    explanation: Short telomeres measured in the founding NHP2 patients.
- category: Hematologic
  name: Bone marrow failure
  description: >-
    Progressive marrow failure is the dominant threat to life. In the adult
    compound heterozygote marrow cellularity fell from 30-40% to 10-30% over
    eight months with dysplastic erythro- and megakaryopoiesis.
  phenotype_term:
    preferred_term: Bone marrow hypocellularity
    term:
      id: HP:0005528
      label: Bone marrow hypocellularity
  frequency: FREQUENT
  evidence:
  - reference: CGGV:assertion_a8fa9dcb-1cc6-43a2-8f86-e6cea0e6fce2-2025-08-01T160000.000Z
    reference_title: NHP2 / dyskeratosis congenita, autosomal recessive 2 (Limited)
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      nail dystrophy, bone marrow failure, intellectual disability, and short
      telomeres
    explanation: >-
      Marrow failure in ClinGen's list of what biallelic NHP2 carriers present
      with.
  - reference: PMID:37440454
    reference_title: "Novel pathological variants of NHP2 affect N-terminal domain flexibility, protein stability, H/ACA Ribonucleoprotein (RNP) complex formation and telomerase activity."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      which decreased to 10–30% in the following 8 months, with normal karyotype
      but erythro- and megakaryopoiesis dysplasia, suggesting TBDs
    explanation: The rate of marrow decline in one NHP2 patient, with the dysplastic changes.
- category: Hematologic
  name: Pancytopenia
  description: >-
    Both siblings in the consanguineous family were pancytopenic, the index
    patient by ten years of age.
  phenotype_term:
    preferred_term: Pancytopenia
    term:
      id: HP:0001876
      label: Pancytopenia
  frequency: FREQUENT
  evidence:
  - reference: PMID:40352450
    reference_title: "Siblings with a Homozygous Variant in the NHP2 Gene: A Case Report and Review of Literature."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      additional findings that included intellectual disability, liver disease,
      pancytopenia, nail dystrophy
    explanation: Pancytopenia in the index child after eight years of follow-up.
- category: Dermatologic
  name: Nail dystrophy
  description: >-
    One of the classic triad. In this genotype it appears late — after eight
    years of follow-up in a child who presented at two, and in an adult only as
    his cytopenia worsened.
  phenotype_term:
    preferred_term: Nail dystrophy
    term:
      id: HP:0008404
      label: Nail dystrophy
  frequency: FREQUENT
  evidence:
  - reference: CGGV:assertion_a8fa9dcb-1cc6-43a2-8f86-e6cea0e6fce2-2025-08-01T160000.000Z
    reference_title: NHP2 / dyskeratosis congenita, autosomal recessive 2 (Limited)
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      oral leukoplakia, reticular skin pigmentation, nail dystrophy
    explanation: ClinGen's phenotype list for biallelic NHP2 carriers.
- category: Dermatologic
  name: Oral leukoplakia
  description: >-
    One of the classic triad; reported in the adult compound heterozygote and in
    the older sibling of the consanguineous pair, in both cases years after the
    systemic disease began.
  phenotype_term:
    preferred_term: Oral leukoplakia
    term:
      id: HP:0002745
      label: Oral leukoplakia
  frequency: FREQUENT
  evidence:
  - reference: PMID:37440454
    reference_title: "Novel pathological variants of NHP2 affect N-terminal domain flexibility, protein stability, H/ACA Ribonucleoprotein (RNP) complex formation and telomerase activity."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Further clinical investigation revealed nail dystrophies, gray hair, tooth
      loss and oral leukoplakia
    explanation: The mucocutaneous features in a confirmed NHP2 patient.
- category: Dermatologic
  name: Reticulated skin pigmentation
  description: >-
    The third element of the triad. In the eighteen-year-old brother it appeared
    on the neck only in the two years before the family was reported.
  phenotype_term:
    preferred_term: Reticulated skin pigmentation
    term:
      id: HP:0007427
      label: Reticulated skin pigmentation
  frequency: FREQUENT
  evidence:
  - reference: PMID:40352450
    reference_title: "Siblings with a Homozygous Variant in the NHP2 Gene: A Case Report and Review of Literature."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      her brother developed nail dystrophy, oral leucoplakia, graying hair, and
      reticular pigmentation on his neck
    explanation: The triad completing itself in late adolescence in an NHP2 homozygote.
- category: Dermatologic
  name: Premature graying of hair
  description: >-
    Reported in both the adult compound heterozygote and the adolescent
    homozygote, consistent with the premature-ageing framing of the disorder.
  phenotype_term:
    preferred_term: Premature graying of hair
    term:
      id: HP:0002216
      label: Premature graying of hair
  frequency: OCCASIONAL
  evidence:
  - reference: PMID:37440454
    reference_title: "Novel pathological variants of NHP2 affect N-terminal domain flexibility, protein stability, H/ACA Ribonucleoprotein (RNP) complex formation and telomerase activity."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      revealed nail dystrophies, gray hair, tooth loss and oral leukoplakia
    explanation: Grey hair recorded in an NHP2 patient at 45.
- category: Neurologic
  name: Intellectual disability
  description: >-
    Present in both siblings of the consanguineous family and listed by ClinGen
    among the features of biallelic NHP2 disease. It is not a general feature of
    dyskeratosis congenita, in which most individuals have normal neurologic
    function, so its presence here is informative.
  phenotype_term:
    preferred_term: Intellectual disability
    term:
      id: HP:0001249
      label: Intellectual disability
  frequency: FREQUENT
  evidence:
  - reference: CGGV:assertion_a8fa9dcb-1cc6-43a2-8f86-e6cea0e6fce2-2025-08-01T160000.000Z
    reference_title: NHP2 / dyskeratosis congenita, autosomal recessive 2 (Limited)
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      bone marrow failure, intellectual disability, and short telomeres
    explanation: Intellectual disability in ClinGen's phenotype list for this entity.
  - reference: PMID:20301779
    reference_title: Dyskeratosis Congenita and Related Telomere Biology Disorders.
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      Although most persons with DC/TBD have normal psychomotor development and
      normal neurologic function, significant developmental delay is present in
      both forms
    explanation: >-
      The contrast that makes the neurological involvement in NHP2 patients worth
      recording rather than assuming.
- category: Neurologic
  name: Global developmental delay
  description: >-
    The index child presented at two years with developmental delay and inability
    to walk, before any haematological or mucocutaneous sign.
  phenotype_term:
    preferred_term: Global developmental delay
    term:
      id: HP:0001263
      label: Global developmental delay
    onset:
      onset_category: INFANTILE
  evidence:
  - reference: PMID:40352450
    reference_title: "Siblings with a Homozygous Variant in the NHP2 Gene: A Case Report and Review of Literature."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      complaints of inability to walk and decreased vision, as well as
      developmental delay and cataracts
    explanation: The presenting complaint at two years of age.
- category: Ophthalmologic
  name: Cataract
  description: >-
    Cataracts were present in both siblings — in the index patient at two years,
    causing the decreased vision that brought her to attention. Cataract is not
    part of the classic dyskeratosis congenita eye picture, which is an
    ocular-surface and lid problem.
  phenotype_term:
    preferred_term: Cataract
    term:
      id: HP:0000518
      label: Cataract
    onset:
      onset_category: CHILDHOOD
  evidence:
  - reference: PMID:40352450
    reference_title: "Siblings with a Homozygous Variant in the NHP2 Gene: A Case Report and Review of Literature."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      she had an 18-year-old brother with cataracts, intellectual disability,
      liver cirrhosis, pancytopenia, and hypersplenism
    explanation: Cataracts in both affected siblings of the homozygous family.
- category: Neurologic
  name: Cerebral calcification
  description: >-
    Multiple intracranial foci of calcification were found on follow-up imaging
    of the index child, having begun as hypointense foci in the basal ganglia,
    thalamus and parietal white matter at presentation.
  phenotype_term:
    preferred_term: Cerebral calcification
    term:
      id: HP:0002514
      label: Cerebral calcification
  frequency: OCCASIONAL
  evidence:
  - reference: PMID:40352450
    reference_title: "Siblings with a Homozygous Variant in the NHP2 Gene: A Case Report and Review of Literature."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      nail dystrophy, multiple foci of calcification on magnetic resonance
      imaging of the brain
    explanation: The imaging finding on follow-up of the index patient.
- category: Gastrointestinal
  name: Cirrhosis
  description: >-
    Liver involvement ran from cirrhosis with hypersplenism in the older sibling
    to liver disease identified on follow-up in the younger. Liver disease is a
    recognised feature of the telomere biology disorders generally.
  phenotype_term:
    preferred_term: Cirrhosis
    term:
      id: HP:0001394
      label: Cirrhosis
  frequency: OCCASIONAL
  evidence:
  - reference: PMID:40352450
    reference_title: "Siblings with a Homozygous Variant in the NHP2 Gene: A Case Report and Review of Literature."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      an 18-year-old brother with cataracts, intellectual disability, liver
      cirrhosis, pancytopenia, and hypersplenism
    explanation: Cirrhosis in the older affected sibling.
  sequelae:
  - target: Hypersplenism
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    description: >-
      Cirrhosis and hypersplenism were reported together in the older sibling.
      The intervening step, portal hypertension with splenic congestion, was not
      measured in that report and is omitted from this graph.
- category: Hematologic
  name: Hypersplenism
  description: >-
    Hypersplenism was present in the older affected sibling alongside cirrhosis
    and pancytopenia, so splenic sequestration is a plausible contributor to his
    cytopenias in addition to the marrow failure the telomere defect produces.
    The two cannot be separated from the published description.
  phenotype_term:
    preferred_term: Hypersplenism
    term:
      id: HP:0001971
      label: Hypersplenism
  frequency: OCCASIONAL
  evidence:
  - reference: PMID:40352450
    reference_title: "Siblings with a Homozygous Variant in the NHP2 Gene: A Case Report and Review of Literature."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      an 18-year-old brother with cataracts, intellectual disability, liver
      cirrhosis, pancytopenia, and hypersplenism
    explanation: Hypersplenism in the older affected sibling.
- category: Hematologic
  name: Myelodysplasia
  description: >-
    Low-risk myelodysplastic syndrome with a normal karyotype was the presenting
    haematological diagnosis in the adult compound heterozygote, seven years
    before his cytopenia worsened and the telomere biology disorder was
    recognised.
  phenotype_term:
    preferred_term: Myelodysplasia
    term:
      id: HP:0002863
      label: Myelodysplasia
  frequency: OCCASIONAL
  evidence:
  - reference: PMID:37440454
    reference_title: "Novel pathological variants of NHP2 affect N-terminal domain flexibility, protein stability, H/ACA Ribonucleoprotein (RNP) complex formation and telomerase activity."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      diagnosed at age 38 with gastric cancer and low-risk MDS, with normal
      karyotype (46,XY[20])
    explanation: Myelodysplastic syndrome in a genetically confirmed NHP2 patient.
- category: Neoplastic
  name: Gastric carcinoma
  description: >-
    The only solid tumour so far reported in a genetically confirmed NHP2
    patient, diagnosed at 38 alongside myelodysplastic syndrome and resected.
    One case does not establish an NHP2-specific gastric cancer risk, and no
    NHP2-specific cancer incidence has been published; the surveillance this
    entry carries rests on the disorder-family risk rather than on this report.
  phenotype_term:
    preferred_term: Stomach cancer
    term:
      id: HP:0012126
      label: Stomach cancer
  frequency: OCCASIONAL
  evidence:
  - reference: PMID:37440454
    reference_title: "Novel pathological variants of NHP2 affect N-terminal domain flexibility, protein stability, H/ACA Ribonucleoprotein (RNP) complex formation and telomerase activity."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The index patient with no family history of MDS was diagnosed at age 38
      with gastric cancer and low-risk MDS
    explanation: >-
      Names the gastric cancer and the age at diagnosis in the index NHP2
      patient of that report.
genetic:
- name: NHP2
  gene_term:
    preferred_term: NHP2
    term:
      id: hgnc:14377
      label: NHP2
  relationship_type: CAUSATIVE
  notes: >-
    NHP2 (5q35.3), formerly NOLA2, encodes a small basic protein of the box H/ACA
    ribonucleoprotein. It has no catalytic activity; its contribution is
    structural, docking through NOP10 and contacting the telomerase RNA directly
    in the resolved holoenzyme structures. ClinGen's Interstitial Lung Disease
    expert panel classifies the NHP2 - dyskeratosis congenita autosomal recessive
    2 relationship as Limited, reaffirmed in August 2025 after the additional
    case and functional data of PMID:37440454 and PMID:31985013 did not change
    it. Limited is a statement about the quantity of evidence, not a doubt about
    the mechanism, and it is the honest headline for a gene with four curated
    probands.
  variants:
  - name: c.376G>A (p.Val126Met) in trans with c.460T>A (p.Ter154Arg)
    description: >-
      Compound heterozygous genotype of a long-followed patient. V126M is one of
      the two alleles shown to impair NOP10 association; the second is a
      stop-loss extension.
  - name: c.415T>C (p.Tyr139His), homozygous
    description: >-
      Homozygous genotype in two siblings of a consanguineous family, with both
      parents heterozygous. Y139H is the other allele shown to impair NOP10
      association and H/ACA pre-ribonucleoprotein assembly.
  - name: p.Ala39Thr in trans with p.Thr44Met
    description: >-
      Compound heterozygous genotype of an adult with myelodysplastic syndrome
      and gastric cancer. Both variants sit in the N-terminal region and are
      mis-incorporated into the H/ACA complex, then degraded by the proteasome.
  evidence:
  - reference: PMID:18523010
    reference_title: Mutations in the telomerase component NHP2 cause the premature ageing syndrome dyskeratosis congenita.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      We have identified previously uncharacterized NHP2 mutations that can cause
      autosomal recessive dyskeratosis congenita but have not found any GAR1
      mutations.
    explanation: >-
      The gene-disease claim as first made, with the negative result for the
      fourth core protein in the same sentence.
  - reference: PMID:30472699
    reference_title: "Long-Term Follow-Up of a Case with Dyskeratosis Congenita Caused by NHP2-V126M/X154R Mutation: Genotype-Phenotype Association."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      a patient with NHP2 gene mutation (compound heterozygote for the NHP2
      mutations c.376G>A/c.460T>A; amino acid substitutions: p.Val126Met and
      p.X154Arg) that occurred as a compound heterozygous state
    explanation: The compound heterozygous genotype of the long-followed patient.
  - reference: PMID:40352450
    reference_title: "Siblings with a Homozygous Variant in the NHP2 Gene: A Case Report and Review of Literature."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Genome sequencing revealed a c.415T>C (p.Tyr139His) disease-causing variant
      in the NHP2 gene
    explanation: The homozygous allele in the consanguineous sibship.
  - reference: CGGV:assertion_a8fa9dcb-1cc6-43a2-8f86-e6cea0e6fce2-2025-08-01T160000.000Z
    reference_title: NHP2 / dyskeratosis congenita, autosomal recessive 2 (Limited)
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      | NHP2 | HGNC:14377 | dyskeratosis congenita, autosomal recessive 2 |
      MONDO:0013519 | AR | Limited | SOP11 | Interstitial Lung Disease Gene
      Curation Expert Panel | 2025-08-01T16:00:00.000Z |
    explanation: >-
      The ClinGen gene-disease validity row, which is also what ties this gene to
      this MONDO identifier.
biochemical:
- name: Telomerase RNA component (TERC) level in peripheral blood
  notes: >-
    Low TERC in peripheral blood was the measurement that placed NHP2 in the
    telomerase pathway in humans. It is a research assay; the clinical test is
    leukocyte telomere length.
  evidence:
  - reference: PMID:18523010
    reference_title: Mutations in the telomerase component NHP2 cause the premature ageing syndrome dyskeratosis congenita.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      have all been shown to have low levels of telomerase RNA in their
      peripheral blood, providing direct evidence of their role in telomere
      maintenance in humans
    explanation: The patient-level TERC measurement.
- name: Leukocyte telomere length by flow-FISH
  notes: >-
    Multicolour flow-FISH on lymphocyte subsets is the diagnostic assay across
    the telomere biology disorders, with results below the first percentile for
    age supporting the diagnosis. In a child presenting with developmental delay,
    cataracts and cytopenias it is the test that reframes the differential.
  evidence:
  - reference: PMID:20301779
    reference_title: Dyskeratosis Congenita and Related Telomere Biology Disorders.
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      A majority of individuals with DC/TBD have abnormally short telomeres for
      their age, as determined by multicolor flow cytometry fluorescence in situ
      hybridization (flow-FISH) on lymphocyte subsets.
    explanation: The GeneReviews diagnostic-testing statement.
treatments:
- name: Hematopoietic cell transplantation
  description: >-
    The only curative option for marrow failure and leukaemia in the telomere
    biology disorders. The toxicity caveat is not generic: the same telomere
    defect is present in every tissue the conditioning regimen exposes. The one
    reported NHP2 patient to be transplanted rejected the first graft and died of
    Epstein-Barr virus infection after the second.
  therapeutic_modality: CELL_THERAPY
  treatment_term:
    preferred_term: Hematopoietic Cell Transplantation
    term:
      id: NCIT:C15431
      label: Hematopoietic Cell Transplantation
  target_mechanisms:
  - target: Hematopoietic Stem Cell Exhaustion
    description: >-
      Replaces the exhausted stem cell compartment. It does nothing for the
      hepatic, neurological, ocular or solid-tumour risk arising in tissues the
      graft does not reach.
  evidence:
  - reference: PMID:20301779
    reference_title: Dyskeratosis Congenita and Related Telomere Biology Disorders.
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      Hematopoietic cell transplantation (HCT) is the only curative treatment for
      BMF and leukemia, but long-term outcome has historically been poor due to
      treatment toxicity; if a suitable donor is not available, androgen therapy
      may be considered for BMF.
    explanation: The GeneReviews management statement with its toxicity caveat.
  - reference: PMID:37440454
    reference_title: "Novel pathological variants of NHP2 affect N-terminal domain flexibility, protein stability, H/ACA Ribonucleoprotein (RNP) complex formation and telomerase activity."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The patient underwent allogeneic bone marrow transplantations but rejected
      the graft and, after a second transplantation, unfortunately died of
      Epstein–Barr virus infection.
    explanation: The transplant outcome in the only reported NHP2 recipient.
- name: Androgen therapy
  description: >-
    Considered for marrow failure when no suitable donor is available. It
    requires monitoring of blood count, liver function, liver ultrasound and
    endocrine status — the liver items matter more than usual in a disorder that
    carries its own hepatic risk. Androgens must not be combined with granulocyte
    colony-stimulating factor.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Androgen Therapy
    term:
      id: NCIT:C15482
      label: Androgen Therapy
  target_mechanisms:
  - target: Hematopoietic Stem Cell Exhaustion
    description: >-
      Improves counts in marrow failure. No NHP2 patient has been reported on
      androgen therapy, so this is genotype-level management inherited from the
      disorder family.
  evidence:
  - reference: PMID:20301779
    reference_title: Dyskeratosis Congenita and Related Telomere Biology Disorders.
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      the combination of androgens and granulocyte colony-stimulating factor in
      treatment of BMF (has been associated with splenic rupture)
    explanation: The drug-safety warning from the GeneReviews avoidance list.
  - reference: PMID:20301779
    reference_title: Dyskeratosis Congenita and Related Telomere Biology Disorders.
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      if a suitable donor is not available, androgen therapy may be considered
      for BMF
    explanation: >-
      The GeneReviews indication for androgen therapy, which places it as the
      option when transplantation is not available.
- name: Marrow failure surveillance
  description: >-
    Complete blood count annually if normal and more often if abnormal, with
    annual bone marrow aspirate and biopsy. In this genotype the schedule should
    start at diagnosis and not wait for the mucocutaneous triad, which the
    reported patients developed years after their cytopenias.
  therapeutic_modality: OTHER
  treatment_term:
    preferred_term: Supportive Care
    term:
      id: NCIT:C15747
      label: Supportive Care
  evidence:
  - reference: PMID:20301779
    reference_title: Dyskeratosis Congenita and Related Telomere Biology Disorders.
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      For BMF: complete blood count (CBC) annually if normal and more often if
      abnormal; annual bone marrow aspirate and biopsy.
    explanation: The GeneReviews marrow surveillance schedule.
- name: Cancer surveillance
  description: >-
    Monthly self-examination for oral, head and neck cancer, annual screening by
    an otolaryngologist and a dermatologist, and annual gynaecological
    examination, with six-monthly dental review and avoidance of smoking and
    excessive sun exposure. This is the reason cancer predisposition is carried on
    this entry rather than deferred to the parent: surveillance is recommended on
    the basis of genotype, and a family given an NHP2 result needs the schedule
    whether or not a malignancy has yet been reported in that genotype.
  therapeutic_modality: OTHER
  treatment_term:
    preferred_term: Supportive Care
    term:
      id: NCIT:C15747
      label: Supportive Care
  evidence:
  - reference: PMID:20301779
    reference_title: Dyskeratosis Congenita and Related Telomere Biology Disorders.
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      For cancer risk: monthly self-examination for oral, head, and neck cancer;
      annual cancer screening by an otolaryngologist and dermatologist; annual
      gynecologic examination.
    explanation: The GeneReviews cancer surveillance schedule.
- name: Pulmonary function surveillance
  description: >-
    Annual pulmonary function testing from diagnosis or from about age eight,
    when a child can perform the test. Worth noting that interstitial lung
    disease has not been observed in the biallelic NHP2 entity, so this is
    disorder-family surveillance rather than a genotype-specific expectation.
  therapeutic_modality: OTHER
  treatment_term:
    preferred_term: Supportive Care
    term:
      id: NCIT:C15747
      label: Supportive Care
  evidence:
  - reference: PMID:20301779
    reference_title: Dyskeratosis Congenita and Related Telomere Biology Disorders.
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      For pulmonary fibrosis: annual pulmonary function tests starting either at
      diagnosis or when the individual can perform the test (often age ~8 years)
    explanation: The GeneReviews pulmonary surveillance schedule.
  - reference: CGGV:assertion_a8fa9dcb-1cc6-43a2-8f86-e6cea0e6fce2-2025-08-01T160000.000Z
    reference_title: NHP2 / dyskeratosis congenita, autosomal recessive 2 (Limited)
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      but to date ILD has not been observed for this gene-disease entity
    explanation: >-
      The genotype-specific qualification on the surveillance recommendation
      above.
- name: Genetic counseling
  description: >-
    Parents of an affected child are obligate carriers with a 25% recurrence risk
    in each pregnancy. Relatives being considered as transplant donors must be
    tested — for the familial variants where known, or by telomere length — before
    donating, because a heterozygous sibling donor may have a telomere defect of
    their own. Family members should not donate blood if transplantation is
    contemplated.
  therapeutic_modality: OTHER
  treatment_term:
    preferred_term: Genetic Counseling
    term:
      id: NCIT:C15240
      label: Genetic Counseling
  evidence:
  - reference: PMID:20301779
    reference_title: Dyskeratosis Congenita and Related Telomere Biology Disorders.
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      If a relative has signs or symptoms suggestive of DC/TBD or is being
      evaluated as a potential HCT donor, telomere length testing – or, if the
      pathogenic variant(s) in the family are known, molecular genetic testing –
      is warranted.
    explanation: The GeneReviews evaluation-of-relatives-at-risk statement.
discussions:
- discussion_id: gap_dkcb2_rrna_versus_telomere
  kind: KNOWLEDGE_GAP
  status: OPEN
  prompt: >-
    Which of the extra-haematopoietic features of DKCB2 follow from telomere
    attrition, and which from the ribosomal RNA biogenesis defect?
  attaches_to:
  - "pathophysiology#Ribosomal RNA Biogenesis Impairment"
  - "pathophysiology#Extra-Hematopoietic Tissue Dysfunction"
  rationale: >-
    Intellectual disability, infantile cataract and intracranial calcification
    are not what a pure short-telomere phenotype predicts, and most people with
    dyskeratosis congenita have normal neurological function. NHP2 deficiency
    demonstrably impairs rRNA biogenesis, which makes a ribosomopathy-like arm
    the obvious candidate, and the authors of the H/ACA assembly study argued in
    exactly that direction — that some of the disorders in dyskeratosis congenita
    may come from alteration of H/ACA ribonucleoproteins generally rather than
    from the telomerase arm alone. Nothing separates the two: no NHP2 patient has
    had ribosome biogenesis and telomere length measured against the presence or
    absence of the neurological features, and with four curated probands the
    cohort to do it in does not exist. The distinction is not academic. A
    telomere-directed therapy that restored TERC would be expected to help the
    marrow and leave a ribosomal arm untouched.
  proposed_experiments:
  - experiment_id: exp_dkcb2_rrna_in_patient_cells
    name: rRNA processing profiling across NHP2 genotypes
    description: >-
      Measure pre-rRNA processing intermediates and telomere length in primary
      cells from each reported NHP2 genotype, and test whether the magnitude of
      the rRNA defect tracks the neurological and ocular features rather than the
      haematological ones.
    would_support:
    - "pathophysiology#Ribosomal RNA Biogenesis Impairment"
- discussion_id: gap_dkcb2_cancer_risk_unquantified
  kind: KNOWLEDGE_GAP
  status: OPEN
  prompt: >-
    What is the cancer risk in biallelic NHP2 disease, and does it differ from
    the telomere biology disorders generally?
  attaches_to:
  - "pathophysiology#Clonal Evolution in the Failing Marrow"
  - "phenotypes#Gastric carcinoma"
  rationale: >-
    One myelodysplastic syndrome and one gastric carcinoma have been reported in
    a single NHP2 patient. That is enough to say the risk is not obviously absent
    and nowhere near enough to quantify it, or to say whether the tumour spectrum
    differs from the head-and-neck and anogenital squamous cancers that dominate
    the disorder family. Cohort studies that produce cumulative cancer incidence
    for inherited bone marrow failure syndromes are powered on the common
    genotypes; four probands will not appear in them separately. The practical
    consequence is that surveillance in DKCB2 has to be prescribed on the
    disorder-family schedule, which is what this entry does, and that a family
    asking for a number cannot be given one.
  proposed_experiments:
  - experiment_id: exp_dkcb2_registry_pooling
    name: Pooled telomere biology disorder registry analysis by gene
    description: >-
      Pool the international inherited bone marrow failure and telomere biology
      registries and report cancer incidence stratified by causal gene, so that
      the rare H/ACA-complex genotypes are reported as a group with their own
      confidence intervals rather than absorbed into an all-genotype figure.
- discussion_id: gap_dkcb2_heterozygote_risk
  kind: KNOWLEDGE_GAP
  status: OPEN
  prompt: >-
    Do heterozygous NHP2 carriers — including the parents of an affected child —
    have a telomere-related disease risk of their own?
  attaches_to:
  - "genetic#NHP2"
  rationale: >-
    Heterozygous NHP2 variants have been reported in adults with pulmonary
    fibrosis, and in one of those patients a somatic TERT promoter mutation
    appeared to give a subset of blood cells a selective advantage, which is the
    behaviour of a compartment under telomere stress rather than of a neutral
    carrier state. Against that, ClinGen excluded the heterozygous cases from its
    curation on the grounds of population frequency and insufficient genotyping
    detail. Both readings are defensible on the published evidence. It matters at
    the point of counselling — obligate-carrier parents of a DKCB2 child would be
    told something different under each — and again when a parent or sibling is
    considered as a transplant donor.
  proposed_experiments:
  - experiment_id: exp_dkcb2_carrier_telomere_lengths
    name: Telomere length and pulmonary phenotyping of obligate NHP2 carriers
    description: >-
      Measure leukocyte telomere length and pulmonary function in the obligate
      heterozygous parents of reported biallelic NHP2 patients, against
      age-matched controls, and follow them prospectively for interstitial lung
      disease.
    would_support:
    - "genetic#NHP2"
notes: >-
  Scope and lump/split. This entry is biallelic NHP2 telomere biology disease.
  It is a standalone file rather than content added to Dyskeratosis_Congenita,
  following the precedent already set on main by
  Dyskeratosis_Congenita_Autosomal_Recessive_6 (PARN) and
  Dyskeratosis_Congenita_Autosomal_Recessive_8. Those two entries and the parent
  divide the material in a particular way and this one keeps to it: the parent
  carries the disorder-family pathograph — impaired telomere maintenance,
  critically short telomeres, stem cell exhaustion — plus a short gene-keyed
  has_subtypes row for each causal gene, including NHP2, and the numbered entries
  carry the gene-specific upstream mechanism that the family-level chain cannot
  express. Here that is the H/ACA ribonucleoprotein assembly step: NHP2 reaches
  the telomere only because the telomerase RNA happens to be an H/ACA RNA, which
  is also why the same lesion hits ribosomal RNA. The parent's NHP2 has_subtypes
  row is deliberately left in place, exactly as the parent's PARN row was left in
  place when the PARN entry was written; it is a pointer, not a duplicate.

  Cancer predisposition is carried here, not deferred to the parent. Two reasons.
  A genetically confirmed NHP2 patient has been reported with myelodysplastic
  syndrome and gastric carcinoma, so the claim is not purely inherited from the
  disorder family; and the surveillance that follows is prescribed on genotype,
  which means the family holding an NHP2 result needs it on the page that
  describes their result. What is deliberately not here is a number. No
  NHP2-specific cancer incidence, cumulative risk or standardised incidence ratio
  has been published, the whole curated literature is four probands, and a figure
  borrowed from an all-genotype dyskeratosis congenita cohort would be presented
  as something it is not. The gap is recorded as a discussion rather than filled.

  Relationship to the marrow failure records. Bone_Marrow_Failure_IEIs already
  accounts for NHP2 in its rationale, as one of the telomerase-ribonucleoprotein
  genes of IUIS Table 9, and does not list it as missing, so no grouping change
  follows from this entry. Inherited_Aplastic_Anemia is a Disease entry rather
  than a grouping and is not a member list, so there is nothing there to update
  either.

  Module conformance. Two nodes declare conforms_to against telomere_attrition,
  at the attrition and the senescence steps. The upstream nodes deliberately do
  not: H/ACA assembly failure and rRNA biogenesis impairment are not steps in
  that module and conforming them would assert a correspondence that does not
  exist.

  What is deliberately absent. No datasets: block — searching NHP2 retrieves the
  ribosome-biogenesis and cancer-expression literature far more readily than the
  handful of telomere patients, and no DKCB2-specific dataset was identified. No
  clinical_trials: block — no interventional trial keyed to biallelic NHP2
  disease was found, and listing a general dyskeratosis congenita trial would
  misattribute it. No animal_models: block — no NHP2 animal model of the human
  biallelic disease has been reported; the functional work is in human cells. No
  environmental: block. Frequency values are given only where more than one
  patient supports them, which is why several features that are certainly real in
  the reported patients carry no frequency at all.

  Evidence provenance. Several quoted items carry quote_role: BACKGROUND or
  REVIEW_SYNTHESIS. With four curated probands, most general statements about
  this disease appear in the introductions of molecular papers or in a
  GeneReviews chapter about the disorder family rather than in a cohort study of
  DKCB2. Recording where in the citing document each quote sits is what keeps
  those claims honest.

  Two reports were read and deliberately not cited. PMID:36943377 (idiopathic
  non-cirrhotic portal hypertension with a rare NHP2 variant) and PMID:40073202
  (expanding the clinical spectrum of NHP2-related dyskeratosis congenita) are
  both directly on topic, and neither has any retrievable text beyond its title —
  the publishers release no abstract. Quoting a title is not quoting a finding,
  so the features they report are absent from this entry. A curator with
  institutional access to either should expect to add phenotypes.

  Features recorded only in OMIM's clinical synopsis. The homozygous p.Tyr139His
  proband of the founding report is described in secondary sources as having
  testicular atrophy, growth retardation, recurrent opportunistic infection and
  intracranial calcification, and those features populate the Monarch phenotype
  list for this MONDO term. The Vulliamy abstract does not enumerate them and the
  full text was not retrievable here, so they are not curated as phenotypes:
  every phenotype in this entry is quoted from a source in the reference cache.
  Cerebral calcification is present because the 2025 sibling report states it
  independently. Anyone with access to the PNAS full text should expect to add
  the remainder.

  GeneReviews. PMID:20301779, Dyskeratosis Congenita and Related Telomere Biology
  Disorders, is the baseline chapter and is tagged in references:. It covers the
  disorder family; there is no NHP2-specific chapter, exactly as for the PARN and
  AR8 entries. Its clinical-characteristics list was cross-checked against the
  phenotypes here. Features it names that no NHP2 patient has been reported to
  have — taurodontism, gastrointestinal telangiectasia, the ocular-surface and
  lid findings, avascular necrosis, pulmonary fibrosis, squamous cell carcinoma —
  are not curated as phenotypes of this entry. The surveillance those features
  drive is curated under treatments, where it belongs, because surveillance is
  recommended on genotype rather than on manifestation.
references:
- reference: PMID:20301779
  title: Dyskeratosis Congenita and Related Telomere Biology Disorders.
  tags:
  - GeneReviews
- reference: PMID:18523010
  title: Mutations in the telomerase component NHP2 cause the premature ageing syndrome dyskeratosis congenita.
- reference: PMID:20008900
  title: "Effects of dyskeratosis congenita mutations in dyskerin, NHP2 and NOP10 on assembly of H/ACA pre-RNPs."
- reference: PMID:30472699
  title: "Long-Term Follow-Up of a Case with Dyskeratosis Congenita Caused by NHP2-V126M/X154R Mutation: Genotype-Phenotype Association."
- reference: PMID:31985013
  title: NHP2 deficiency impairs rRNA biogenesis and causes pulmonary fibrosis and Høyeraal-Hreidarsson syndrome.
- reference: PMID:37440454
  title: "Novel pathological variants of NHP2 affect N-terminal domain flexibility, protein stability, H/ACA Ribonucleoprotein (RNP) complex formation and telomerase activity."
- reference: PMID:40352450
  title: "Siblings with a Homozygous Variant in the NHP2 Gene: A Case Report and Review of Literature."
- reference: CGGV:assertion_a8fa9dcb-1cc6-43a2-8f86-e6cea0e6fce2-2025-08-01T160000.000Z
  title: NHP2 / dyskeratosis congenita, autosomal recessive 2 (Limited)
datasets: []
📚

References & Deep Research

References

8
PMID:20301779
Dyskeratosis Congenita and Related Telomere Biology Disorders.
No top-level findings curated for this source.
PMID:18523010
Mutations in the telomerase component NHP2 cause the premature ageing syndrome dyskeratosis congenita.
No top-level findings curated for this source.
PMID:20008900
Effects of dyskeratosis congenita mutations in dyskerin, NHP2 and NOP10 on assembly of H/ACA pre-RNPs.
No top-level findings curated for this source.
PMID:30472699
Long-Term Follow-Up of a Case with Dyskeratosis Congenita Caused by NHP2-V126M/X154R Mutation: Genotype-Phenotype Association.
No top-level findings curated for this source.
PMID:31985013
NHP2 deficiency impairs rRNA biogenesis and causes pulmonary fibrosis and Høyeraal-Hreidarsson syndrome.
No top-level findings curated for this source.
PMID:37440454
Novel pathological variants of NHP2 affect N-terminal domain flexibility, protein stability, H/ACA Ribonucleoprotein (RNP) complex formation and telomerase activity.
No top-level findings curated for this source.
PMID:40352450
Siblings with a Homozygous Variant in the NHP2 Gene: A Case Report and Review of Literature.
No top-level findings curated for this source.
CGGV:assertion_a8fa9dcb-1cc6-43a2-8f86-e6cea0e6fce2-2025-08-01T160000.000Z
NHP2 / dyskeratosis congenita, autosomal recessive 2 (Limited)
No top-level findings curated for this source.

Deep Research

1

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Evaluations and curation notes (1)

Create: Dyskeratosis_Congenita_Autosomal_Recessive_2 · 2026-09-24T17:12:32Z · View source

De novo curation of DKCB2 (biallelic NHP2) as a standalone Disease entry, following the precedent of Dyskeratosis_Congenita_Autosomal_Recessive_6 (PARN) and _8: the parent Dyskeratosis_Congenita keeps its gene-keyed has_subtypes row for NHP2 and the disorder-family pathograph, while this entry carries the gene-specific upstream mechanism (H/ACA ribonucleoprotein assembly failure) that the family-level chain cannot express. Nine pathophysiology nodes run from failed NHP2 incorporation into the H/ACA complex through TERC depletion and telomerase insufficiency to telomere attrition, replicative senescence, marrow and mucocutaneous failure, clonal evolution, and a parallel ribosomal RNA biogenesis arm; two nodes declare conforms_to against telomere_attrition. Fifteen phenotypes, all quoted from cached sources. Cancer predisposition is carried on this entry rather than deferred to the parent, on the strength of one genetically confirmed NHP2 patient with myelodysplastic syndrome and gastric carcinoma plus genotype-based GeneReviews surveillance; no NHP2-specific quantitative risk figure exists and that gap is recorded as a discussion rather than filled. Sources: GeneReviews PMID:20301779 (baseline chapter, tagged), the ClinGen gene-disease validity assertion for NHP2/MONDO:0013519 (classification Limited, Interstitial Lung Disease GCEP, 2025-08-01), and six primary papers. PMID:36943377 and PMID:40073202 are on topic but have no retrievable text beyond their titles and were deliberately not cited. Deep research: falcon requested, returned HTTP 402 (out of credits), claude_code fallback produced the report; preflight-dr PASS, reference validation 8/8 verified with needs_review true on two unsupported quotes, term validation flagged five mislabelled identifiers in the report which were not adopted. Validated under linkml-reference-validator 0.3.0rc1: validate, count-verified-snippets 57/57, validate-terms, duplicate-keys, entity-refs, causal-targets, qualifier-terms, enum-values, coarse-phenotypes, snippet-length, title-snippets, snippet-grading, folded-hyphens, environmental-evidence, reference-titles, gene-term-mismatches, check-genereviews --online, pytest tests/test_data.py, and validate-disorders.

Claude Code ▸
Dyskeratosis Congenita, Autosomal Recessive 2 (DKCB2) — Research Report
claude-haiku-4-5-20251001, claude-sonnet-5 15 citations 2026-09-24T16:55:57.690787

Dyskeratosis Congenita, Autosomal Recessive 2 (DKCB2) — Research Report

MONDO:0013519 | OMIM #613987 | Gene: NHP2 (HGNC:14377, NCBI Gene 55651, chr5q35.3, NM_017838) | Also known as: NOLA2-related dyskeratosis congenita; DKCB2

Given your background, I'm skipping the general explanation of AR inheritance mechanics, penetrance/expressivity concepts, and mosaicism, and leading with the disease-specific claims and their sources. This is an ultra-rare entity — worldwide, published cases number in the single digits to low teens — so several template sections below have thin or no NHP2-specific literature; I've flagged those rather than padding with generic dyskeratosis congenita (DC) content that isn't gene-specific.

1. Disease Identity

DKCB2 is the biallelic-NHP2 subtype of dyskeratosis congenita / telomere biology disorder (DC/TBD). It was defined by Vulliamy et al. (PMID:18523010, PNAS 2008), who found compound-heterozygous or homozygous NHP2 variants in 2 of 117 DC patients screened, both Turkish [OMIM #613987]. It sits within the broader DC/TBD nosology alongside the AD forms (TERC, TERT, TINF2, RTEL1, PARN, ACD) and the other AR/XL forms (DKC1 X-linked; NOP10/DKCB1; WRAP53/TCAB1/DKCB3; biallelic RTEL1, PARN, ACD). GeneReviews treats DC and related TBDs as a single clinical spectrum ("Dyskeratosis Congenita and Related Telomere Biology Disorders," Savage & Niewisch, NBK22301) rather than splitting management guidance by causal gene — worth flagging for lump/split purposes: OMIM assigns NHP2 its own phenotypic MIM (613987/DKCB2), but clinical practice does not distinguish it from other AR-TBD forms except by molecular diagnosis.

  • ICD-10: Q82.8 (Other specified congenital malformations of skin) — not gene-specific; DC/TBD as a class has no dedicated ICD-10/11 code.
  • Orphanet: ORPHA:1775 covers dyskeratosis congenita generically; I did not find an NHP2-specific ORPHA subtype code in this pass — worth verifying directly against Orphadata XML before binding mappings.mondo_mappings/ORPHA in a KB entry.
  • ClinGen gene-disease validity: NHP2–dyskeratosis congenita is classified Limited by the ClinGen Syndromic Disorders GCEP, "at the higher end of the Limited classification point range, likely to change classification with one or two additional studies" (ClinGen Syndromic Disorders GCEP curation, cf. PMC11601709/PMC12151239, 2024). This is a materially weaker validity tier than DKC1, TERT, or TINF2, and reflects the very small published case count — worth surfacing explicitly if this goes into a KB entry rather than treating gene-disease validity as settled.

Source basis: the disease-level facts above come from a structured database (OMIM, ClinGen) plus the two primary case-series/functional papers below (PMID:18523010; the 2023 HMG functional paper) — I have not independently verified every detail against the primary PDFs (PNAS and PMC fetches were blocked by 403/CAPTCHA in this session; abstracts below are reconstructed from search-engine snippets, not read in full), so treat quoted fragments as leads to re-verify against the primary text before using them as curation snippets.

2. Etiology

Causal factor: Biallelic (homozygous or compound-heterozygous) loss-of-function or hypomorphic missense variants in NHP2 (NOLA2). No environmental, infectious, or multifactorial contribution is described for this subtype — DC/TBD as a class is a monogenic telomere-maintenance disorder.

Reported variants (all missense to date, consistent with an essential gene where complete loss is likely non-viable or embryonic-lethal, by analogy to the core-complex partner genes):

Variant Zygosity Source
p.Tyr139His (c.415T>C) Homozygous, 22-y-old Turkish man PMID:18523010; also OMIM #613987
p.Val126Met (c.376G>A) (second Turkish proband; ClinVar RCV000004502) PMID:18523010
p.Ala39Thr (c.115G>A) Compound heterozygous 2023 Hum Mol Genet functional paper (PMC10508036)
p.Thr44Met (c.131C>T) Compound heterozygous (with A39T, above) same

Functional mechanism of the variants: V126M and Y139H "impaired association with NOP10, leading to major pre-RNP assembly defects with all H/ACA RNAs tested, including the H/ACA domain of hTR [TERC]" (search-derived summary of PMID:20008900, Trahan & Dragon, Hum Mol Genet 2010 — re-verify wording against primary text). A39T and T44M destabilize the NHP2 N-terminal domain via molecular-dynamics-demonstrated distortion of residues 33–41 (A39T) and residues 1–24 (T44M), driving proteasomal degradation of the mutant protein when competing with wild-type NHP2 for RNP incorporation, with consequent reduction in hTR levels and telomerase activity (2023 HMG paper, PMC10508036).

Risk/protective/gene-environment factors: No NHP2-specific modifier genes, environmental risk factors, or protective variants have been reported in the literature I could locate — this is a gap, not a documented absence, given how few cases exist to study. General TBD literature (not NHP2-specific) notes that even within families carrying an identical variant, disease severity varies considerably (per GeneReviews) — consistent with genetic-anticipation-type telomere-length inheritance effects seen across DC/TBD broadly, but this has not been specifically demonstrated for NHP2 pedigrees in the sources I found.

3. Phenotypes

The classic DC mucocutaneous triad plus multisystem stem-cell-exhaustion features, as reported for the ~4 published NHP2 patients (2 Vulliamy 2008; 1 index case in the 2023 HMG functional paper; a sibling pair in a 2025 case report, PMID:40352450, PMC12065628 — full text not retrievable in this session, only stub metadata confirmed).

Phenotype Suggested HP term Notes
Nail dystrophy HP:0008404 Classic triad component
Reticulated/lacy skin hyperpigmentation HP:0007441 Classic triad component
Oral leukoplakia HP:0002745 Classic triad component
Progressive bone marrow failure / aplastic anemia HP:0005528 "Principal cause of mortality in DC patients" per GeneReviews (general DC/TBD claim)
Thrombocytopenia HP:0001873 Index Y139H patient
Myelodysplastic syndrome HP:0002863 2023 HMG index case, age 38
Premature graying of hair HP:0002216 GeneReviews general feature list
Testicular atrophy HP:0000029 Y139H patient (OMIM)
Growth delay HP:0001510 Y139H patient (OMIM: "growth ... retardation")
Intellectual disability HP:0001249 Y139H patient (OMIM: "mental retardation")
Hepatic fibrosis / cirrhosis HP:0001394 Y139H patient ("liver cirrhosis")
Intracranial calcification HP:0002514 Y139H patient
Recurrent/opportunistic infection HP:0002719 Y139H patient
Pulmonary fibrosis HP:0002206 General DC/TBD feature; not confirmed NHP2-specific in sources found
Gastric cancer HP:0012126 (neoplasm of stomach, approximate) 2023 HMG index case, age 38

Frequencies: with only ~4 published patients, no meaningful phenotype-frequency percentages can be derived for the NHP2 subtype specifically. The Y139H patient's phenotype (testicular atrophy, growth/intellectual impairment, intracranial calcification, opportunistic infection) is notably severe for an adult-diagnosed case (age 22) and approaches the Hoyeraal-Hreidarsson-syndrome end of the DC severity spectrum, though I did not find an explicit HH designation applied to this patient in the sources retrieved — flag rather than assert if curating.

QoL data: none specific to NHP2 located; general DC/TBD QoL literature was not pursued given the gene-level focus requested.

4. Genetic/Molecular Information

  • Gene: NHP2 ribonucleoprotein (HGNC:14377; NCBI Gene 55651; chr5q35.3; aliases NOLA2, NHP2P, SPAG12, DKCB2).
  • Variant classification: All reported variants are missense; ClinVar lists p.Val126Met (NM_017838.4:c.376G>A) as pathogenic for "Dyskeratosis congenita, autosomal recessive 2" (RCV000004502).
  • Functional impact category: loss-of-function via protein destabilization/misfolding and impaired complex incorporation (not classic catalytic-site LOF) — PARTIAL_LOSS_OF_FUNCTION is likely the most accurate FunctionalImpactEnum value pending confirmation against the primary functional papers, since residual telomerase activity is reduced but not abolished in the biochemical assays described.
  • Population frequency: no NHP2 pathogenic-variant carrier frequency or gnomAD allele-frequency data specific to these variants was retrieved in this pass — check gnomAD directly for p.Tyr139His/p.Val126Met/p.Ala39Thr/p.Thr44Met before citing a number.
  • Somatic vs. germline: exclusively germline; DC/TBD is a constitutional disorder. (The secondary MDS/AML and squamous carcinomas that DC patients are predisposed to are separate somatic events arising in the germline-predisposed marrow/epithelium — keep these as distinct pathophysiology nodes/entries rather than folding them into the germline syndrome, consistent with design-decisions §3a.)
  • Epigenetics/structural variation: none reported for this gene/subtype in the sources retrieved.

5. Environmental Information

No NHP2-specific environmental, lifestyle, or infectious contributory factors are reported. General DC/TBD clinical guidance (not NHP2-specific) advises avoiding additional telomere/marrow stressors (e.g., excess sun exposure given SCC risk, hepatotoxic exposures given fibrosis risk) but I did not find this stated as NHP2-specific literature — would need to be sourced from GeneReviews management sections rather than asserted as disease-specific etiology.

6. Mechanism / Pathophysiology

Causal chain (numbered), noting where each step is directly demonstrated vs. inferred:

  1. Biallelic NHP2 missense variants (p.Tyr139His, p.Val126Met — PMID:18523010; p.Ala39Thr, p.Thr44Met — PMC10508036) destabilize the NHP2 protein or impair its N-terminal domain conformation. Demonstrated by molecular-dynamics simulation and cell-based degradation assays for A39T/T44M.
  2. This leads to impaired NHP2–NOP10 association and reduced/defective incorporation of NHP2 into the core H/ACA ribonucleoprotein complex (dyskerin–NOP10–NHP2–GAR1), with mutant protein undergoing proteasome-dependent degradation when competing against wild-type. Demonstrated (PMID:20008900; PMC10508036).
  3. This results in defective assembly of H/ACA snoRNPs generally and, specifically, of the H/ACA domain of TERC (the telomerase RNA component), which depends on this same core complex for stability. Demonstrated for V126M/Y139H (PMID:20008900).
  4. This leads to reduced steady-state TERC (hTR) levels — "patients with NHP2 mutations, in common with patients bearing dyskerin and NOP10 mutations, had short telomeres and low TERC levels" (PMID:18523010, paraphrased from search snippet — re-verify exact wording against primary text before quoting as a KB snippet).
  5. Reduced TERC availability results in diminished assembly and activity of the telomerase holoenzyme (telomerase reverse transcriptase + TERC + accessory H/ACA proteins). Demonstrated directly for A39T/T44M via reduced telomerase activity assays (PMC10508036).
  6. Insufficient telomerase activity leads to progressive, division-coupled telomere shortening, most consequential in high-turnover stem/progenitor compartments (hematopoietic stem cells, epidermal/mucosal basal keratinocytes, germ cells, alveolar and hepatic progenitor populations). Inferred by extension from the general DC/TBD mechanism — telomere length was not independently measured in the NHP2 cohort beyond "short" per the cited source.
  7. Critically short telomeres trigger a persistent DNA-damage response, replicative senescence, and apoptosis in affected stem/progenitor pools, causing tissue-specific stem-cell exhaustion. Inferred, extrapolated from the general DC/TBD literature rather than NHP2-specific data.
  8. Stem-cell exhaustion manifests as: (a) hematopoietic stem cell attrition → progressive trilineage bone marrow failure (thrombocytopenia documented in the index case); (b) epithelial stem-cell attrition → nail dystrophy, mucosal leukoplakia, skin pigmentation changes; (c) hepatic/pulmonary progenitor attrition → organ fibrosis (liver cirrhosis documented in the Y139H patient); (d) germline stem-cell attrition → testicular atrophy (documented).
  9. Branch — malignant transformation (distinct somatic process, not part of the germline mechanism above): chronic replicative stress and genomic instability in the exhausted, telomere-crisis-prone marrow and epithelium predisposes to acquisition of somatic driver mutations, manifesting as myelodysplastic syndrome (documented in the 2023 index case) and, by extension from general DC biology, squamous cell carcinoma and AML. This should be modeled as a separate somatic pathophysiology branch downstream of the germline telomere-maintenance defect, per the germline/somatic separation convention.

Second, less-established mechanistic thread — ribosome biogenesis: because NHP2/dyskerin/NOP10/GAR1 form the core machinery for essentially all box H/ACA snoRNPs (not only the telomerase-associated one), and box H/ACA snoRNPs guide pseudouridylation of ribosomal RNA, some literature frames DC as having a partial ribosomopathy component alongside the telomere defect. I did not find this explicitly demonstrated for the NHP2 subtype specifically in this pass (it is more thoroughly documented for DKC1-associated X-linked DC); flag as a plausible but unconfirmed-for-NHP2 mechanistic branch rather than asserting it.

Suggested GO terms: telomerase activity (GO:0003720), telomere maintenance via telomerase (GO:0007004), box H/ACA snoRNP assembly (GO:0031120), pseudouridine synthesis (GO:0001522), telomerase RNA stabilization (no precise GO term confirmed — verify via OAK before binding).

Suggested cell types (CL): hematopoietic stem cell (CL:0000037), epidermal keratinocyte (CL:0000312), basal cell of epidermis, hepatocyte/hepatic stellate cell (fibrosis), spermatogonial stem cell.

7. Anatomical Structures Affected

  • Primary organs: bone marrow (UBERON:0002371), skin/nail unit (UBERON:0001003 epidermis; nail plate), oral mucosa (UBERON:0003729).
  • Secondary/complication organs: liver (UBERON:0002107 — fibrosis/cirrhosis documented), lung (UBERON:0002048 — fibrosis reported generally for DC/TBD, not confirmed NHP2-specific here), testis (UBERON:0000473 — atrophy documented), CNS (intracranial calcification documented in one patient).
  • Body systems: hematologic, integumentary, hepatic, reproductive (male), and — per general DC/TBD biology rather than NHP2-specific confirmation — respiratory and skeletal (osteoporosis).
  • Subcellular: nucleolus (site of H/ACA snoRNP assembly), Cajal bodies (TCAB1/WRAP53-mediated telomerase trafficking — relevant to the pathway family though not NHP2 itself specifically), telomeres (chromosome ends).

8. Temporal Development

The Y139H patient presented at age 22 (Vulliamy 2008); the 2023 HMG index case presented in adulthood (age 38) with MDS and gastric cancer as the presenting/index features rather than classic pediatric mucocutaneous triad. This is notable: unlike the more common AD (TERT, TINF2) and X-linked (DKC1) forms, which often present in childhood, the published NHP2 cases skew toward later-childhood/adult presentation, though the n is far too small (~4 patients) to generalize a typical age-of-onset or progression pattern. No formal staging system exists for DC/TBD; general GeneReviews guidance frames it as a progressive, generally non-remitting stem-cell-exhaustion disorder with bone marrow failure as the dominant driver of mortality across the DC/TBD class as a whole.

9. Inheritance and Population

  • Inheritance: autosomal recessive (biallelic NHP2 variants required); HP:0000007.
  • Prevalence: DC/TBD overall is estimated at roughly 1:1,000,000; NHP2 pathogenic variants account for less than 1% of all dyskeratosis congenita cases (GeneReviews, NBK22301) — making DKCB2 one of the rarest molecularly defined DC subtypes. No NHP2-specific incidence/prevalence figure exists; prevalence_class: ULTRA_RARE / NOT_YET_DOCUMENTED with measure_type: CASES_IN_LITERATURE would be the honest framing for a KB entry given only ~4 published cases.
  • Population/ancestry: the two founding cases were Turkish (Vulliamy 2008); no founder-effect or specific-population enrichment has been established from this small case count — a shared ancestry between the two original probands raises consanguinity as a plausible but unconfirmed factor (not stated explicitly as consanguineous in the retrieved abstract fragments — verify against full text).
  • Sex ratio, geographic distribution: insufficient case count to characterize.
  • Penetrance/expressivity: general DC/TBD literature (GeneReviews) states penetrance "varies considerably, even within families with identical variants" — this is a class-level statement, not one independently demonstrated for NHP2 pedigrees specifically in the sources found.

10. Diagnostics

  • Primary diagnostic test (class-level, per GeneReviews, applies to NHP2 as to other DC/TBD genes): lymphocyte telomere length by flow-FISH, showing values below the 1st percentile for age, combined with either clinical diagnostic criteria or biallelic pathogenic NHP2 variants on molecular testing.
  • Molecular testing: multigene DC/TBD panel or exome sequencing; "sequence analysis has detected pathogenic variants in all studied NHP2 families" (GeneReviews) — i.e., no large structural variants have been reported for this gene in the DC context.
  • Laboratory: low TERC levels have been demonstrated biochemically in NHP2 patients specifically (PMID:18523010), which is a distinguishing molecular signature shared with DKC1- and NOP10-associated disease (all three encode core H/ACA RNP components) but not with TERT/TINF2/RTEL1-associated disease (where TERC itself is not depleted).
  • Differential diagnosis: the other 8+ molecularly defined DC/TBD genes; Fanconi anemia (bone marrow failure + some overlapping congenital features — distinguish via chromosome breakage/DEB testing and telomere length, which is normal in FA); Hoyeraal-Hreidarsson syndrome (severe end of the DC/TBD spectrum — the Y139H patient's phenotype approaches this).
  • Screening: no population or newborn screening program exists for DC/TBD; family cascade testing is appropriate once a proband's biallelic NHP2 variants are identified, given AR inheritance and the implied ~25% recurrence risk in future sibs of carrier parents.

11. Outcome/Prognosis

Insufficient NHP2-specific cohort data exists for survival statistics. Class-level DC/TBD data (GeneReviews) states bone marrow failure is the principal cause of mortality; solid-organ (pulmonary fibrosis, hepatic disease) and secondary-malignancy (MDS/AML, SCC) complications are the other major drivers of morbidity/mortality across DC/TBD broadly. Within the NHP2 case reports specifically: the 2023 index patient developed both MDS and gastric adenocarcinoma by age 38 — a data point consistent with, but not proof of, the general DC malignancy-predisposition pattern extending to this subtype.

12. Treatment

No NHP2-specific treatment trial or outcome data exists; management follows general DC/TBD guidance (GeneReviews):

  • Hematopoietic cell transplantation (NCIT:C15431) — the only curative approach for bone marrow failure; DC/TBD patients require reduced-intensity/fludarabine-based conditioning given radiosensitivity and organ fragility (class-level guidance, not NHP2-specific confirmation found).
  • Androgens (e.g., danazol, oxymetholone; NCIT:C15986 Pharmacotherapy + CHEBI therapeutic_agent) — used off-label to stimulate hematopoiesis when transplant is not immediately available/suitable, per class-level DC/TBD guidance.
  • Supportive/surveillance care: per GeneReviews — annual CBC and marrow evaluation, monthly self skin/mucosal exams plus annual dermatology and otolaryngology exams (SCC surveillance), pulmonary function testing from ~age 8, semi-annual dental evaluation.
  • Genetic counseling (NCIT:C15240) — appropriate given AR inheritance and availability of molecular carrier/prenatal testing once the familial variants are known.
  • No gene therapy, RNA-based therapy, or targeted molecular therapy specific to NHP2/telomerase restoration has reached clinical trials for this subtype; I found no registered NCT trial specific to NHP2-DC in this pass (would need a direct ClinicalTrials.gov search restricted to "NHP2" or "dyskeratosis congenita" to confirm absence rather than asserting it from a general search).

13. Prevention

No primary prevention exists (germline monogenic disorder). Secondary prevention is carrier/prenatal testing and preimplantation genetic diagnosis once familial variants are identified, per standard AR-disorder genetic counseling practice — not NHP2-specific literature. Tertiary prevention is the surveillance program under Diagnostics/Treatment above (cancer screening, pulmonary monitoring) aimed at early detection of DC/TBD complications.

14. Other Species / Natural Disease

No naturally occurring NHP2-associated disease in non-human species was located in this search pass (no OMIA entry found for NHP2/DKCB2-equivalent veterinary disease). NHP2 is broadly conserved (ortholog present across vertebrates given its essential role in H/ACA snoRNP biology and ribosome synthesis), but disease-causing biallelic variants have only been reported in humans.

15. Model Organisms

  • Mouse: Nhp2 (MGI:1098547), chromosome 11 (syntenic band 11B1.3), human ortholog confirmed. I did not find a published disease-modeling Nhp2 knockout/knock-in mouse paper specific to DC phenotype recapitulation in this search pass — this is a notable gap relative to the Terc−/−, Dkc1 hypomorphic, and Tinf2 mouse models that are well-characterized in the DC/TBD literature. Given Nhp2's essential role in ribosome biogenesis generally (not just telomerase), a complete knockout is plausibly embryonic lethal, which may explain why disease-modeling has favored patient-variant knock-in approaches or has simply not yet been published for this gene — this is my inference, not a sourced claim, and should be verified directly (e.g., via MGI phenotype records or IMPC) before use.
  • Cellular models: patient-derived and engineered cell lines expressing mutant NHP2 (A39T, T44M) were used directly in the 2023 functional study (PMC10508036) to demonstrate reduced telomerase activity and hTR levels — this is the strongest "model system" evidence available for this subtype, though it is a cellular/in-vitro model rather than an organismal one, and fidelity to the whole-organism human phenotype (marrow failure, organ fibrosis) is not established by this data alone.

Summary of Confidence and Gaps

This is a genuinely thin literature — roughly 4 published patients across 3 papers spanning 2008–2025, and a ClinGen validity classification of only Limited. The strongest, most directly sourced claims are the gene identity, the specific variants, and the H/ACA RNP-assembly/TERC-depletion mechanism (PMID:18523010; PMID:20008900; PMC10508036). The weakest are anything requiring cohort-level statistics (prevalence, penetrance, age-of-onset distribution, treatment response rates) and the model-organism section, where I found no NHP2-specific animal model. Several PubMed/PMC/PNAS full-text fetches were blocked (403/CAPTCHA) in this session, so quoted fragments above are reconstructed from search-engine result snippets rather than read directly from primary text — before using any of these as a KB snippet:, re-fetch the primary source (just fetch-reference PMID:18523010 etc.) and re-verify the exact quoted substring.

Sources consulted: - OMIM #613987 — Dyskeratosis Congenita, Autosomal Recessive 2 - OMIM *606470 — NHP2 Ribonucleoprotein - PubMed 18523010 — Vulliamy et al., "Mutations in the telomerase component NHP2 cause the premature ageing syndrome dyskeratosis congenita," PNAS 2008 - PNAS full text (fetch blocked, HTTP 403) - PubMed 20008900 — Trahan & Dragon, "Effects of dyskeratosis congenita mutations in dyskerin, NHP2 and NOP10 on assembly of H/ACA pre-RNPs," Hum Mol Genet 2010 - PMC10508036 — "Novel pathological variants of NHP2 affect N-terminal domain flexibility, protein stability, H/ACA RNP complex formation and telomerase activity," Hum Mol Genet 2023 - PubMed 40352450 / PMC12065628 — "Siblings with a Homozygous Variant in the NHP2 Gene: A Case Report and Review of Literature," 2025 - GeneReviews NBK22301 — Savage & Niewisch, "Dyskeratosis Congenita and Related Telomere Biology Disorders" - ClinGen — NHP2 curation results (MONDO:0013519) - ClinGen Syndromic Disorders GCEP — 111 gene-disease relationships (PMC11601709/PMC12151239, 2024) - ClinVar RCV000004502 — NHP2 c.376G>A (p.Val126Met) - NIH GTR — Dyskeratosis congenita, autosomal recessive 2 - MGI — Nhp2 mouse gene detail (MGI:1098547) - GeneCards — NHP2 - Orphanet — Dyskeratosis congenita (ORPHA:1775)

Reference Validation

Checked with linkml-reference-validator 0.3.0rc1.

Outcome Count
References checked 8
Resolved 8
Unresolved (possible confabulation) 0
Unverifiable 0
Quoted claims checked 4
Quoted claims found in source 2
Quoted claims not found in source 2
References weighed for topical relevance 8
On topic 6
Off topic 0

Quotes not found in the cited source

Searched the abstract, any retrieved full text, and the title. A quote drawn from a part of the paper that was not retrieved will appear here too, so check before treating one as invented:

Every one of these was searched against an abstract alone, with no full text retrieved - marked abstract only below. Where full text can be fetched, re-running with it will settle them; where the source publishes only a summary to PubMed, as GeneReviews chapters do, it will not, and the quote has to be checked by hand against the chapter itself.

  • PMC:PMC11601709 (abstract only): "at the higher end of the Limited classification point range, likely to change classification with one or two additional studies"
  • closest text in source: "A full review of 111 GDRs for 100 genes followed, with 78 classified as Definitive, 9 as Strong, 15 as Moderate, and 9 as Limited highlighting where further data are needed"
  • PMC:PMC12151239 (abstract only): "at the higher end of the Limited classification point range, likely to change classification with one or two additional studies"
  • closest text in source: "A full review of 111 GDRs for 100 genes followed, with 78 classified as Definitive, 9 as Strong, 15 as Moderate, and 9 as Limited, highlighting cases in which further data are needed"

Term Validation

Checked with linkml-term-validator 0.4.5, through the ols: adapter.

Outcome Count
Terms checked 35
Resolved 32
Unresolved (possible confabulation) 0
Obsolete 0
Unverifiable 3
Terms whose name was checked 21
Terms named correctly 10
Terms named as a different term 5
Terms whose name is worth a second look 6

Terms the report names something else

These identifiers resolve, so nothing about them looks wrong, and the ontology calls them something unrelated to what the report calls them. That usually means the identifier is not the one the sentence needs:

  • HP:0007441 (1 mention) - the report calls it "Reticulated/lacy skin hyperpigmentation"; HP calls it Hyperpigmented/hypopigmented macules
  • HP:0012126 (1 mention) - the report calls it "neoplasm of stomach, approximate"; HP calls it Stomach cancer
  • UBERON:0002107 (1 mention) - the report calls it "fibrosis/cirrhosis documented"; UBERON calls it liver
  • UBERON:0002048 (1 mention) - the report calls it "fibrosis reported generally for DC/TBD, not confirmed NHP2-specific here"; UBERON calls it lung
  • UBERON:0000473 (1 mention) - the report calls it "atrophy documented"; UBERON calls it testis

Terms whose name is worth a second look

The report's name for these is recognisably related to the term's own name without being one of them. A loose paraphrase reads the same way as a citation of the wrong sibling term - and so does a related synonym, which the ontology records precisely because it names something adjacent rather than the same thing - so these are listed rather than judged:

  • HP:0005528 (1 mention) - the report calls it "Progressive bone marrow failure / aplastic anemia"; HP calls it Bone marrow hypocellularity, and lists "Bone marrow failure" among its other names
  • HP:0002863 (1 mention) - the report calls it "Myelodysplastic syndrome"; HP calls it Myelodysplasia, and lists "Myelodysplastic syndrome" among its other names
  • HP:0001394 (1 mention) - the report calls it "Hepatic fibrosis / cirrhosis"; HP calls it Cirrhosis, and lists "Hepatic cirrhosis" among its other names
  • HP:0002514 (1 mention) - the report calls it "Intracranial calcification"; HP calls it Cerebral calcification
  • HP:0002719 (1 mention) - the report calls it "Recurrent/opportunistic infection"; HP calls it Recurrent infections
  • UBERON:0002371 (1 mention) - the report calls it "Primary organs: bone marrow"; UBERON calls it bone marrow**

Terms named inconsistently

The report gives these identifiers more than one name of its own:

  • MGI:1098547 - called "Nhp2", "Mouse:* Nhp2"

Prefixes with no resolver

Terms carrying these prefixes were not checked either way, because no configured ontology covers them. An unrecognised prefix may name an ontology this run could not reach as easily as one that does not exist, so nothing here is evidence of fabrication: ORPHA, MGI.