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Mappings

MONDO

MONDO:0016410 central congenital hypothyroidism DisMech

MONDO:0010139 is a child of MONDO:0016410, which is curated separately as kb/disorders/Central_Congenital_Hypothyroidism.yaml. Recorded as broadMatch so the relationship between the two entries is queryable from this side rather than implicit. Note that broadMatch deliberately does not retire the parent concept from the curation queue, which is correct here: this entry curates the TSHB entity, not the category.

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Inheritance

1

Autosomal recessive HP:0000007

Biallelic TSHB variants, homozygous or compound heterozygous. Consanguinity is the usual setting for the homozygous cases and was how the disorder was first delineated; the recurrent c.373delT allele also appears in compound heterozygotes with a second TSHB lesion.

Autosomal recessive inheritance

Show evidence (2 references)

PMID:34981755 SUPPORT BACKGROUND Human Clinical

"Bi-allelic loss-of-function mutations in TSHB, encoding the beta subunit of thyroid-stimulating hormone (TSH), cause congenital hypothyroidism."

States the biallelic requirement. Marked BACKGROUND because this paper's own subject is the non-pathogenic R75G variant; the sentence is its framing of the established disease.

PMID:27362444 SUPPORT Human Clinical

"the affected individuals were compound heterozygous for TSHB c.373delT and either a 5·4-kB TSHB deletion"

Compound heterozygosity, confirming that two damaged alleles rather than one are needed.

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Discussions and Knowledge Gaps

3

A TSHB variant in a person with a low or undetectable TSH is not necessarily a cause of this disease. How should p.R75G be distinguished from a pathogenic TSHB allele?

INTERPRETATION OPEN tshb_r75g_assay_interference_not_disease

Attached to

genetic#TSHB biochemical#Serum Thyrotropin (TSH)

The p.R75G variant is common - about 4% carrier frequency in Bene Israel Indian Jews, on a haplotype shared with South Asian populations - and does not impair TSH function. What it does is defeat detection of TSH on some immunoassay platforms, so carriers who are clinically euthyroid appear to have a low or undetectable TSH and have been diagnosed with hyperthyroidism in error. It is the mirror image of this disease: the same gene, a low measured TSH, and the opposite clinical meaning. The discriminator is the free T4. In this disease free T4 is low; in R75G carriers it is normal and the patient is euthyroid. The platform matters too - the discrepancy is assay-dependent, so re-measuring on a different platform is informative. Recorded as an interpretation question rather than a knowledge gap because the biology is settled; what is unsettled is how reliably it is applied at the bench. This entry's own curation nearly got it wrong: the variant reads in a title search as a founder pathogenic allele, and it took reading the abstract to see that the paper is about euthyroid people.

Show evidence (2 references)

PMID:34981755 REFUTE DIRECT Human Clinical

"Homozygosity for the TSHB p.R75G variant, previously described in South Asian individuals, does not alter TSH function but abrogates its detection by some immune detection-based platforms, leading to erroneous diagnosis of hyperthyroidism."

A REFUTE item against treating p.R75G as a cause of this disease. The variant is explicitly stated not to alter TSH function.

PMID:34981755 SUPPORT DIRECT Human Clinical

"Extremely high carrier rate of p.R75G TSHB in Bene Israel Indian Jews (~4%) was observed."

The carrier frequency, which is what makes this a practical differential rather than a curiosity.

How many cases of TSHB-related congenital central hypothyroidism are missed by TSH-only newborn screening, and what is the neurodevelopmental cost?

KNOWLEDGE GAP OPEN tshb_screening_analyte_determines_outcome

Attached to

pathophysiology#Invisibility to TSH-Based Newborn Screening

The disorder is preventable and the intervention is cheap, so the number that matters is how many children are not found. It cannot be read off the literature: the Dutch T4-based figure of up to 1:16 000 is for central congenital hypothyroidism as a whole, the TSHB share of that is unquantified, and the countries where the miss occurs are by construction the ones with no denominator. The case series report late diagnoses at five months, at twelve years and after neurodevelopmental damage had occurred, but a case series cannot give a rate. This is a knowledge gap with an unusual property: closing it would not change what we know about the biology at all, and would change practice immediately.

Should IGSF1, TBL1X, TRHR and IRS4 central hypothyroidism be curated as separate dismech entries, and should a grouping hold them together with this one?

CURATION TODO OPEN tshb_entity_boundary_versus_other_cch_genes

Attached to

disease#Isolated Thyroid-stimulating Hormone Deficiency

Clinically these five are one differential - a child with a low free T4 and a non-elevated TSH - and the published reviews treat them as one entity. Mechanistically they are not one thing: TSHB removes the hormone, while IGSF1, TBL1X, TRHR and IRS4 act on the regulatory machinery upstream of it, and each carries extrathyroidal features the others do not. This entry therefore curates only the TSHB entity. Two concrete follow-ups, neither actioned here because both change a file this curation PR has no business touching: 1. `kb/disorders/Central_Congenital_Hypothyroidism.yaml` (MONDO:0016410) carries no `mappings.mondo_mappings` block at all and does not cite MONDO:0010139. This entry now records the relationship from its own side as a `skos:broadMatch`, but the parent does not record it reciprocally, so a reader arriving at the parent has no signal that the TSHB entity is curated separately. Its "TSHB pathogenic variants" genetic row is the obvious place for a cross-reference. 2. IGSF1, TBL1X, TRHR and IRS4 each have their own MONDO term and none is curated as a dismech entry. Once two or more exist, a `kb/groupings/` record over the clinical differential would capture it without collapsing the mechanisms, which is what a grouping is for. A grouping built now would have one disease member and would encode this entry rather than the category. Raised by the automated second-opinion comment on dismech#12392, which found the parent entry and argued the subtype case. The scope note above is the answer; these are the parts of its argument that stand.

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Pathophysiology

5

Biallelic TSHB Loss of Function

Two damaged TSHB alleles. The reported lesion classes are a recurrent frameshift (p.Cys105Valfs*114), missense alleles including the exon-2 change that defined the disorder in three consanguineous Japanese families, a start-loss allele p.Met1?, and a 5.4-kb whole-gene deletion. Note that the recurrent frameshift is cited in the literature under two cDNA numberings, c.373delT and c.313delT, depending on whether the signal peptide is counted; they are the same allele, and this entry names it at protein level to avoid implying they are two.

TSHB hgnc:12372

Genetic context TSHB hgnc:12372 variant_origin: GERMLINE zygosity: HOMOZYGOUS functional_impact_category: LOSS_OF_FUNCTION

Homozygous in the consanguineous and founder pedigrees; compound heterozygous in the UK and Ireland kindreds, where the recurrent frameshift was paired with a large deletion or a start-loss allele.

Downstream

Failure to Assemble Bioactive TSH Heterodimer Without an intact beta subunit the alpha subunit has no thyrotropin-specific partner to pair with.

Show evidence (2 references)

PMID:27362444 SUPPORT DIRECT Human Clinical

"Homozygous mutations in the TSH beta subunit gene (TSHB) result in severe, isolated, central congenital hypothyroidism (CCH)."

States the gene-disease relationship and the zygosity requirement.

PMID:1762181 SUPPORT DIRECT Human Clinical

"They had a same missense mutation in the 2nd exon of the TSH beta-subunit gene"

The founding molecular observation, in three consanguineous Japanese families.

Failure to Assemble Bioactive TSH Heterodimer

TSH is a heterodimer of a shared alpha subunit and the TSHB-encoded beta subunit; the beta subunit is what confers thyrotropin specificity. The frameshift allele has been characterised at the receptor rather than merely inferred: the mutant hormone diminishes cAMP signalling at TSHR, and does not induce phospholipase C activation at all, while - unexpectedly - leaving MAPK signalling comparable to wild type. So the lesion is a selective loss across TSHR's signalling arms rather than a uniform silencing of the receptor.

pituitary thyrotroph CL:0000476

thyroid-stimulating hormone signaling at TSHR GO:0038194 ↓ DECREASED

adenohypophysis UBERON:0002196

Downstream

Invisibility to TSH-Based Newborn Screening The same absent bioactive heterodimer that fails to stimulate the thyroid is also the analyte a TSH-based screening programme measures. A screen looking for raised TSH therefore reads normal in exactly the patients who have none, which is why the detection failure is a consequence of the molecular lesion rather than a separate root.

Understimulation of the Normal Thyroid Gland The thyroid is structurally intact but receives no adequate trophic signal.

Show evidence (4 references)

PMID:31703413 SUPPORT DIRECT In Vitro

"The patient mutation C105Vfs114X and further designed TSH mutants diminished cyclic adenosine monophosphate (cAMP) signaling activity."

Direct receptor-level measurement of what the mutant hormone fails to do.

PMID:31703413 SUPPORT DIRECT In Vitro

"Surprisingly, MAPK signaling for all mutants was comparable to WT, while none of the mutants induced PLC activation."

Establishes that the loss is arm-selective, not a global failure of the receptor - which is why the node describes a modified rather than an abolished signal.

PMID:2792087 SUPPORT DIRECT In Vitro

"Microinjection of the mutated beta mRNAs into Xenopus laevis oocytes led to the formation of conformationally altered beta polypeptides that could not associate with alpha subunits."

The direct demonstration that this node asserts: the mutant beta subunit is misfolded and cannot pair with the alpha subunit, so no heterodimer forms. This is a failure of assembly rather than of production, and it is why the disorder is not a failure of pituitary drive.

+ 1 more reference

Understimulation of the Normal Thyroid Gland

Thyroid follicular cells do not receive the cAMP-mediated trophic and secretory signal they depend on, so thyroid hormone synthesis and release fall. The gland is not goitrous and is not intrinsically abnormal, which is what distinguishes this from primary congenital hypothyroidism and gives the disorder its OMIM name, congenital non-goitrous hypothyroidism.

thyroid follicular cell CL:0002258

thyroid hormone generation GO:0006590 ↓ DECREASED

thyroid gland UBERON:0002046

Downstream

Systemic Thyroid Hormone Deficiency Reduced synthesis and secretion lower circulating free T4 and free T3.

Show evidence (1 reference)

PMID:26416826 SUPPORT DIRECT REVIEW SYNTHESIS Other

"Central congenital hypothyroidism (CCH) is a rare disorder in which inadequate thyroid hormone biosynthesis occurs due to defective stimulation of a normal thyroid gland by thyroid stimulating hormone (TSH)."

Names both halves of this node: reduced hormone biosynthesis, in a structurally normal gland.

Systemic Thyroid Hormone Deficiency

Low circulating free T4 and free T3 from birth, with a TSH that is low, normal or undetectable and does not rise. Thyroid hormone is required for central nervous system myelination and maturation, for linear growth and for basal metabolic rate, so the deficiency is expressed across all three. The severity is comparable to athyreosis rather than to a partial biosynthetic defect, which was not what the field expected of a TSHB lesion.

thyroid hormone receptor signaling in peripheral tissues GO:0002154 ↓ DECREASED

Downstream

Central hypothyroidism The defining biochemical phenotype.

Global developmental delay Untreated neonatal thyroid hormone deficiency during the period of CNS maturation. Preventable, not inevitable.

Hypothermia A systemic consequence of the thyroid hormone deficit, presenting in the same first weeks of life as the other untreated features.

Lethargy A systemic consequence of the thyroid hormone deficit, presenting in the same first weeks of life as the other untreated features.

Constipation A systemic consequence of the thyroid hormone deficit, presenting in the same first weeks of life as the other untreated features.

Umbilical hernia A systemic consequence of the thyroid hormone deficit, presenting in the same first weeks of life as the other untreated features.

Hypotonia Thyroid hormone is required for normal neuromuscular tone; its systemic deficiency presents in the first weeks of life with muscle hypotonia among the other signs of congenital hypothyroidism.

Failure to thrive Growth failure follows the systemic hormone deficiency, and is one of the features that brings an unscreened infant to attention.

Short stature The same growth failure carried forward: untreated thyroid hormone deficiency impairs skeletal growth and final height.

Intellectual disability The irreversible consequence, and the reason detection timing matters: thyroid hormone is required for central nervous system development in the first months of life.

Prolonged neonatal jaundice A common presenting sign, and often the reason the infant is investigated at all.

Show evidence (2 references)

PMID:31703413 SUPPORT DIRECT BACKGROUND Human Clinical

"Therefore, patients with a TSHB-gene mutation show a severe phenotype comparable to patients with athyreosis"

Calibrates the severity of the systemic deficiency against a reference condition. BACKGROUND because this in-vitro paper is restating the clinical literature here, not reporting its own patients.

PMID:31703413 SUPPORT DIRECT BACKGROUND Human Clinical

"Within the first weeks to months of life, affected patients present with severe signs of congenital hypothyroidism, including hypothermia, lethargy, prolonged jaundice, muscle hypotonia, constipation and umbilical hernias."

Enumerates the neonatal systemic manifestations. BACKGROUND for the same reason.

Invisibility to TSH-Based Newborn Screening

Curated as a node because in this disease the detection pathway determines the outcome as directly as the biology does. A TSH-based screening programme looks for a raised TSH; here TSH is low or undetectable, so an affected infant screens normal. Whether a child is found in the first week of life or months later therefore depends on which analyte their country's programme measures - T4-based programmes such as the Dutch heel-prick screen detect the condition, TSH-only programmes cannot. Everything downstream of this node is preventable.

Downstream

Global developmental delay The screening failure is upstream of the neurodevelopmental outcome, because the outcome is a function of how long the deficiency goes untreated.

Show evidence (2 references)

PMID:31166470 SUPPORT DIRECT Human Clinical

"Isolated TSH deficiency is not detected by routine TSH-based neonatal screening, representing a clinical challenge."

The direct statement of the screening failure.

PMID:26416826 SUPPORT DIRECT REVIEW SYNTHESIS Other

"Since TSH is not elevated, CCH will evade diagnosis in primary, TSH-based, CH screening programs and delayed detection may result in neurodevelopmental delay due to untreated neonatal hypothyroidism."

Gives both the mechanism of the screening failure and its consequence.

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Pathograph

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

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Phenotypes

11

Digestive 3

Prolonged neonatal jaundice HP:0006579

Show evidence (2 references)

PMID:39875149 SUPPORT Human Clinical

"We discuss a female term neonatal presenting with prolonged unconjugated hyperbilirubinaemia."

The presenting feature in a genetically confirmed patient.

PMID:31703413 SUPPORT BACKGROUND Human Clinical

"Within the first weeks to months of life, affected patients present with severe signs of congenital hypothyroidism, including hypothermia, lethargy, prolonged jaundice, muscle hypotonia, constipation and umbilical hernias."

Lists prolonged jaundice among the neonatal signs. BACKGROUND: an in-vitro paper restating the clinical picture.

Constipation HP:0002019

Show evidence (1 reference)

PMID:31703413 SUPPORT BACKGROUND Human Clinical

"Within the first weeks to months of life, affected patients present with severe signs of congenital hypothyroidism, including hypothermia, lethargy, prolonged jaundice, muscle hypotonia, constipation and umbilical hernias."

Names constipation among the neonatal signs. BACKGROUND for the same reason.

Umbilical hernia HP:0001537

Show evidence (1 reference)

PMID:31703413 SUPPORT BACKGROUND Human Clinical

"Within the first weeks to months of life, affected patients present with severe signs of congenital hypothyroidism, including hypothermia, lethargy, prolonged jaundice, muscle hypotonia, constipation and umbilical hernias."

Names umbilical hernias among the neonatal signs. BACKGROUND for the same reason.

Endocrine 1

Central hypothyroidism OBLIGATE HP:0011787

Show evidence (2 references)

PMID:39875149 SUPPORT Human Clinical

"TSHB gene mutation results in isolated central congenital hypothyroidism (iCCH)."

Names the phenotype as the direct consequence of the TSHB lesion.

PMID:27362444 SUPPORT Human Clinical

"Homozygous mutations in the TSH beta subunit gene (TSHB) result in severe, isolated, central congenital hypothyroidism (CCH)."

Independent statement of the phenotype and of its severity.

Metabolism 1

Hypothermia HP:0002045

Show evidence (1 reference)

PMID:31703413 SUPPORT BACKGROUND Human Clinical

"Within the first weeks to months of life, affected patients present with severe signs of congenital hypothyroidism, including hypothermia, lethargy, prolonged jaundice, muscle hypotonia, constipation and umbilical hernias."

Names hypothermia among the neonatal signs. BACKGROUND because the paper is restating the established clinical picture, not reporting it.

Musculoskeletal 1

Hypotonia HP:0001252

Show evidence (1 reference)

PMID:31703413 SUPPORT BACKGROUND Human Clinical

"Within the first weeks to months of life, affected patients present with severe signs of congenital hypothyroidism, including hypothermia, lethargy, prolonged jaundice, muscle hypotonia, constipation and umbilical hernias."

Muscle hypotonia among the neonatal signs. BACKGROUND for the same reason.

Nervous System 3

Lethargy HP:0001254

Show evidence (1 reference)

PMID:31703413 SUPPORT BACKGROUND Human Clinical

"Within the first weeks to months of life, affected patients present with severe signs of congenital hypothyroidism, including hypothermia, lethargy, prolonged jaundice, muscle hypotonia, constipation and umbilical hernias."

Names lethargy among the neonatal signs. BACKGROUND for the same reason.

Global developmental delay HP:0001263

Show evidence (2 references)

PMID:27362444 SUPPORT Human Clinical

"Neurodevelopmental retardation, following delayed diagnosis and treatment, was present in 3 cases."

The outcome in the late-treated cases.

PMID:27362444 REFUTE Human Clinical

"In contrast, the younger sibling in kindred 1 developed normally following genetic diagnosis and treatment from birth."

A REFUTE item against the claim that this phenotype is an inevitable feature of the disease. Same genotype, same family, different timing of treatment, normal development.

Intellectual disability HP:0001249

Show evidence (1 reference)

PMID:1762181 SUPPORT Human Clinical

"Congenital isolated TSH deficiency is rare disease causing hypothyroidism including cretinism, severe mental and growth retardation."

Severe mental retardation in untreated disease, in the terminology of the source.

Growth 2

Failure to thrive HP:0001508

Show evidence (1 reference)

PMID:1762181 SUPPORT INDIRECT Human Clinical

"Congenital isolated TSH deficiency is rare disease causing hypothyroidism including cretinism, severe mental and growth retardation."

Growth retardation in untreated disease. INDIRECT because the source names growth retardation generally rather than infantile failure to thrive specifically.

Short stature HP:0004322

Show evidence (1 reference)

PMID:1762181 SUPPORT Human Clinical

"Congenital isolated TSH deficiency is rare disease causing hypothyroidism including cretinism, severe mental and growth retardation."

Growth retardation as a consequence of untreated disease.

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Genetic Associations

1

TSHB (Biallelic loss-of-function alleles - frameshift, missense, start-loss and whole-gene deletion)

Gene: TSHB hgnc:12372 relationship_type: CAUSATIVE variant_origin: GERMLINE

Autosomal recessive

Show evidence (3 references)

PMID:31504637 SUPPORT Human Clinical

"Five genes (IGSF1, IRS4, TBL1X, TRHR, and TSHB) responsible for the disease have been identified"

Places TSHB among the established causative genes for congenital isolated TSH deficiency.

PMID:31166470 SUPPORT Human Clinical

"The c.373delT mutation has previously been reported in patients from Brazil, Germany, Belgium, United States, Switzerland, Argentina, France, Portugal, United Kingdom and Ireland."

Documents the geographic spread of the recurrent allele, which is what makes it the first variant to look for.

PMID:27362444 SUPPORT Human Clinical

"In kindreds 2 and 3, the affected individuals were compound heterozygous for TSHB c.373delT and either a 5·4-kB TSHB deletion (kindred 2, c.1-4389_417*195delinsCTCA) or a novel TSHB missense mutation (kindred 3, c.2T>C, p.Met1?)."

Establishes that the allelic spectrum includes a multi-kilobase deletion and a start-loss variant, not only point mutations.

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Medical Actions

1

Levothyroxine Replacement

Action: Pharmacotherapy NCIT:C15986

Agent: levothyroxine CHEBI:18332

Platform: Small molecule

Lifelong levothyroxine, started as early as possible. The drug replaces the missing end-product rather than the missing hormone, so it bypasses the lesion entirely and is effective regardless of which TSHB allele is present. Two things make its use here different from primary hypothyroidism. First, timing dominates outcome: started from birth it averts neurocognitive sequelae even in severe disease, and a 25-year follow-up supports that this holds long term. Second, it cannot be titrated on TSH, because TSH is already inappropriately low and does not respond; dose is guided by free T4 together with clinical assessment.

Mechanism Target:

Systemic Thyroid Hormone Deficiency — Replaces circulating thyroxine directly, restoring peripheral thyroid hormone receptor signalling without repairing anything upstream. The thyroid remains understimulated and the TSH remains low on treatment.

Show evidence (1 reference)

PMID:39875149 SUPPORT DIRECT Human Clinical

"Despite having severe congenital hypothyroidism, timely initiation of levothyroxine averted neurocognitive sequelae."

The clinical outcome of replacing the end-product, followed for 25 years.

Show evidence (2 references)

PMID:39875149 SUPPORT DIRECT Human Clinical

"Early diagnosis and prompt thyroxine initiation are rewarding regardless of the severity of mutation."

States that the benefit does not depend on allele severity, which is the practical point for counselling.

PMID:25248602 SUPPORT DIRECT REVIEW SYNTHESIS Other

"In patients with primary hypothyroidism (PH), L-T4 replacement therapy can safely be adjusted to the individual needs by testing serum thyrotropin (TSH) concentration exclusively."

States the monitoring rule for primary hypothyroidism, which is precisely the rule that does not transfer to this disorder.

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Biochemical Markers

2

Serum Thyrotropin (TSH) (DECREASED)

Pathograph Readouts

Readout Of Failure to Assemble Bioactive TSH Heterodimer Negative Diagnostic

Immunoassay TSH is low, normal or undetectable rather than raised. Note that the assay measures immunoreactive TSH, which is not the same thing as bioactive TSH - a distinction that matters here in both directions, since the p.R75G variant produces the opposite dissociation.

Show evidence (1 reference)

PMID:39875149 SUPPORT Human Clinical

"the history of low T4 and undetectable TSH at diagnosis plus subsequent normal anterior pituitary hormones and normal pituitary on MRI raised suspicion of iCCH"

The measured TSH in a confirmed patient, and the reasoning it supported.

Show evidence (1 reference)

PMID:26416826 SUPPORT REVIEW SYNTHESIS Other

"Since TSH cannot be used as an indicator of euthyroidism, adequacy of treatment can be difficult to monitor due to a paucity of alternative biomarkers."

States the monitoring limitation that makes this marker diagnostically necessary but therapeutically useless here.

Serum Free Thyroxine (Free T4) (DECREASED)

Pathograph Readouts

Readout Of Systemic Thyroid Hormone Deficiency Negative Diagnostic

Low free T4 with a non-elevated TSH is the diagnostic pattern, and free T4 in the mid-to-upper reference range is the treatment target.

Show evidence (1 reference)

PMID:39875149 SUPPORT Human Clinical

"the history of low T4 and undetectable TSH at diagnosis plus subsequent normal anterior pituitary hormones and normal pituitary on MRI raised suspicion of iCCH"

The low T4 measured at diagnosis, alongside the normal remaining pituitary function that makes the deficiency isolated.

Show evidence (1 reference)

PMID:25248602 SUPPORT REVIEW SYNTHESIS Other

"Therefore, L-T4 replacement in CeH should rely on the combined evaluation of several biochemical and clinical parameters in order to overcome the lack of accuracy of the single index."

States that no single biochemical index is adequate for monitoring, which is why free T4 is used with clinical assessment rather than alone.

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Diagnosis

3

Paired Free T4 and TSH Measurement

The diagnosis is made on the pattern, not on either value. A low free T4 with a TSH that is low, normal or undetectable is the signature; either analyte alone is uninformative or actively misleading. In the reported cases the suspicion came from a clinician noticing that thyroid function tests did not fit primary thyroid disease.

thyroid function testing NCIT:C25294

Show evidence (1 reference)

PMID:39875149 SUPPORT Human Clinical

"The diagnosis of hypothyroidism was based on strong clinical suspicion, although her thyroid function tests were not felt to fit with the usual appearance of primary thyroid disease."

Describes exactly how the pattern is recognised in practice, and that it requires a clinician to notice the mismatch.

T4-Based Newborn Screening

The population-level test that determines whether this disease is found in time. A programme measuring T4, such as the Dutch heel-prick screen, detects central congenital hypothyroidism; a programme measuring TSH alone cannot. Under T4-based screening the broader entity appears substantially more common than previously assumed, which is a statement about ascertainment as much as about prevalence.

newborn screening NCIT:C81178

Show evidence (2 references)

PMID:26416826 SUPPORT REVIEW SYNTHESIS Other

"Although uncommon, it may be more prevalent than previously thought, affecting up to 1:16 000 neonates in the Netherlands."

The Dutch T4-based figure, which is the ascertainment argument for T4 screening.

PMID:31166470 REFUTE Human Clinical

"Isolated TSH deficiency is not detected by routine TSH-based neonatal screening, representing a clinical challenge."

A REFUTE item against the claim that routine newborn screening detects this disorder. It does not, where the programme measures TSH.

TSHB Sequencing and Cascade Family Testing

Molecular confirmation, and the route to finding relatives. Because the recurrent frameshift is carried worldwide and because affected siblings may be presymptomatic, identifying the familial allele converts a late diagnosis in the proband into a birth diagnosis for the next child.

targeted gene sequencing and carrier testing NCIT:C15709

Show evidence (2 references)

PMID:31166470 SUPPORT Human Clinical

"Identification of affected and carriers allows the diagnosis, treatment and adequate genetic counseling."

States the purpose of cascade testing in this disorder.

PMID:27362444 SUPPORT Human Clinical

"Accordingly, genetic diagnosis, enabling ascertainment of affected relatives in families, is critical for prompt diagnosis and treatment of the disorder."

Makes the case for genetic diagnosis specifically as a route to finding affected relatives early.

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Prevalence

4

Worldwide

Cases In Literature Ultra Rare

No population estimate exists for the TSHB-caused entity specifically. What is available is a count of reported cases for the commonest allele - 36 at the time of the 2019 functional study - and prevalence figures for the broader category of central congenital hypothyroidism, which are recorded on the separate record below and must not be read as this disorder's rate. No rate is entered on this record.

Show evidence (1 reference)

PMID:31703413 SUPPORT BACKGROUND Human Clinical

"The mutation C105Vfs114X was first described in 1996, and so far 36 cases have been reported"

A literature count for the single commonest pathogenic allele. BACKGROUND: the in-vitro paper is summarising the case literature.

Netherlands, T4-based newborn screening

Birth Prevalence 6.25 per 100,000 live births 1–9 per 100,000 (births)

This is the rate for central congenital hypothyroidism as a whole, not for the TSHB-caused disorder this entry curates, which is a small fraction of it. It is recorded because it is the only ascertainment-based figure available and because it is the number that justifies T4-based screening. Converted from the source's "up to 1:16 000 neonates" (100000/16000 = 6.25). Read it as an upper bound on this disease's birth prevalence, not as an estimate of it.

Show evidence (1 reference)

PMID:26416826 SUPPORT REVIEW SYNTHESIS Other

"Although uncommon, it may be more prevalent than previously thought, affecting up to 1:16 000 neonates in the Netherlands."

The source figure for the rate on this record, stated for central congenital hypothyroidism as a category.

Worldwide, central congenital hypothyroidism as a category

Birth Prevalence 3.3 per 100,000 (3.3–7.7) live births 1–9 per 100,000 (births)

Again a rate for the category, not for the TSHB entity, and recorded for the same reason as the Dutch record above - it is an upper bound on this disease, not an estimate of it. Converted from the source's "1 in 13,000-30,000" (100000/30000 = 3.3 to 100000/13000 = 7.7). The Dutch T4-screening figure recorded separately is 1 in 16,000, which is 6.25 per 100,000 and therefore sits inside this range rather than outside it. The two sources are consistent, and no inference about differential ascertainment can be drawn from comparing them - an earlier version of this note drew one, on the mistaken premise that the range fell below the Dutch figure.

Show evidence (1 reference)

PMID:39913280 SUPPORT REVIEW SYNTHESIS Other

"With an estimated incidence of 1 in 13,000-30,000, central CH is less common than primary CH (incidence 1 in 2000-3000) (6)."

The incidence range for the category, alongside the primary-hypothyroidism comparison that puts it in scale.

Worldwide, relative to primary hypothyroidism

Unknown Rare

A ratio rather than a rate: central hypothyroidism is described as about 1000-fold rarer than primary hypothyroidism. `measure_type` is UNKNOWN because the source states a relative frequency without naming the measure it is relative on, and no rate is entered because a ratio to an unstated denominator is not one.

Show evidence (1 reference)

PMID:25248602 SUPPORT REVIEW SYNTHESIS Other

"CeH is about 1000-fold rarer than PH and raises several challenges for clinicians, mainly because they cannot rely on the systematic use of the reflex TSH strategy for diagnosis or therapy monitoring."

The relative-frequency statement, and the reason it matters clinically.

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Clinical Burden

Variable

Burden here is set almost entirely by time to treatment rather than by genotype, which is unusual enough to be worth stating plainly. Untreated, the disorder produces cretinism with severe intellectual and growth impairment. Treated from birth, outcomes are normal - and the cleanest demonstration is within a single kindred, where three late-diagnosed relatives had neurodevelopmental retardation and the younger sibling diagnosed genetically and treated from birth developed normally. VARIABLE therefore encodes a modifiable variable, not diagnostic uncertainty.

Show evidence (2 references)

PMID:27362444 SUPPORT Human Clinical

"In contrast, the younger sibling in kindred 1 developed normally following genetic diagnosis and treatment from birth."

The within-family contrast that sets the low end of the burden range.

PMID:1762181 SUPPORT Human Clinical

"Congenital isolated TSH deficiency is rare disease causing hypothyroidism including cretinism, severe mental and growth retardation."

The untreated outcome that sets the high end.

{ }

Source YAML

click to show

name: Isolated Thyroid-stimulating Hormone Deficiency
creation_date: "2026-09-21T00:00:00Z"
description: >-
  Congenital central hypothyroidism caused by biallelic loss-of-function variants
  in TSHB, the gene for the beta subunit of thyroid-stimulating hormone. The
  thyroid gland itself is normal; what is missing is the pituitary signal that
  drives it. Because the beta subunit is what makes TSH a thyrotropin rather than
  a generic glycoprotein hormone - the alpha subunit is shared with LH, FSH and
  hCG - losing it means no functional heterodimer can be assembled, the thyroid is
  never stimulated, and circulating free T4 and free T3 fall from birth.

  The defining clinical problem is diagnostic rather than therapeutic. Treatment is
  levothyroxine and, given early enough, it is close to curative: a 25-year
  follow-up of a severely affected patient concluded that timely replacement
  averted neurocognitive sequelae. But the biochemical signature is a low free T4
  beside a TSH that is low, normal or undetectable, and newborn screening
  programmes that measure TSH alone are built to detect the opposite pattern. Such
  a programme cannot see this disease at all, so affected infants present later
  with prolonged jaundice, hypotonia, failure to thrive and oedema, and untreated
  disease ends in irreversible intellectual disability and growth failure. Whether
  a given child is detected depends on which analyte their country screens.
category: Mendelian
parents:
- Congenital Hypothyroidism
- Central Hypothyroidism
disease_term:
  preferred_term: isolated thyroid-stimulating hormone deficiency
  term:
    id: MONDO:0010139
    label: isolated thyroid-stimulating hormone deficiency
mappings:
  mondo_mappings:
  - term:
      id: MONDO:0016410
      label: central congenital hypothyroidism
    mapping_predicate: skos:broadMatch
    mapping_source: MONDO
    mapping_justification: >-
      MONDO:0010139 is a child of MONDO:0016410, which is curated separately as
      kb/disorders/Central_Congenital_Hypothyroidism.yaml. Recorded as broadMatch
      so the relationship between the two entries is queryable from this side
      rather than implicit. Note that broadMatch deliberately does not retire the
      parent concept from the curation queue, which is correct here: this entry
      curates the TSHB entity, not the category.
synonyms:
- isolated TSH deficiency
- i-TSHD
- congenital hypothyroidism, non-goitrous, 4
- TSH deficiency, isolated
- thyrotropin deficiency
- TSHB-related congenital central hypothyroidism
notes: >-
  Entry scope, and the one decision a reader should check first, because the
  neighbouring entry already exists. `kb/disorders/Central_Congenital_Hypothyroidism.yaml`
  curates MONDO:0016410, the wider clinical category, and MONDO makes
  MONDO:0010139 a child of it. That entry already carries a `genetic:` row named
  "TSHB pathogenic variants", so the honest question is whether this should have
  been a `has_subtypes` row there instead of a separate entry.

  It is curated separately, on a mechanistic ground rather than an
  administrative one. The parent entry's pathograph is rooted at a node called
  "Impaired Hypothalamic-Pituitary TSH Drive", and that node is the wrong
  description of this disease. In TSHB deficiency the drive is not impaired: the
  hypothalamus and the thyrotroph work normally, and the hormone they produce
  cannot assemble into a functional heterodimer. The founding report showed
  exactly this - the mutant beta polypeptide is conformationally altered and
  cannot associate with the alpha subunit. Folding TSHB into a regulatory-drive
  node would assert a mechanism that is wrong for it, and the same applies in
  reverse to IGSF1, TBL1X, TRHR and IRS4, each of which does act upstream and each
  of which has its own MONDO term and its own extrathyroidal features
  (macroorchidism for IGSF1, sensorineural hearing loss for TBL1X).

  What the parent entry carries for TSHB today is a gene row with one citation
  and an inheritance block - not a pathograph. The two entries are therefore
  complementary rather than duplicative, and the relationship is now recorded
  explicitly in `mappings.mondo_mappings` as a `skos:broadMatch` to
  MONDO:0016410. The reciprocal gap - the parent entry carries no
  `mappings.mondo_mappings` block at all and does not cite MONDO:0010139 - is
  real and is left for a separate change rather than bundled into a curation PR
  for a different disease; it is recorded in `discussions`.

  This scoping was challenged rather than assumed. The automated second-opinion
  comment on the claim issue (dismech#12392) raised the parent entry and argued
  the subtype case; this note is the answer to it. Worth recording that the
  duplicate preflight for this claim searched `origin/main` for MONDO:0010139 and
  for the label "isolated thyroid-stimulating hormone deficiency" and found
  nothing - it did not search for `TSHB` or for "central congenital
  hypothyroidism", which is how an entry covering the same gene was missed. That
  is the exact failure the `claim-disease` skill warns about when it says the
  claim check cannot see a disease curated under a different term.

  This scoping is not hypothetical bookkeeping. The deep-research report used for
  this entry covers all five genes, and `just preflight-dr` returned WARN on
  exactly this basis, reporting IGSF1 mentioned 33 times against TSHB's 67 and
  warning that the report may mix in a second disease entity. Those sections were
  excluded rather than curated down. Nothing in this entry is sourced from the
  report's IGSF1, TBL1X, TRHR or IRS4 material.

  No `has_subtypes` rows are declared. The reported TSHB allele classes - a
  recurrent frameshift, missense alleles, a start-loss variant and a 5.4-kb
  deletion - all converge on absent or non-functional TSH, so there is no basis
  for splitting.

  Module conformance checked and left unset. `just list-modules` was read and
  `kb/modules/` grepped for `hypothalamic`, `pituitary`, `hormone`, `endocrine`,
  `thyroid` and `receptor signaling`. Nothing covers loss of a pituitary
  trophic hormone, so `conforms_to` is left off rather than forced onto a
  general signalling module.

  No GeneReviews chapter exists for this disorder. Checked offline with
  `just check-genereviews kb/disorders/Isolated_Thyroid-stimulating_Hormone_Deficiency.yaml`
  against the committed Bookshelf index; NO_CHAPTER for GeneReviews.

  Deep-research provenance and what was and was not taken from it.
  `research/Isolated_Thyroid-stimulating_Hormone_Deficiency-deep-research-openscientist.md`
  (provider openscientist, 26 citations). Two things from its own validation output
  were followed up rather than taken at face value:

  First, its reference validation listed `PMID:25248602` as unresolved with 8
  mentions, which under the reference SOP would bar citing it. Re-fetched with
  `just fetch-reference PMID:25248602` on 2026-09-21: it resolves cleanly to
  Persani & Bonomi, "Uncertainties in endocrine substitution therapy for central
  endocrine insufficiencies: hypothyroidism", and contains both sentences the
  report quoted from it. The report's flag was a transport-level lookup failure,
  not a confabulation - which is the ambiguity the validator's own wording warns
  about. It is cited here, and this note records the re-check.

  Second, its term validation reported 8 of 14 checked labels as naming a
  different term. One of those is a substantive error rather than a formatting
  one: the report gives `CL:0000209` for "thyrotrope/thyrotropic cell of pars
  distalis". `CL:0000209` is *taste receptor cell*. The correct term, used in this
  entry, is `CL:0000476` thyrotroph, looked up in `cache/cl/terms.csv`. No CURIE in
  this entry was taken from the report without an independent lookup.

  The report's most valuable single contribution was a negative one and is curated
  in `discussions`: TSHB p.R75G, a founder variant reaching about 4% carrier
  frequency in Bene Israel Indian Jews, does *not* cause this disease. It leaves
  TSH function intact and merely defeats its detection on some immunoassay
  platforms. It was verified directly against PMID:34981755 before being recorded.
references:
- reference: PMID:1762181
  title: "[DNA diagnosis in endocrinological disease--pituitary disease]."
  tags: []
  findings:
  - statement: >-
      The original molecular description: three consanguineous Japanese families
      sharing a missense mutation in exon 2 of the TSH beta-subunit gene, and the
      characterisation of untreated congenital isolated TSH deficiency as causing
      cretinism with severe mental and growth retardation.
- reference: PMID:2792087
  title: "Thyroid-stimulating hormone (TSH) deficiency caused by a single base substitution in the CAGYC region of the beta-subunit."
  tags: []
  findings:
  - statement: >-
      The founding report, and the one that establishes the molecular mechanism
      directly rather than by inference: a single base substitution in the
      conserved CAGYC region of the TSH beta subunit produces a conformationally
      altered polypeptide that cannot associate with the alpha subunit, shown by
      microinjection of the mutated mRNA into Xenopus oocytes.
- reference: PMID:39913280
  title: "Newborn screening for central congenital hypothyroidism: past, present and future."
  tags: []
  findings:
  - statement: >-
      Review of newborn screening for the wider category, giving an incidence
      estimate for central congenital hypothyroidism of 1 in 13,000-30,000 against
      1 in 2,000-3,000 for primary congenital hypothyroidism, and noting that
      central CH is the only pituitary hormone deficiency any newborn screening
      programme detects.
- reference: PMID:31504637
  title: "Genetics of Congenital Isolated TSH Deficiency: Mutation Screening of the Known Causative Genes and a Literature Review."
  tags: []
  findings:
  - statement: >-
      The systematic review of the genetic architecture. Five genes are established
      for congenital isolated TSH deficiency, of which TSHB is the only one acting
      on the hormone itself; in a Japanese cohort of 13, a causative variant was
      found in 46%, none of them in TSHB.
- reference: PMID:27362444
  title: "Molecular spectrum of TSHβ subunit gene defects in central hypothyroidism in the UK and Ireland."
  tags: []
  findings:
  - statement: >-
      The UK/Ireland series, establishing that the TSHB mutational spectrum includes
      structural variation as well as point mutations, and reporting the
      outcome contrast between a sibling treated from birth and late-treated
      relatives.
- reference: PMID:31166470
  title: "A RECURRENT MUTATION IN TSHB GENE UNDERLYING CENTRAL CONGENITAL HYPOTHYROIDISM UNDETECTABLE IN NEONATAL SCREENING."
  tags: []
  findings:
  - statement: >-
      Reports the recurrent c.373delT allele across multiple countries and states
      the screening problem directly: this disorder is not detected by routine
      TSH-based neonatal screening.
- reference: PMID:31703413
  title: "The Pathogenic TSH β-subunit Variant C105Vfs114X Causes a Modified Signaling Profile at TSHR."
  tags: []
  findings:
  - statement: >-
      The functional characterisation of the commonest pathogenic allele at the
      receptor, showing what the mutant beta subunit does to TSHR signalling rather
      than inferring it from the frameshift.
- reference: PMID:39875149
  title: "Central congenital hypothyroidism due to TSHB gene mutation: 25-year follow-up."
  tags: []
  findings:
  - statement: >-
      Long-term outcome in a single patient treated from the neonatal period: severe
      congenital hypothyroidism with neurocognitive sequelae averted by timely
      levothyroxine, and normal remaining anterior pituitary function.
- reference: PMID:26416826
  title: "Recent advances in central congenital hypothyroidism."
  tags: []
  findings:
  - statement: >-
      Review establishing that T4-based newborn screening detects central congenital
      hypothyroidism where TSH-based screening cannot, and that the absence of a
      usable TSH signal makes treatment monitoring difficult.
- reference: PMID:25248602
  title: "Uncertainties in endocrine substitution therapy for central endocrine insufficiencies: hypothyroidism."
  tags: []
  findings:
  - statement: >-
      States the scale of the entity - central hypothyroidism is about 1000-fold
      rarer than primary hypothyroidism - and the monitoring principle that
      levothyroxine dose in central hypothyroidism cannot be titrated on TSH.
- reference: PMID:34981755
  title: "TSHB R75G is a founder variant and prevalent cause of low or undetectable TSH in Indian Jews."
  tags: []
  findings:
  - statement: >-
      Cited for a negative claim. The TSHB p.R75G founder variant, at ~4% carrier
      frequency in Bene Israel Indian Jews, does not impair TSH function; it defeats
      detection on some immunoassays and so mimics a low TSH in euthyroid people.
      It is the principal differential for an unexpectedly low TSH and is not a
      cause of this disease.
inheritance:
- name: Autosomal recessive
  inheritance_term:
    preferred_term: Autosomal recessive inheritance
    term:
      id: HP:0000007
      label: Autosomal recessive inheritance
  description: >-
    Biallelic TSHB variants, homozygous or compound heterozygous. Consanguinity is
    the usual setting for the homozygous cases and was how the disorder was first
    delineated; the recurrent c.373delT allele also appears in compound
    heterozygotes with a second TSHB lesion.
  evidence:
  - reference: PMID:34981755
    reference_title: "TSHB R75G is a founder variant and prevalent cause of low or undetectable TSH in Indian Jews."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: BACKGROUND
    snippet: "Bi-allelic loss-of-function mutations in TSHB, encoding the beta subunit of thyroid-stimulating hormone (TSH), cause congenital hypothyroidism."
    explanation: "States the biallelic requirement. Marked BACKGROUND because this paper's own subject is the non-pathogenic R75G variant; the sentence is its framing of the established disease."
  - reference: PMID:27362444
    reference_title: "Molecular spectrum of TSHβ subunit gene defects in central hypothyroidism in the UK and Ireland."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "the affected individuals were compound heterozygous for TSHB c.373delT and either a 5·4-kB TSHB deletion"
    explanation: "Compound heterozygosity, confirming that two damaged alleles rather than one are needed."
pathophysiology:
- name: Biallelic TSHB Loss of Function
  biological_scale: MOLECULAR
  role: Initiating genetic lesion
  description: >-
    Two damaged TSHB alleles. The reported lesion classes are a recurrent
    frameshift (p.Cys105Valfs*114), missense alleles including the exon-2 change
    that defined the disorder in three consanguineous Japanese families, a
    start-loss allele p.Met1?, and a 5.4-kb whole-gene deletion. Note that the
    recurrent frameshift is cited in the literature under two cDNA numberings,
    c.373delT and c.313delT, depending on whether the signal peptide is counted;
    they are the same allele, and this entry names it at protein level to avoid
    implying they are two.
  genetic_context:
    gene:
      preferred_term: TSHB
      term:
        id: hgnc:12372
        label: TSHB
    variant_origin: GERMLINE
    zygosity: HOMOZYGOUS
    functional_impact_category: LOSS_OF_FUNCTION
    description: >-
      Homozygous in the consanguineous and founder pedigrees; compound
      heterozygous in the UK and Ireland kindreds, where the recurrent frameshift
      was paired with a large deletion or a start-loss allele.
  genes:
  - preferred_term: TSHB
    term:
      id: hgnc:12372
      label: TSHB
  evidence:
  - reference: PMID:27362444
    reference_title: "Molecular spectrum of TSHβ subunit gene defects in central hypothyroidism in the UK and Ireland."
    supports: SUPPORT
    directness: DIRECT
    evidence_source: HUMAN_CLINICAL
    snippet: "Homozygous mutations in the TSH beta subunit gene (TSHB) result in severe, isolated, central congenital hypothyroidism (CCH)."
    explanation: "States the gene-disease relationship and the zygosity requirement."
  - reference: PMID:1762181
    reference_title: "[DNA diagnosis in endocrinological disease--pituitary disease]."
    supports: SUPPORT
    directness: DIRECT
    evidence_source: HUMAN_CLINICAL
    snippet: "They had a same missense mutation in the 2nd exon of the TSH beta-subunit gene"
    explanation: "The founding molecular observation, in three consanguineous Japanese families."
  downstream:
  - target: Failure to Assemble Bioactive TSH Heterodimer
    description: >-
      Without an intact beta subunit the alpha subunit has no thyrotropin-specific
      partner to pair with.
    evidence:
    - reference: PMID:31703413
      reference_title: "The Pathogenic TSH β-subunit Variant C105Vfs114X Causes a Modified Signaling Profile at TSHR."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "The TSHB mutation C105Vfs114X leads to isolated thyroid-stimulating-hormone-(TSH)-deficiency and results in a severe phenotype."
      explanation: "Links the specific allele to hormone deficiency, which is what this edge asserts."
- name: Failure to Assemble Bioactive TSH Heterodimer
  biological_scale: MOLECULAR
  role: Hormone-level lesion
  description: >-
    TSH is a heterodimer of a shared alpha subunit and the TSHB-encoded beta
    subunit; the beta subunit is what confers thyrotropin specificity. The
    frameshift allele has been characterised at the receptor rather than merely
    inferred: the mutant hormone diminishes cAMP signalling at TSHR, and does not
    induce phospholipase C activation at all, while - unexpectedly - leaving MAPK
    signalling comparable to wild type. So the lesion is a selective loss across
    TSHR's signalling arms rather than a uniform silencing of the receptor.
  cell_types:
  - preferred_term: pituitary thyrotroph
    term:
      id: CL:0000476
      label: thyrotroph
  biological_processes:
  - preferred_term: thyroid-stimulating hormone signaling at TSHR
    term:
      id: GO:0038194
      label: thyroid-stimulating hormone signaling pathway
    modifier: DECREASED
  locations:
  - preferred_term: adenohypophysis
    term:
      id: UBERON:0002196
      label: adenohypophysis
  evidence:
  - reference: PMID:31703413
    reference_title: "The Pathogenic TSH β-subunit Variant C105Vfs114X Causes a Modified Signaling Profile at TSHR."
    supports: SUPPORT
    directness: DIRECT
    evidence_source: IN_VITRO
    snippet: "The patient mutation C105Vfs114X and further designed TSH mutants diminished cyclic adenosine monophosphate (cAMP) signaling activity."
    explanation: "Direct receptor-level measurement of what the mutant hormone fails to do."
  - reference: PMID:31703413
    reference_title: "The Pathogenic TSH β-subunit Variant C105Vfs114X Causes a Modified Signaling Profile at TSHR."
    supports: SUPPORT
    directness: DIRECT
    evidence_source: IN_VITRO
    snippet: "Surprisingly, MAPK signaling for all mutants was comparable to WT, while none of the mutants induced PLC activation."
    explanation: "Establishes that the loss is arm-selective, not a global failure of the receptor - which is why the node describes a modified rather than an abolished signal."
  - reference: PMID:2792087
    reference_title: "Thyroid-stimulating hormone (TSH) deficiency caused by a single base substitution in the CAGYC region of the beta-subunit."
    supports: SUPPORT
    directness: DIRECT
    evidence_source: IN_VITRO
    snippet: "Microinjection of the mutated beta mRNAs into Xenopus laevis oocytes led to the formation of conformationally altered beta polypeptides that could not associate with alpha subunits."
    explanation: "The direct demonstration that this node asserts: the mutant beta subunit is misfolded and cannot pair with the alpha subunit, so no heterodimer forms. This is a failure of assembly rather than of production, and it is why the disorder is not a failure of pituitary drive."
  - reference: PMID:2792087
    reference_title: "Thyroid-stimulating hormone (TSH) deficiency caused by a single base substitution in the CAGYC region of the beta-subunit."
    supports: SUPPORT
    directness: DIRECT
    evidence_source: OTHER
    snippet: "The alteration is in the center of the so-called CAGYC region, which consists of an amino acid sequence conserved among all of the known glycoprotein hormone beta subunits."
    explanation: >-
      Locates the founding lesion in a motif conserved across every glycoprotein
      hormone beta subunit, which is why a single substitution there abolishes
      pairing. Graded OTHER rather than HUMAN_CLINICAL because the quoted sentence
      is a comparative-sequence observation across paralogues, not a clinical
      finding in the patients, even though the variant itself was found by
      sequencing them.
  downstream:
  - target: Invisibility to TSH-Based Newborn Screening
    description: >-
      The same absent bioactive heterodimer that fails to stimulate the thyroid is
      also the analyte a TSH-based screening programme measures. A screen looking for
      raised TSH therefore reads normal in exactly the patients who have none, which
      is why the detection failure is a consequence of the molecular lesion rather
      than a separate root.
    evidence:
    - reference: PMID:31166470
      reference_title: "A RECURRENT MUTATION IN TSHB GENE UNDERLYING CENTRAL CONGENITAL HYPOTHYROIDISM UNDETECTABLE IN NEONATAL SCREENING."
      supports: SUPPORT
      directness: DIRECT
      evidence_source: HUMAN_CLINICAL
      snippet: "Isolated TSH deficiency is not detected by routine TSH-based neonatal screening, representing a clinical challenge."
      explanation: "States the screening failure as a property of the TSH deficiency itself."
  - target: Understimulation of the Normal Thyroid Gland
    description: The thyroid is structurally intact but receives no adequate trophic signal.
    evidence:
    - reference: PMID:26416826
      reference_title: "Recent advances in central congenital hypothyroidism."
      supports: SUPPORT
      evidence_source: OTHER
      quote_role: REVIEW_SYNTHESIS
      snippet: "Central congenital hypothyroidism (CCH) is a rare disorder in which inadequate thyroid hormone biosynthesis occurs due to defective stimulation of a normal thyroid gland by thyroid stimulating hormone (TSH)."
      explanation: "States the defining relation: a normal gland, defectively stimulated. Marked REVIEW_SYNTHESIS because the source is a review stating the field's settled definition."
- name: Understimulation of the Normal Thyroid Gland
  biological_scale: TISSUE
  role: Target organ consequence
  description: >-
    Thyroid follicular cells do not receive the cAMP-mediated trophic and secretory
    signal they depend on, so thyroid hormone synthesis and release fall. The gland
    is not goitrous and is not intrinsically abnormal, which is what distinguishes
    this from primary congenital hypothyroidism and gives the disorder its OMIM
    name, congenital non-goitrous hypothyroidism.
  cell_types:
  - preferred_term: thyroid follicular cell
    term:
      id: CL:0002258
      label: thyroid follicular cell
  biological_processes:
  - preferred_term: thyroid hormone generation
    term:
      id: GO:0006590
      label: thyroid hormone generation
    modifier: DECREASED
  locations:
  - preferred_term: thyroid gland
    term:
      id: UBERON:0002046
      label: thyroid gland
  evidence:
  - reference: PMID:26416826
    reference_title: "Recent advances in central congenital hypothyroidism."
    supports: SUPPORT
    directness: DIRECT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: "Central congenital hypothyroidism (CCH) is a rare disorder in which inadequate thyroid hormone biosynthesis occurs due to defective stimulation of a normal thyroid gland by thyroid stimulating hormone (TSH)."
    explanation: "Names both halves of this node: reduced hormone biosynthesis, in a structurally normal gland."
  downstream:
  - target: Systemic Thyroid Hormone Deficiency
    description: Reduced synthesis and secretion lower circulating free T4 and free T3.
    evidence:
    - reference: PMID:39875149
      reference_title: "Central congenital hypothyroidism due to TSHB gene mutation: 25-year follow-up."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "the history of low T4 and undetectable TSH at diagnosis plus subsequent normal anterior pituitary hormones and normal pituitary on MRI raised suspicion of iCCH"
      explanation: "The measured biochemical state in a patient: low T4 with an undetectable rather than raised TSH."
- name: Systemic Thyroid Hormone Deficiency
  biological_scale: ORGANISM
  role: Systemic consequence
  description: >-
    Low circulating free T4 and free T3 from birth, with a TSH that is low, normal
    or undetectable and does not rise. Thyroid hormone is required for central
    nervous system myelination and maturation, for linear growth and for basal
    metabolic rate, so the deficiency is expressed across all three. The severity
    is comparable to athyreosis rather than to a partial biosynthetic defect, which
    was not what the field expected of a TSHB lesion.
  biological_processes:
  - preferred_term: thyroid hormone receptor signaling in peripheral tissues
    term:
      id: GO:0002154
      label: thyroid hormone receptor signaling pathway
    modifier: DECREASED
  evidence:
  - reference: PMID:31703413
    reference_title: "The Pathogenic TSH β-subunit Variant C105Vfs114X Causes a Modified Signaling Profile at TSHR."
    supports: SUPPORT
    directness: DIRECT
    evidence_source: HUMAN_CLINICAL
    quote_role: BACKGROUND
    snippet: "Therefore, patients with a TSHB-gene mutation show a severe phenotype comparable to patients with athyreosis"
    explanation: "Calibrates the severity of the systemic deficiency against a reference condition. BACKGROUND because this in-vitro paper is restating the clinical literature here, not reporting its own patients."
  - reference: PMID:31703413
    reference_title: "The Pathogenic TSH β-subunit Variant C105Vfs114X Causes a Modified Signaling Profile at TSHR."
    supports: SUPPORT
    directness: DIRECT
    evidence_source: HUMAN_CLINICAL
    quote_role: BACKGROUND
    snippet: "Within the first weeks to months of life, affected patients present with severe signs of congenital hypothyroidism, including hypothermia, lethargy, prolonged jaundice, muscle hypotonia, constipation and umbilical hernias."
    explanation: "Enumerates the neonatal systemic manifestations. BACKGROUND for the same reason."
  downstream:
  - target: Central hypothyroidism
    description: The defining biochemical phenotype.
    evidence:
    - reference: PMID:39875149
      reference_title: "Central congenital hypothyroidism due to TSHB gene mutation: 25-year follow-up."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "TSHB gene mutation results in isolated central congenital hypothyroidism (iCCH)."
      explanation: "The direct statement of the disease-defining biochemical state."
  - target: Global developmental delay
    description: >-
      Untreated neonatal thyroid hormone deficiency during the period of CNS
      maturation. Preventable, not inevitable.
    evidence:
    - reference: PMID:27362444
      reference_title: "Molecular spectrum of TSHβ subunit gene defects in central hypothyroidism in the UK and Ireland."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Neurodevelopmental retardation, following delayed diagnosis and treatment, was present in 3 cases."
      explanation: "Attributes the neurodevelopmental outcome specifically to delay in diagnosis and treatment."
  - target: Hypothermia
    description: >-
      A systemic consequence of the thyroid hormone deficit, presenting in the same
      first weeks of life as the other untreated features.
    evidence:
    - reference: PMID:31703413
      reference_title: "The Pathogenic TSH β-subunit Variant C105Vfs114X Causes a Modified Signaling Profile at TSHR."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      quote_role: BACKGROUND
      snippet: "Within the first weeks to months of life, affected patients present with severe signs of congenital hypothyroidism, including hypothermia, lethargy, prolonged jaundice, muscle hypotonia, constipation and umbilical hernias."
      explanation: "Names hypothermia among the neonatal signs. BACKGROUND because the paper is restating the established clinical picture, not reporting it."
  - target: Lethargy
    description: >-
      A systemic consequence of the thyroid hormone deficit, presenting in the same
      first weeks of life as the other untreated features.
    evidence:
    - reference: PMID:31703413
      reference_title: "The Pathogenic TSH β-subunit Variant C105Vfs114X Causes a Modified Signaling Profile at TSHR."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      quote_role: BACKGROUND
      snippet: "Within the first weeks to months of life, affected patients present with severe signs of congenital hypothyroidism, including hypothermia, lethargy, prolonged jaundice, muscle hypotonia, constipation and umbilical hernias."
      explanation: "Names lethargy among the neonatal signs. BACKGROUND for the same reason."
  - target: Constipation
    description: >-
      A systemic consequence of the thyroid hormone deficit, presenting in the same
      first weeks of life as the other untreated features.
    evidence:
    - reference: PMID:31703413
      reference_title: "The Pathogenic TSH β-subunit Variant C105Vfs114X Causes a Modified Signaling Profile at TSHR."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      quote_role: BACKGROUND
      snippet: "Within the first weeks to months of life, affected patients present with severe signs of congenital hypothyroidism, including hypothermia, lethargy, prolonged jaundice, muscle hypotonia, constipation and umbilical hernias."
      explanation: "Names constipation among the neonatal signs. BACKGROUND for the same reason."
  - target: Umbilical hernia
    description: >-
      A systemic consequence of the thyroid hormone deficit, presenting in the same
      first weeks of life as the other untreated features.
    evidence:
    - reference: PMID:31703413
      reference_title: "The Pathogenic TSH β-subunit Variant C105Vfs114X Causes a Modified Signaling Profile at TSHR."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      quote_role: BACKGROUND
      snippet: "Within the first weeks to months of life, affected patients present with severe signs of congenital hypothyroidism, including hypothermia, lethargy, prolonged jaundice, muscle hypotonia, constipation and umbilical hernias."
      explanation: "Names umbilical hernias among the neonatal signs. BACKGROUND for the same reason."
  - target: Hypotonia
    description: >-
      Thyroid hormone is required for normal neuromuscular tone; its systemic deficiency presents in the first weeks of life with muscle hypotonia among the other signs of congenital hypothyroidism.
    evidence:
    - reference: PMID:31703413
      reference_title: "The Pathogenic TSH β-subunit Variant C105Vfs114X Causes a Modified Signaling Profile at TSHR."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      quote_role: BACKGROUND
      snippet: "Within the first weeks to months of life, affected patients present with severe signs of congenital hypothyroidism, including hypothermia, lethargy, prolonged jaundice, muscle hypotonia, constipation and umbilical hernias."
      explanation: "Names muscle hypotonia among the systemic consequences of the hormone deficiency."
  - target: Failure to thrive
    description: >-
      Growth failure follows the systemic hormone deficiency, and is one of the features that brings an unscreened infant to attention.
    evidence:
    - reference: PMID:1762181
      reference_title: "[DNA diagnosis in endocrinological disease--pituitary disease]."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Congenital isolated TSH deficiency is rare disease causing hypothyroidism including cretinism, severe mental and growth retardation."
      explanation: "Names growth retardation as a consequence of isolated TSH deficiency."
  - target: Short stature
    description: >-
      The same growth failure carried forward: untreated thyroid hormone deficiency impairs skeletal growth and final height.
    evidence:
    - reference: PMID:1762181
      reference_title: "[DNA diagnosis in endocrinological disease--pituitary disease]."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Congenital isolated TSH deficiency is rare disease causing hypothyroidism including cretinism, severe mental and growth retardation."
      explanation: "The growth-retardation half of the same sentence, curated here for the stature outcome."
  - target: Intellectual disability
    description: >-
      The irreversible consequence, and the reason detection timing matters: thyroid hormone is required for central nervous system development in the first months of life.
    evidence:
    - reference: PMID:1762181
      reference_title: "[DNA diagnosis in endocrinological disease--pituitary disease]."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Congenital isolated TSH deficiency is rare disease causing hypothyroidism including cretinism, severe mental and growth retardation."
      explanation: "Names severe mental retardation and cretinism as consequences of isolated TSH deficiency."
  - target: Prolonged neonatal jaundice
    description: A common presenting sign, and often the reason the infant is investigated at all.
    evidence:
    - reference: PMID:39875149
      reference_title: "Central congenital hypothyroidism due to TSHB gene mutation: 25-year follow-up."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "We discuss a female term neonatal presenting with prolonged unconjugated hyperbilirubinaemia."
      explanation: "The presenting feature in a genetically confirmed patient."
- name: Invisibility to TSH-Based Newborn Screening
  biological_scale: ORGANISM
  role: Diagnostic-pathway failure, not a biological lesion
  description: >-
    Curated as a node because in this disease the detection pathway determines the
    outcome as directly as the biology does. A TSH-based screening programme looks
    for a raised TSH; here TSH is low or undetectable, so an affected infant screens
    normal. Whether a child is found in the first week of life or months later
    therefore depends on which analyte their country's programme measures - T4-based
    programmes such as the Dutch heel-prick screen detect the condition, TSH-only
    programmes cannot. Everything downstream of this node is preventable.
  evidence:
  - reference: PMID:31166470
    reference_title: "A RECURRENT MUTATION IN TSHB GENE UNDERLYING CENTRAL CONGENITAL HYPOTHYROIDISM UNDETECTABLE IN NEONATAL SCREENING."
    supports: SUPPORT
    directness: DIRECT
    evidence_source: HUMAN_CLINICAL
    snippet: "Isolated TSH deficiency is not detected by routine TSH-based neonatal screening, representing a clinical challenge."
    explanation: "The direct statement of the screening failure."
  - reference: PMID:26416826
    reference_title: "Recent advances in central congenital hypothyroidism."
    supports: SUPPORT
    directness: DIRECT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: "Since TSH is not elevated, CCH will evade diagnosis in primary, TSH-based, CH screening programs and delayed detection may result in neurodevelopmental delay due to untreated neonatal hypothyroidism."
    explanation: "Gives both the mechanism of the screening failure and its consequence."
  downstream:
  - target: Global developmental delay
    description: >-
      The screening failure is upstream of the neurodevelopmental outcome, because
      the outcome is a function of how long the deficiency goes untreated.
    evidence:
    - reference: PMID:27362444
      reference_title: "Molecular spectrum of TSHβ subunit gene defects in central hypothyroidism in the UK and Ireland."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "This entity evades diagnosis in TSH-based congenital hypothyroidism (CH) screening programmes in the UK and Ireland."
      explanation: "Establishes the screening gap in the same series that reports the neurodevelopmental outcomes it leads to."
phenotypes:
- name: Central hypothyroidism
  category: Laboratory
  description: >-
    The defining biochemical state: low free T4 and free T3 with a TSH that is low,
    normal or undetectable and does not rise in response. It is the inappropriate
    normality of the TSH, not its absolute value, that identifies the disorder.
  diagnostic: true
  frequency: OBLIGATE
  phenotype_term:
    preferred_term: Central hypothyroidism
    term:
      id: HP:0011787
      label: Central hypothyroidism
  evidence:
  - reference: PMID:39875149
    reference_title: "Central congenital hypothyroidism due to TSHB gene mutation: 25-year follow-up."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "TSHB gene mutation results in isolated central congenital hypothyroidism (iCCH)."
    explanation: "Names the phenotype as the direct consequence of the TSHB lesion."
  - reference: PMID:27362444
    reference_title: "Molecular spectrum of TSHβ subunit gene defects in central hypothyroidism in the UK and Ireland."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Homozygous mutations in the TSH beta subunit gene (TSHB) result in severe, isolated, central congenital hypothyroidism (CCH)."
    explanation: "Independent statement of the phenotype and of its severity."
- name: Prolonged neonatal jaundice
  category: Clinical
  description: >-
    Prolonged unconjugated hyperbilirubinaemia, a common presenting sign and
    frequently the trigger for investigation in a country whose screen cannot see
    the disease.
  diagnostic: true
  phenotype_term:
    preferred_term: Prolonged neonatal jaundice
    term:
      id: HP:0006579
      label: Prolonged neonatal jaundice
  evidence:
  - reference: PMID:39875149
    reference_title: "Central congenital hypothyroidism due to TSHB gene mutation: 25-year follow-up."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We discuss a female term neonatal presenting with prolonged unconjugated hyperbilirubinaemia."
    explanation: "The presenting feature in a genetically confirmed patient."
  - reference: PMID:31703413
    reference_title: "The Pathogenic TSH β-subunit Variant C105Vfs114X Causes a Modified Signaling Profile at TSHR."
    supports: SUPPORT
    quote_role: BACKGROUND
    evidence_source: HUMAN_CLINICAL
    snippet: "Within the first weeks to months of life, affected patients present with severe signs of congenital hypothyroidism, including hypothermia, lethargy, prolonged jaundice, muscle hypotonia, constipation and umbilical hernias."
    explanation: "Lists prolonged jaundice among the neonatal signs. BACKGROUND: an in-vitro paper restating the clinical picture."
- name: Hypothermia
  category: Clinical
  description: Impaired thermogenesis in the untreated neonate, part of the same first-weeks presentation.
  phenotype_term:
    preferred_term: Hypothermia
    term:
      id: HP:0002045
      label: Hypothermia
  evidence:
  - reference: PMID:31703413
    reference_title: "The Pathogenic TSH β-subunit Variant C105Vfs114X Causes a Modified Signaling Profile at TSHR."
    supports: SUPPORT
    quote_role: BACKGROUND
    evidence_source: HUMAN_CLINICAL
    snippet: "Within the first weeks to months of life, affected patients present with severe signs of congenital hypothyroidism, including hypothermia, lethargy, prolonged jaundice, muscle hypotonia, constipation and umbilical hernias."
    explanation: "Names hypothermia among the neonatal signs. BACKGROUND because the paper is restating the established clinical picture, not reporting it."
- name: Lethargy
  category: Clinical
  description: Reduced arousal and activity in the untreated neonate.
  phenotype_term:
    preferred_term: Lethargy
    term:
      id: HP:0001254
      label: Lethargy
  evidence:
  - reference: PMID:31703413
    reference_title: "The Pathogenic TSH β-subunit Variant C105Vfs114X Causes a Modified Signaling Profile at TSHR."
    supports: SUPPORT
    quote_role: BACKGROUND
    evidence_source: HUMAN_CLINICAL
    snippet: "Within the first weeks to months of life, affected patients present with severe signs of congenital hypothyroidism, including hypothermia, lethargy, prolonged jaundice, muscle hypotonia, constipation and umbilical hernias."
    explanation: "Names lethargy among the neonatal signs. BACKGROUND for the same reason."
- name: Constipation
  category: Clinical
  description: Slowed gut motility, a standard consequence of thyroid hormone deficiency.
  phenotype_term:
    preferred_term: Constipation
    term:
      id: HP:0002019
      label: Constipation
  evidence:
  - reference: PMID:31703413
    reference_title: "The Pathogenic TSH β-subunit Variant C105Vfs114X Causes a Modified Signaling Profile at TSHR."
    supports: SUPPORT
    quote_role: BACKGROUND
    evidence_source: HUMAN_CLINICAL
    snippet: "Within the first weeks to months of life, affected patients present with severe signs of congenital hypothyroidism, including hypothermia, lethargy, prolonged jaundice, muscle hypotonia, constipation and umbilical hernias."
    explanation: "Names constipation among the neonatal signs. BACKGROUND for the same reason."
- name: Umbilical hernia
  category: Clinical
  description: Delayed closure of the umbilical ring, a recognised sign of congenital hypothyroidism.
  phenotype_term:
    preferred_term: Umbilical hernia
    term:
      id: HP:0001537
      label: Umbilical hernia
  evidence:
  - reference: PMID:31703413
    reference_title: "The Pathogenic TSH β-subunit Variant C105Vfs114X Causes a Modified Signaling Profile at TSHR."
    supports: SUPPORT
    quote_role: BACKGROUND
    evidence_source: HUMAN_CLINICAL
    snippet: "Within the first weeks to months of life, affected patients present with severe signs of congenital hypothyroidism, including hypothermia, lethargy, prolonged jaundice, muscle hypotonia, constipation and umbilical hernias."
    explanation: "Names umbilical hernias among the neonatal signs. BACKGROUND for the same reason."
- name: Hypotonia
  category: Clinical
  description: Muscle hypotonia in the neonatal period, part of the untreated hypothyroid presentation.
  phenotype_term:
    preferred_term: Hypotonia
    term:
      id: HP:0001252
      label: Hypotonia
  evidence:
  - reference: PMID:31703413
    reference_title: "The Pathogenic TSH β-subunit Variant C105Vfs114X Causes a Modified Signaling Profile at TSHR."
    supports: SUPPORT
    quote_role: BACKGROUND
    evidence_source: HUMAN_CLINICAL
    snippet: "Within the first weeks to months of life, affected patients present with severe signs of congenital hypothyroidism, including hypothermia, lethargy, prolonged jaundice, muscle hypotonia, constipation and umbilical hernias."
    explanation: "Muscle hypotonia among the neonatal signs. BACKGROUND for the same reason."
- name: Global developmental delay
  category: Clinical
  description: >-
    Neurodevelopmental impairment from untreated neonatal thyroid hormone
    deficiency. Curated with its preventability, because the contrast is internal
    to a single kindred: three late-diagnosed cases had neurodevelopmental
    retardation while the younger sibling treated from birth developed normally.
  phenotype_term:
    preferred_term: Global developmental delay
    term:
      id: HP:0001263
      label: Global developmental delay
  evidence:
  - reference: PMID:27362444
    reference_title: "Molecular spectrum of TSHβ subunit gene defects in central hypothyroidism in the UK and Ireland."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Neurodevelopmental retardation, following delayed diagnosis and treatment, was present in 3 cases."
    explanation: "The outcome in the late-treated cases."
  - reference: PMID:27362444
    reference_title: "Molecular spectrum of TSHβ subunit gene defects in central hypothyroidism in the UK and Ireland."
    supports: REFUTE
    evidence_source: HUMAN_CLINICAL
    snippet: "In contrast, the younger sibling in kindred 1 developed normally following genetic diagnosis and treatment from birth."
    explanation: "A REFUTE item against the claim that this phenotype is an inevitable feature of the disease. Same genotype, same family, different timing of treatment, normal development."
- name: Failure to thrive
  category: Clinical
  description: Poor weight gain in infancy when the diagnosis is delayed.
  phenotype_term:
    preferred_term: Failure to thrive
    term:
      id: HP:0001508
      label: Failure to thrive
  evidence:
  - reference: PMID:1762181
    reference_title: "[DNA diagnosis in endocrinological disease--pituitary disease]."
    supports: SUPPORT
    directness: INDIRECT
    evidence_source: HUMAN_CLINICAL
    snippet: "Congenital isolated TSH deficiency is rare disease causing hypothyroidism including cretinism, severe mental and growth retardation."
    explanation: "Growth retardation in untreated disease. INDIRECT because the source names growth retardation generally rather than infantile failure to thrive specifically."
- name: Short stature
  category: Clinical
  description: Growth failure in untreated or inadequately treated disease.
  phenotype_term:
    preferred_term: Short stature
    term:
      id: HP:0004322
      label: Short stature
  evidence:
  - reference: PMID:1762181
    reference_title: "[DNA diagnosis in endocrinological disease--pituitary disease]."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Congenital isolated TSH deficiency is rare disease causing hypothyroidism including cretinism, severe mental and growth retardation."
    explanation: "Growth retardation as a consequence of untreated disease."
- name: Intellectual disability
  category: Clinical
  description: >-
    The severe end of the untreated neurodevelopmental outcome, described in the
    older literature as cretinism. Preventable by early replacement.
  phenotype_term:
    preferred_term: Intellectual disability
    term:
      id: HP:0001249
      label: Intellectual disability
  evidence:
  - reference: PMID:1762181
    reference_title: "[DNA diagnosis in endocrinological disease--pituitary disease]."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Congenital isolated TSH deficiency is rare disease causing hypothyroidism including cretinism, severe mental and growth retardation."
    explanation: "Severe mental retardation in untreated disease, in the terminology of the source."
biochemical:
- name: Serum Thyrotropin (TSH)
  presence: DECREASED
  notes: >-
    The single most important thing about this marker in this disease is that its
    value is not interpretable on its own. A low or undetectable TSH is the normal
    reading in a healthy person and the diagnostic reading here; only the
    combination with a low free T4 makes it abnormal. It also cannot be used to
    monitor treatment, for the same reason. No numeric reference interval is
    recorded: none of the sources cited here states one, and the conventional adult
    interval is assay-dependent. It is left out rather than attributed to a source
    that does not contain it.
  biomarker_term:
    preferred_term: Thyrotropin
    term:
      id: LOINC:3016-3
      label: Thyrotropin [Units/volume] in Serum or Plasma
  readouts:
  - target: Failure to Assemble Bioactive TSH Heterodimer
    relationship: READOUT_OF
    direction: NEGATIVE
    endpoint_context: DIAGNOSTIC
    interpretation: >-
      Immunoassay TSH is low, normal or undetectable rather than raised. Note that
      the assay measures immunoreactive TSH, which is not the same thing as
      bioactive TSH - a distinction that matters here in both directions, since the
      p.R75G variant produces the opposite dissociation.
    evidence:
    - reference: PMID:39875149
      reference_title: "Central congenital hypothyroidism due to TSHB gene mutation: 25-year follow-up."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "the history of low T4 and undetectable TSH at diagnosis plus subsequent normal anterior pituitary hormones and normal pituitary on MRI raised suspicion of iCCH"
      explanation: "The measured TSH in a confirmed patient, and the reasoning it supported."
  evidence:
  - reference: PMID:26416826
    reference_title: "Recent advances in central congenital hypothyroidism."
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: "Since TSH cannot be used as an indicator of euthyroidism, adequacy of treatment can be difficult to monitor due to a paucity of alternative biomarkers."
    explanation: "States the monitoring limitation that makes this marker diagnostically necessary but therapeutically useless here."
- name: Serum Free Thyroxine (Free T4)
  presence: DECREASED
  notes: >-
    Free T4 is the analyte that both detects the disease and monitors its
    treatment, which is unusual - in primary hypothyroidism TSH does both. No
    numeric reference interval is recorded here: the sources cited state the
    direction of change but no interval, and rather than import a conventional
    adult band into a congenital disorder whose age-specific intervals differ
    substantially, the slot is left empty. The convention of recording a
    conventional laboratory interval in `notes` rather than attributing it to a
    citation, as `Generalized_Resistance_to_Thyroid_Hormone` does, would be
    available if an age-appropriate band were needed.
  biomarker_term:
    preferred_term: Free thyroxine
    term:
      id: LOINC:14920-3
      label: Thyroxine (T4) free [Moles/volume] in Serum or Plasma
  readouts:
  - target: Systemic Thyroid Hormone Deficiency
    relationship: READOUT_OF
    direction: NEGATIVE
    endpoint_context: DIAGNOSTIC
    interpretation: >-
      Low free T4 with a non-elevated TSH is the diagnostic pattern, and free T4 in
      the mid-to-upper reference range is the treatment target.
    evidence:
    - reference: PMID:39875149
      reference_title: "Central congenital hypothyroidism due to TSHB gene mutation: 25-year follow-up."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "the history of low T4 and undetectable TSH at diagnosis plus subsequent normal anterior pituitary hormones and normal pituitary on MRI raised suspicion of iCCH"
      explanation: "The low T4 measured at diagnosis, alongside the normal remaining pituitary function that makes the deficiency isolated."
  evidence:
  - reference: PMID:25248602
    reference_title: "Uncertainties in endocrine substitution therapy for central endocrine insufficiencies: hypothyroidism."
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: "Therefore, L-T4 replacement in CeH should rely on the combined evaluation of several biochemical and clinical parameters in order to overcome the lack of accuracy of the single index."
    explanation: "States that no single biochemical index is adequate for monitoring, which is why free T4 is used with clinical assessment rather than alone."
genetic:
- name: TSHB
  gene_term:
    preferred_term: TSHB
    term:
      id: hgnc:12372
      label: TSHB
  relationship_type: CAUSATIVE
  variant_origin: GERMLINE
  association: Biallelic loss-of-function alleles - frameshift, missense, start-loss and whole-gene deletion
  presence: Positive
  inheritance:
  - name: Autosomal recessive
    inheritance_term:
      preferred_term: Autosomal recessive inheritance
      term:
        id: HP:0000007
        label: Autosomal recessive inheritance
  notes: >-
    A caution that belongs on this row rather than anywhere else: not every TSHB
    variant found in a person with a low TSH is causal. The p.R75G allele, at about
    4% carrier frequency in Bene Israel Indian Jews and on a shared haplotype with
    South Asian populations, leaves TSH function intact and only defeats its
    detection on some immunoassay platforms. Carriers are euthyroid and have been
    misdiagnosed with hyperthyroidism. A TSHB variant in a patient with a low TSH
    but a normal free T4 is much more likely to be this than to be this disease.
    See `discussions`.
  evidence:
  - reference: PMID:31504637
    reference_title: "Genetics of Congenital Isolated TSH Deficiency: Mutation Screening of the Known Causative Genes and a Literature Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Five genes (IGSF1, IRS4, TBL1X, TRHR, and TSHB) responsible for the disease have been identified"
    explanation: "Places TSHB among the established causative genes for congenital isolated TSH deficiency."
  - reference: PMID:31166470
    reference_title: "A RECURRENT MUTATION IN TSHB GENE UNDERLYING CENTRAL CONGENITAL HYPOTHYROIDISM UNDETECTABLE IN NEONATAL SCREENING."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The c.373delT mutation has previously been reported in patients from Brazil, Germany, Belgium, United States, Switzerland, Argentina, France, Portugal, United Kingdom and Ireland."
    explanation: "Documents the geographic spread of the recurrent allele, which is what makes it the first variant to look for."
  - reference: PMID:27362444
    reference_title: "Molecular spectrum of TSHβ subunit gene defects in central hypothyroidism in the UK and Ireland."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In kindreds 2 and 3, the affected individuals were compound heterozygous for TSHB c.373delT and either a 5·4-kB TSHB deletion (kindred 2, c.1-4389_417*195delinsCTCA) or a novel TSHB missense mutation (kindred 3, c.2T>C, p.Met1?)."
    explanation: "Establishes that the allelic spectrum includes a multi-kilobase deletion and a start-loss variant, not only point mutations."
diagnosis:
- name: Paired Free T4 and TSH Measurement
  description: >-
    The diagnosis is made on the pattern, not on either value. A low free T4 with a
    TSH that is low, normal or undetectable is the signature; either analyte alone
    is uninformative or actively misleading. In the reported cases the suspicion
    came from a clinician noticing that thyroid function tests did not fit primary
    thyroid disease.
  diagnosis_term:
    preferred_term: thyroid function testing
    term:
      id: NCIT:C25294
      label: Laboratory Procedure
  evidence:
  - reference: PMID:39875149
    reference_title: "Central congenital hypothyroidism due to TSHB gene mutation: 25-year follow-up."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The diagnosis of hypothyroidism was based on strong clinical suspicion, although her thyroid function tests were not felt to fit with the usual appearance of primary thyroid disease."
    explanation: "Describes exactly how the pattern is recognised in practice, and that it requires a clinician to notice the mismatch."
- name: T4-Based Newborn Screening
  description: >-
    The population-level test that determines whether this disease is found in time.
    A programme measuring T4, such as the Dutch heel-prick screen, detects central
    congenital hypothyroidism; a programme measuring TSH alone cannot. Under
    T4-based screening the broader entity appears substantially more common than
    previously assumed, which is a statement about ascertainment as much as about
    prevalence.
  diagnosis_term:
    preferred_term: newborn screening
    term:
      id: NCIT:C81178
      label: Newborn Screening
  evidence:
  - reference: PMID:26416826
    reference_title: "Recent advances in central congenital hypothyroidism."
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: "Although uncommon, it may be more prevalent than previously thought, affecting up to 1:16 000 neonates in the Netherlands."
    explanation: "The Dutch T4-based figure, which is the ascertainment argument for T4 screening."
  - reference: PMID:31166470
    reference_title: "A RECURRENT MUTATION IN TSHB GENE UNDERLYING CENTRAL CONGENITAL HYPOTHYROIDISM UNDETECTABLE IN NEONATAL SCREENING."
    supports: REFUTE
    evidence_source: HUMAN_CLINICAL
    snippet: "Isolated TSH deficiency is not detected by routine TSH-based neonatal screening, representing a clinical challenge."
    explanation: "A REFUTE item against the claim that routine newborn screening detects this disorder. It does not, where the programme measures TSH."
- name: TSHB Sequencing and Cascade Family Testing
  description: >-
    Molecular confirmation, and the route to finding relatives. Because the
    recurrent frameshift is carried worldwide and because affected siblings may be
    presymptomatic, identifying the familial allele converts a late diagnosis in the
    proband into a birth diagnosis for the next child.
  diagnosis_term:
    preferred_term: targeted gene sequencing and carrier testing
    term:
      id: NCIT:C15709
      label: Genetic Testing
  evidence:
  - reference: PMID:31166470
    reference_title: "A RECURRENT MUTATION IN TSHB GENE UNDERLYING CENTRAL CONGENITAL HYPOTHYROIDISM UNDETECTABLE IN NEONATAL SCREENING."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Identification of affected and carriers allows the diagnosis, treatment and adequate genetic counseling."
    explanation: "States the purpose of cascade testing in this disorder."
  - reference: PMID:27362444
    reference_title: "Molecular spectrum of TSHβ subunit gene defects in central hypothyroidism in the UK and Ireland."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Accordingly, genetic diagnosis, enabling ascertainment of affected relatives in families, is critical for prompt diagnosis and treatment of the disorder."
    explanation: "Makes the case for genetic diagnosis specifically as a route to finding affected relatives early."
prevalence:
- population: Worldwide
  measure_type: CASES_IN_LITERATURE
  prevalence_class: ULTRA_RARE
  notes: >-
    No population estimate exists for the TSHB-caused entity specifically. What is
    available is a count of reported cases for the commonest allele - 36 at the
    time of the 2019 functional study - and prevalence figures for the broader
    category of central congenital hypothyroidism, which are recorded on the
    separate record below and must not be read as this disorder's rate. No rate is
    entered on this record.
  evidence:
  - reference: PMID:31703413
    reference_title: "The Pathogenic TSH β-subunit Variant C105Vfs114X Causes a Modified Signaling Profile at TSHR."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: BACKGROUND
    snippet: "The mutation C105Vfs114X was first described in 1996, and so far 36 cases have been reported"
    explanation: "A literature count for the single commonest pathogenic allele. BACKGROUND: the in-vitro paper is summarising the case literature."
- population: Netherlands, T4-based newborn screening
  measure_type: BIRTH_PREVALENCE
  prevalence_class: BAND_1_9_PER_100000
  rate_per_100000: 6.25
  rate_denominator: LIVE_BIRTHS
  notes: >-
    This is the rate for central congenital hypothyroidism as a whole, not for the
    TSHB-caused disorder this entry curates, which is a small fraction of it. It is
    recorded because it is the only ascertainment-based figure available and because
    it is the number that justifies T4-based screening. Converted from the source's
    "up to 1:16 000 neonates" (100000/16000 = 6.25). Read it as an upper bound on
    this disease's birth prevalence, not as an estimate of it.
  evidence:
  - reference: PMID:26416826
    reference_title: "Recent advances in central congenital hypothyroidism."
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: "Although uncommon, it may be more prevalent than previously thought, affecting up to 1:16 000 neonates in the Netherlands."
    explanation: "The source figure for the rate on this record, stated for central congenital hypothyroidism as a category."
- population: Worldwide, central congenital hypothyroidism as a category
  measure_type: BIRTH_PREVALENCE
  prevalence_class: BAND_1_9_PER_100000
  rate_per_100000: 3.3
  rate_low: 3.3
  rate_high: 7.7
  rate_denominator: LIVE_BIRTHS
  notes: >-
    Again a rate for the category, not for the TSHB entity, and recorded for the
    same reason as the Dutch record above - it is an upper bound on this disease,
    not an estimate of it. Converted from the source's "1 in 13,000-30,000"
    (100000/30000 = 3.3 to 100000/13000 = 7.7). The Dutch T4-screening figure
    recorded separately is 1 in 16,000, which is 6.25 per 100,000 and therefore sits
    inside this range rather than outside it. The two sources are consistent, and no
    inference about differential ascertainment can be drawn from comparing them - an
    earlier version of this note drew one, on the mistaken premise that the range
    fell below the Dutch figure.
  evidence:
  - reference: PMID:39913280
    reference_title: "Newborn screening for central congenital hypothyroidism: past, present and future."
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: "With an estimated incidence of 1 in 13,000-30,000, central CH is less common than primary CH (incidence 1 in 2000-3000) (6)."
    explanation: "The incidence range for the category, alongside the primary-hypothyroidism comparison that puts it in scale."
- population: Worldwide, relative to primary hypothyroidism
  measure_type: UNKNOWN
  prevalence_class: RARE
  notes: >-
    A ratio rather than a rate: central hypothyroidism is described as about
    1000-fold rarer than primary hypothyroidism. `measure_type` is UNKNOWN because
    the source states a relative frequency without naming the measure it is
    relative on, and no rate is entered because a ratio to an unstated denominator
    is not one.
  evidence:
  - reference: PMID:25248602
    reference_title: "Uncertainties in endocrine substitution therapy for central endocrine insufficiencies: hypothyroidism."
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: "CeH is about 1000-fold rarer than PH and raises several challenges for clinicians, mainly because they cannot rely on the systematic use of the reflex TSH strategy for diagnosis or therapy monitoring."
    explanation: "The relative-frequency statement, and the reason it matters clinically."
clinical_burden:
  burden_level: VARIABLE
  rationale: >-
    Burden here is set almost entirely by time to treatment rather than by
    genotype, which is unusual enough to be worth stating plainly. Untreated, the
    disorder produces cretinism with severe intellectual and growth impairment.
    Treated from birth, outcomes are normal - and the cleanest demonstration is
    within a single kindred, where three late-diagnosed relatives had
    neurodevelopmental retardation and the younger sibling diagnosed genetically and
    treated from birth developed normally. VARIABLE therefore encodes a modifiable
    variable, not diagnostic uncertainty.
  evidence:
  - reference: PMID:27362444
    reference_title: "Molecular spectrum of TSHβ subunit gene defects in central hypothyroidism in the UK and Ireland."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In contrast, the younger sibling in kindred 1 developed normally following genetic diagnosis and treatment from birth."
    explanation: "The within-family contrast that sets the low end of the burden range."
  - reference: PMID:1762181
    reference_title: "[DNA diagnosis in endocrinological disease--pituitary disease]."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Congenital isolated TSH deficiency is rare disease causing hypothyroidism including cretinism, severe mental and growth retardation."
    explanation: "The untreated outcome that sets the high end."
treatments:
- name: Levothyroxine Replacement
  description: >-
    Lifelong levothyroxine, started as early as possible. The drug replaces the
    missing end-product rather than the missing hormone, so it bypasses the lesion
    entirely and is effective regardless of which TSHB allele is present. Two things
    make its use here different from primary hypothyroidism. First, timing dominates
    outcome: started from birth it averts neurocognitive sequelae even in severe
    disease, and a 25-year follow-up supports that this holds long term. Second, it
    cannot be titrated on TSH, because TSH is already inappropriately low and does
    not respond; dose is guided by free T4 together with clinical assessment.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: levothyroxine
      term:
        id: CHEBI:18332
        label: L-thyroxine
  target_mechanisms:
  - target: Systemic Thyroid Hormone Deficiency
    description: >-
      Replaces circulating thyroxine directly, restoring peripheral thyroid hormone
      receptor signalling without repairing anything upstream. The thyroid remains
      understimulated and the TSH remains low on treatment.
    evidence:
    - reference: PMID:39875149
      reference_title: "Central congenital hypothyroidism due to TSHB gene mutation: 25-year follow-up."
      supports: SUPPORT
      directness: DIRECT
      evidence_source: HUMAN_CLINICAL
      snippet: "Despite having severe congenital hypothyroidism, timely initiation of levothyroxine averted neurocognitive sequelae."
      explanation: "The clinical outcome of replacing the end-product, followed for 25 years."
  evidence:
  - reference: PMID:39875149
    reference_title: "Central congenital hypothyroidism due to TSHB gene mutation: 25-year follow-up."
    supports: SUPPORT
    directness: DIRECT
    evidence_source: HUMAN_CLINICAL
    snippet: "Early diagnosis and prompt thyroxine initiation are rewarding regardless of the severity of mutation."
    explanation: "States that the benefit does not depend on allele severity, which is the practical point for counselling."
  - reference: PMID:25248602
    reference_title: "Uncertainties in endocrine substitution therapy for central endocrine insufficiencies: hypothyroidism."
    supports: SUPPORT
    directness: DIRECT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: "In patients with primary hypothyroidism (PH), L-T4 replacement therapy can safely be adjusted to the individual needs by testing serum thyrotropin (TSH) concentration exclusively."
    explanation: "States the monitoring rule for primary hypothyroidism, which is precisely the rule that does not transfer to this disorder."
discussions:
- discussion_id: tshb_r75g_assay_interference_not_disease
  status: OPEN
  kind: INTERPRETATION
  attaches_to:
  - genetic#TSHB
  - biochemical#Serum Thyrotropin (TSH)
  prompt: >-
    A TSHB variant in a person with a low or undetectable TSH is not necessarily a
    cause of this disease. How should p.R75G be distinguished from a pathogenic
    TSHB allele?
  rationale: >-
    The p.R75G variant is common - about 4% carrier frequency in Bene Israel Indian
    Jews, on a haplotype shared with South Asian populations - and does not impair
    TSH function. What it does is defeat detection of TSH on some immunoassay
    platforms, so carriers who are clinically euthyroid appear to have a low or
    undetectable TSH and have been diagnosed with hyperthyroidism in error. It is
    the mirror image of this disease: the same gene, a low measured TSH, and the
    opposite clinical meaning.

    The discriminator is the free T4. In this disease free T4 is low; in R75G
    carriers it is normal and the patient is euthyroid. The platform matters too -
    the discrepancy is assay-dependent, so re-measuring on a different platform is
    informative.

    Recorded as an interpretation question rather than a knowledge gap because the
    biology is settled; what is unsettled is how reliably it is applied at the
    bench. This entry's own curation nearly got it wrong: the variant reads in a
    title search as a founder pathogenic allele, and it took reading the abstract to
    see that the paper is about euthyroid people.
  evidence:
  - reference: PMID:34981755
    reference_title: "TSHB R75G is a founder variant and prevalent cause of low or undetectable TSH in Indian Jews."
    supports: REFUTE
    directness: DIRECT
    evidence_source: HUMAN_CLINICAL
    snippet: "Homozygosity for the TSHB p.R75G variant, previously described in South Asian individuals, does not alter TSH function but abrogates its detection by some immune detection-based platforms, leading to erroneous diagnosis of hyperthyroidism."
    explanation: "A REFUTE item against treating p.R75G as a cause of this disease. The variant is explicitly stated not to alter TSH function."
  - reference: PMID:34981755
    reference_title: "TSHB R75G is a founder variant and prevalent cause of low or undetectable TSH in Indian Jews."
    supports: SUPPORT
    directness: DIRECT
    evidence_source: HUMAN_CLINICAL
    snippet: "Extremely high carrier rate of p.R75G TSHB in Bene Israel Indian Jews (~4%) was observed."
    explanation: "The carrier frequency, which is what makes this a practical differential rather than a curiosity."
- discussion_id: tshb_screening_analyte_determines_outcome
  status: OPEN
  kind: KNOWLEDGE_GAP
  attaches_to:
  - pathophysiology#Invisibility to TSH-Based Newborn Screening
  prompt: >-
    How many cases of TSHB-related congenital central hypothyroidism are missed by
    TSH-only newborn screening, and what is the neurodevelopmental cost?
  rationale: >-
    The disorder is preventable and the intervention is cheap, so the number that
    matters is how many children are not found. It cannot be read off the
    literature: the Dutch T4-based figure of up to 1:16 000 is for central
    congenital hypothyroidism as a whole, the TSHB share of that is unquantified,
    and the countries where the miss occurs are by construction the ones with no
    denominator. The case series report late diagnoses at five months, at twelve
    years and after neurodevelopmental damage had occurred, but a case series cannot
    give a rate.

    This is a knowledge gap with an unusual property: closing it would not change
    what we know about the biology at all, and would change practice immediately.
- discussion_id: tshb_entity_boundary_versus_other_cch_genes
  status: OPEN
  kind: CURATION_TODO
  attaches_to:
  - disease#Isolated Thyroid-stimulating Hormone Deficiency
  prompt: >-
    Should IGSF1, TBL1X, TRHR and IRS4 central hypothyroidism be curated as separate
    dismech entries, and should a grouping hold them together with this one?
  rationale: >-
    Clinically these five are one differential - a child with a low free T4 and a
    non-elevated TSH - and the published reviews treat them as one entity.
    Mechanistically they are not one thing: TSHB removes the hormone, while IGSF1,
    TBL1X, TRHR and IRS4 act on the regulatory machinery upstream of it, and each
    carries extrathyroidal features the others do not. This entry therefore curates
    only the TSHB entity.

    Two concrete follow-ups, neither actioned here because both change a file this
    curation PR has no business touching:

    1. `kb/disorders/Central_Congenital_Hypothyroidism.yaml` (MONDO:0016410)
       carries no `mappings.mondo_mappings` block at all and does not cite
       MONDO:0010139. This entry now records the relationship from its own side as
       a `skos:broadMatch`, but the parent does not record it reciprocally, so a
       reader arriving at the parent has no signal that the TSHB entity is curated
       separately. Its "TSHB pathogenic variants" genetic row is the obvious place
       for a cross-reference.
    2. IGSF1, TBL1X, TRHR and IRS4 each have their own MONDO term and none is
       curated as a dismech entry. Once two or more exist, a `kb/groupings/` record
       over the clinical differential would capture it without collapsing the
       mechanisms, which is what a grouping is for. A grouping built now would have
       one disease member and would encode this entry rather than the category.

    Raised by the automated second-opinion comment on dismech#12392, which found
    the parent entry and argued the subtype case. The scope note above is the
    answer; these are the parts of its argument that stand.

📚

References & Deep Research

References

11

PMID:1762181

[DNA diagnosis in endocrinological disease--pituitary disease].

1 finding

The original molecular description: three consanguineous Japanese families sharing a missense mutation in exon 2 of the TSH beta-subunit gene, and the characterisation of untreated congenital isolated TSH deficiency as causing cretinism with severe mental and growth retardation.

PMID:2792087

Thyroid-stimulating hormone (TSH) deficiency caused by a single base substitution in the CAGYC region of the beta-subunit.

1 finding

The founding report, and the one that establishes the molecular mechanism directly rather than by inference: a single base substitution in the conserved CAGYC region of the TSH beta subunit produces a conformationally altered polypeptide that cannot associate with the alpha subunit, shown by microinjection of the mutated mRNA into Xenopus oocytes.

PMID:39913280

Newborn screening for central congenital hypothyroidism: past, present and future.

1 finding

Review of newborn screening for the wider category, giving an incidence estimate for central congenital hypothyroidism of 1 in 13,000-30,000 against 1 in 2,000-3,000 for primary congenital hypothyroidism, and noting that central CH is the only pituitary hormone deficiency any newborn screening programme detects.

PMID:31504637

Genetics of Congenital Isolated TSH Deficiency: Mutation Screening of the Known Causative Genes and a Literature Review.

1 finding

The systematic review of the genetic architecture. Five genes are established for congenital isolated TSH deficiency, of which TSHB is the only one acting on the hormone itself; in a Japanese cohort of 13, a causative variant was found in 46%, none of them in TSHB.

PMID:27362444

Molecular spectrum of TSHβ subunit gene defects in central hypothyroidism in the UK and Ireland.

1 finding

The UK/Ireland series, establishing that the TSHB mutational spectrum includes structural variation as well as point mutations, and reporting the outcome contrast between a sibling treated from birth and late-treated relatives.

PMID:31166470

A RECURRENT MUTATION IN TSHB GENE UNDERLYING CENTRAL CONGENITAL HYPOTHYROIDISM UNDETECTABLE IN NEONATAL SCREENING.

1 finding

Reports the recurrent c.373delT allele across multiple countries and states the screening problem directly: this disorder is not detected by routine TSH-based neonatal screening.

PMID:31703413

The Pathogenic TSH β-subunit Variant C105Vfs114X Causes a Modified Signaling Profile at TSHR.

1 finding

The functional characterisation of the commonest pathogenic allele at the receptor, showing what the mutant beta subunit does to TSHR signalling rather than inferring it from the frameshift.

PMID:39875149

Central congenital hypothyroidism due to TSHB gene mutation: 25-year follow-up.

1 finding

Long-term outcome in a single patient treated from the neonatal period: severe congenital hypothyroidism with neurocognitive sequelae averted by timely levothyroxine, and normal remaining anterior pituitary function.

PMID:26416826

Recent advances in central congenital hypothyroidism.

1 finding

Review establishing that T4-based newborn screening detects central congenital hypothyroidism where TSH-based screening cannot, and that the absence of a usable TSH signal makes treatment monitoring difficult.

PMID:25248602

Uncertainties in endocrine substitution therapy for central endocrine insufficiencies: hypothyroidism.

1 finding

States the scale of the entity - central hypothyroidism is about 1000-fold rarer than primary hypothyroidism - and the monitoring principle that levothyroxine dose in central hypothyroidism cannot be titrated on TSH.

PMID:34981755

TSHB R75G is a founder variant and prevalent cause of low or undetectable TSH in Indian Jews.

1 finding

Cited for a negative claim. The TSHB p.R75G founder variant, at ~4% carrier frequency in Bene Israel Indian Jews, does not impair TSH function; it defeats detection on some immunoassays and so mimics a low TSH in euthyroid people. It is the principal differential for an unexpectedly low TSH and is not a cause of this disease.

Deep Research

1

Deep research results are used as seeds for research; they do not undergo the same validation as the main records and may contain errors. How we use deep research.

Evaluations and curation notes (3)

Record notes

Entry scope, and the one decision a reader should check first, because the neighbouring entry already exists. `kb/disorders/Central_Congenital_Hypothyroidism.yaml` curates MONDO:0016410, the wider clinical category, and MONDO makes MONDO:0010139 a child of it. That entry already carries a `genetic:` row named "TSHB pathogenic variants", so the honest question is whether this should have been a `has_subtypes` row there instead of a separate entry. It is curated separately, on a mechanistic ground rather than an administrative one. The parent entry's pathograph is rooted at a node called "Impaired Hypothalamic-Pituitary TSH Drive", and that node is the wrong description of this disease. In TSHB deficiency the drive is not impaired: the hypothalamus and the thyrotroph work normally, and the hormone they produce cannot assemble into a functional heterodimer. The founding report showed exactly this - the mutant beta polypeptide is conformationally altered and cannot associate with the alpha subunit. Folding TSHB into a regulatory-drive node would assert a mechanism that is wrong for it, and the same applies in reverse to IGSF1, TBL1X, TRHR and IRS4, each of which does act upstream and each of which has its own MONDO term and its own extrathyroidal features (macroorchidism for IGSF1, sensorineural hearing loss for TBL1X). What the parent entry carries for TSHB today is a gene row with one citation and an inheritance block - not a pathograph. The two entries are therefore complementary rather than duplicative, and the relationship is now recorded explicitly in `mappings.mondo_mappings` as a `skos:broadMatch` to MONDO:0016410. The reciprocal gap - the parent entry carries no `mappings.mondo_mappings` block at all and does not cite MONDO:0010139 - is real and is left for a separate change rather than bundled into a curation PR for a different disease; it is recorded in `discussions`. This scoping was challenged rather than assumed. The automated second-opinion comment on the claim issue (dismech#12392) raised the parent entry and argued the subtype case; this note is the answer to it. Worth recording that the duplicate preflight for this claim searched `origin/main` for MONDO:0010139 and for the label "isolated thyroid-stimulating hormone deficiency" and found nothing - it did not search for `TSHB` or for "central congenital hypothyroidism", which is how an entry covering the same gene was missed. That is the exact failure the `claim-disease` skill warns about when it says the claim check cannot see a disease curated under a different term. This scoping is not hypothetical bookkeeping. The deep-research report used for this entry covers all five genes, and `just preflight-dr` returned WARN on exactly this basis, reporting IGSF1 mentioned 33 times against TSHB's 67 and warning that the report may mix in a second disease entity. Those sections were excluded rather than curated down. Nothing in this entry is sourced from the report's IGSF1, TBL1X, TRHR or IRS4 material. No `has_subtypes` rows are declared. The reported TSHB allele classes - a recurrent frameshift, missense alleles, a start-loss variant and a 5.4-kb deletion - all converge on absent or non-functional TSH, so there is no basis for splitting. Module conformance checked and left unset. `just list-modules` was read and `kb/modules/` grepped for `hypothalamic`, `pituitary`, `hormone`, `endocrine`, `thyroid` and `receptor signaling`. Nothing covers loss of a pituitary trophic hormone, so `conforms_to` is left off rather than forced onto a general signalling module. No GeneReviews chapter exists for this disorder. Checked offline with `just check-genereviews kb/disorders/Isolated_Thyroid-stimulating_Hormone_Deficiency.yaml` against the committed Bookshelf index; NO_CHAPTER for GeneReviews. Deep-research provenance and what was and was not taken from it. `research/Isolated_Thyroid-stimulating_Hormone_Deficiency-deep-research-openscientist.md` (provider openscientist, 26 citations). Two things from its own validation output were followed up rather than taken at face value: First, its reference validation listed `PMID:25248602` as unresolved with 8 mentions, which under the reference SOP would bar citing it. Re-fetched with `just fetch-reference PMID:25248602` on 2026-09-21: it resolves cleanly to Persani & Bonomi, "Uncertainties in endocrine substitution therapy for central endocrine insufficiencies: hypothyroidism", and contains both sentences the report quoted from it. The report's flag was a transport-level lookup failure, not a confabulation - which is the ambiguity the validator's own wording warns about. It is cited here, and this note records the re-check. Second, its term validation reported 8 of 14 checked labels as naming a different term. One of those is a substantive error rather than a formatting one: the report gives `CL:0000209` for "thyrotrope/thyrotropic cell of pars distalis". `CL:0000209` is *taste receptor cell*. The correct term, used in this entry, is `CL:0000476` thyrotroph, looked up in `cache/cl/terms.csv`. No CURIE in this entry was taken from the report without an independent lookup. The report's most valuable single contribution was a negative one and is curated in `discussions`: TSHB p.R75G, a founder variant reaching about 4% carrier frequency in Bene Israel Indian Jews, does *not* cause this disease. It leaves TSH function intact and merely defeats its detection on some immunoassay platforms. It was verified directly against PMID:34981755 before being recorded.

Review round 1 on PR #12400 · 2026-09-21T07:28:38Z · View source

Addressed all three IMPORTANT findings and both applicable suggestions from the ai4c-reviewer round on 261d12be. Finding 1, disconnected second root. Invisibility to TSH-Based Newborn Screening had no incoming edge. It is now downstream of Failure to Assemble Bioactive TSH Heterodimer, which is the right parent rather than the low-hormone state: the absent bioactive heterodimer is itself the analyte a TSH-based screen measures, so a screen looking for raised TSH reads normal in exactly the patients who have none. The pathograph now has a single root, Biallelic TSHB Loss of Function. Finding 2, four disconnected phenotypes. Hypotonia, Failure to thrive, Short stature and Intellectual disability are now downstream of Systemic Thyroid Hormone Deficiency, each on evidence the entry already carried on the phenotype itself. Finding 3, a prevalence note that contradicted its own numbers. The note claimed the pooled 3.3-7.7 per 100,000 range sat below the Dutch T4-screening figure of 1 in 16,000, and drew an ascertainment inference from that. 1 in 16,000 is 6.25 per 100,000, which is inside the range. The comparison was wrong and so was everything built on it. Rewritten to state that the two sources are consistent and that no ascertainment inference can be drawn, with the earlier mistake recorded rather than silently removed. Suggestion taken: the CAGYC conservation snippet is regraded from HUMAN_CLINICAL to OTHER. The quoted sentence is a comparative-sequence observation across paralogues, not a clinical finding in the patients, even though the variant was found by sequencing them. The reasoning is written into the explanation so the grade is not re-litigated. Suggestion taken in part: four further phenotypes named in a snippet the entry already holds are now curated with HPO bindings looked up rather than recalled - Hypothermia HP:0002045, Lethargy HP:0001254, Constipation HP:0002019, Umbilical hernia HP:0001537 - each wired from the systemic node on the same verified sentence. Generalized edema HP:0007430 was NOT added. The term resolves, but it comes from the deep-research report and no cached reference for this entry mentions edema, so there is no sentence to quote. Curating it would have meant inventing a snippet. Phenotype causal in-link coverage is now 11/11, 100 percent, from 3/7. Validation: just validate passes, 66/66 snippets verified, up from 53. check-duplicate-keys, check-entity-refs, check-causal-targets, check-qualifier-terms and check-snippet-grading all clean. The pathograph root check confirms a single root.

Create: Isolated Thyroid-stimulating Hormone Deficiency (TSHB) · 2026-09-21T04:53:56Z · View source

New DISEASE entry for MONDO:0010139, the TSHB-caused form of congenital central hypothyroidism. Scope decision. Curated as the TSHB entity only, not the wider clinical category of congenital central hypothyroidism. IGSF1, TBL1X, TRHR and IRS4 also cause central hypothyroidism and are each a different disease with its own MONDO term and its own extrathyroidal features. A kb/groupings/ record over the clinical differential is recorded as a CURATION_TODO discussion rather than created here. Deep research: research/Isolated_Thyroid-stimulating_Hormone_Deficiency-deep-research-openscientist.md, provider openscientist, 26 citations, run 2026-09-21. just preflight-dr against MONDO:0010139 returned WARN, reporting IGSF1 mentioned 33 times against TSHB's 67 and warning the report may mix in a second disease entity. That is exactly what it does; the IGSF1, TBL1X, TRHR and IRS4 sections were excluded rather than curated down, and nothing in this entry is sourced from them. Two items from the report's own validation output were followed up rather than accepted: - Its reference validation listed PMID:25248602 as unresolved (8 mentions), which would bar citing it. Re-fetched with just fetch-reference PMID:25248602 on 2026-09-21; it resolves cleanly to Persani & Bonomi, 'Uncertainties in endocrine substitution therapy for central endocrine insufficiencies: hypothyroidism', and contains both sentences the report quoted. The flag was a transport-level lookup failure, not a confabulation. It is cited in this entry and the re-check is recorded in the entry's notes as well as here. - Its term validation reported 8 of 14 checked labels as naming a different term. One is substantive: the report gives CL:0000209 for 'thyrotrope/thyrotropic cell of pars distalis'. CL:0000209 is taste receptor cell. This entry uses CL:0000476 thyrotroph, looked up in cache/cl/terms.csv. No CURIE in this entry was taken from the report without an independent lookup. The report's most valuable contribution was a negative one, verified directly against PMID:34981755 before recording: TSHB p.R75G, a founder variant at ~4% carrier frequency in Bene Israel Indian Jews, does not cause this disease. It leaves TSH function intact and defeats its detection on some immunoassay platforms, producing a spurious low TSH in euthyroid people. Without the report this entry would probably have curated it as a pathogenic founder allele, since it reads that way from a title search. It is curated as an INTERPRETATION discussion with a REFUTE evidence item. Curation notes. Invisibility to TSH-based newborn screening is modelled as a pathophysiology node rather than left in prose, because in this disorder the detection pathway determines the outcome as directly as the biology: everything downstream of it is preventable, and the within-kindred contrast in PMID:27362444 (three late-diagnosed relatives with neurodevelopmental retardation, the younger sibling treated from birth developing normally) is curated as a paired SUPPORT/REFUTE on the developmental-delay phenotype. The recurrent frameshift allele appears in the literature under two cDNA numberings (c.373delT and c.313delT) depending on whether the signal peptide is counted; the entry names it at protein level to avoid implying two alleles. No numeric reference intervals are recorded for TSH or free T4: the cited sources state directions but no intervals, and importing a conventional adult band into a congenital disorder would misstate the age-specific ranges. Validation. just validate passes with 50/50 snippets verified against cached references. just validate-terms, just check-entity-refs, just check-causal-targets and just check-duplicate-keys all pass. just check-genereviews reports NO_CHAPTER for both GeneReviews and StatPearls against the committed Bookshelf index snapshot of 2026-09-10, which is the basis for the no-chapter statement in the entry's notes. Four NCIT and CL identifiers were written from memory during drafting and were wrong: NCIT:C16340 (Biomedical Ethics, written as Blood Group Determination, in a sibling entry), NCIT:C38086 (Renography, written as Laboratory Procedure), NCIT:C177209 (Believe, written as Newborn Screening), and the report's CL:0000209. All were caught by just validate-terms or by cache lookup and replaced with looked-up terms. Recorded because the failure mode is the one CLAUDE.md describes under 'Every CURIE is read from a source in the same step it is written' and it recurred several times in one session.

OpenScientist ▸

Isolated Thyroid-stimulating Hormone Deficiency (i-TSHD) — Comprehensive Disease Characteristics Report

openscientist-autonomous 26 citations 2026-09-21T04:42:25.739367

Isolated Thyroid-stimulating Hormone Deficiency (i-TSHD) — Comprehensive Disease Characteristics Report

Target disease: Isolated Thyroid-stimulating Hormone Deficiency MONDO ID: MONDO:0010139 · Category: Mendelian OMIM: 275100 (TSH deficiency, isolated) · Orphanet: ORPHA:90673 (Central congenital hypothyroidism) · ICD-10: E03.1 (Congenital hypothyroidism without goiter) / E23.0 (Hypopituitarism) · MeSH: Hypothyroidism, Congenital

Summary

Isolated Thyroid-stimulating Hormone Deficiency (i-TSHD) is a rare Mendelian congenital central hypothyroidism in which the hypothalamic–pituitary unit fails to deliver sufficient bioactive thyroid-stimulating hormone (TSH/thyrotropin) to an intrinsically normal thyroid gland. The consequence is thyroid hormone deficiency (low free T4 and free T3) accompanied — paradoxically — by a TSH level that is low, normal, or undetectable rather than elevated. This biochemical signature is the defining feature of the disorder and its central clinical danger: TSH-based newborn screening programs miss these patients entirely, because they screen for the high TSH that characterizes far more common primary (thyroid-gland) hypothyroidism.

The disorder is genetically heterogeneous. The paradigmatic and most severe cause is biallelic (autosomal recessive) loss-of-function of TSHB, the gene encoding the beta subunit of TSH — this is the direct lesion that abolishes bioactive hormone. Four additional genes cause isolated central hypothyroidism through regulatory (upstream) mechanisms: IGSF1 (X-linked, the most prevalent single genetic cause), TBL1X, TRHR, and IRS4. Central hypothyroidism as a whole is roughly 1,000-fold rarer than primary hypothyroidism; the TSHB-based isolated form specifically is ultra-rare, with only dozens of families reported worldwide. Untreated, i-TSHD causes profound congenital hypothyroidism — historically termed cretinism — with severe mental and growth retardation. Yet it is one of the most gratifying diseases in endocrinology: early levothyroxine replacement fully prevents the neurodevelopmental catastrophe, and long-term follow-up confirms normal cognition when treatment begins in the neonatal period.

The therapeutic and monitoring paradigm has a critical twist. Because pituitary TSH is intrinsically deficient, it cannot be used to titrate replacement (unlike in primary hypothyroidism). Dosing must instead be guided by free T4 targeted to the mid-to-upper reference range plus clinical parameters. Prevention is necessarily secondary/tertiary: T4-based (or T4+TSH) newborn screening as practiced in the Netherlands, cascade family genetic testing once a familial variant is known, and genetic counseling (25% recurrence risk for recessive TSHB; consanguinity elevates risk). A key differential — and a subtle trap — is the TSHB p.R75G assay-interference variant, which produces spuriously "low" TSH on some immunoassays in clinically euthyroid people, mimicking hyperthyroidism rather than causing true deficiency.

Key Findings

1. Genetic architecture: five genes, one direct cause

Congenital isolated central hypothyroidism (i-TSHD / C-CH) is genetically heterogeneous but caused by a small, defined set of genes. Five genes are established: IGSF1, IRS4, TBL1X, TRHR, and TSHB (Sugisawa 2019, PMID: 31504637; Boelen 2021, PMID: 34225927). Among these, biallelic TSHB loss-of-function is the direct and most severe cause — it removes the hormone itself and is inherited in an autosomal recessive pattern. TSHB maps to chromosome 1p13 (HGNC:12372; NCBI Gene 7252).

In a Japanese cohort of 13 i-TSHD patients, genetic screening identified a causative mutation in 6/13 (46%) — five hemizygous IGSF1 mutations and one hemizygous TBL1X mutation — establishing IGSF1 as the most prevalent genetic cause of the isolated syndrome even though TSHB is the most severe. As the authors state: "Five genes (IGSF1, IRS4, TBL1X, TRHR, and TSHB) responsible for the disease have been identified" and "Genetic screening of the 13 study subjects revealed six mutation-carrying patients (46%), including five hemizygous IGSF1 mutation carriers and one hemizygous TBL1X mutation carrier" (PMID: 31504637). More than half of clinically diagnosed cases remain genetically unexplained, indicating additional causal loci await discovery.

2. TSHB c.373delT: a recurrent, worldwide founder-like mutation

The single most important TSHB allele is the frameshift c.373delT in exon 3 (p.Cys105Valfs*114). It has been reported in patients from Brazil, Germany, Belgium, USA, Switzerland, Argentina, France, Portugal, the UK and Ireland (Borges 2019, PMID: 31166470): "The c.373delT mutation has previously been reported in patients from Brazil, Germany, Belgium." In the UK/Ireland series, affected individuals were homozygous or compound heterozygous for c.373delT combined with a 5.4-kb TSHB deletion or a novel p.Met1? start-loss variant (Nicholas 2017, PMID: 27362444): "the affected individuals were compound heterozygous for TSHB c.373delT and either a 5·4-kB TSHB deletion." This demonstrates that both point mutations and large structural deletions contribute to the TSHB mutational spectrum. Functionally, in vitro work shows the C105Vfs114X variant yields a modified/abrogated signaling profile at the TSH receptor (TSHR) (Kalveram 2019, PMID: 31703413).

Other reported pathogenic TSHB variants include the exon-2 missense alleles first described in consanguineous Japanese families (Tatsumi & Miyai 1991, PMID: 1762181), p.E32K (c.94G>A) in two homozygous siblings (PMID: 28515030), and p.Cys105Arg (c.313T>C) in a consanguineous infant (PMID: 42256321).

3. Invisible to TSH screening; curable with early levothyroxine

The biochemical hallmark is low free T4 and free T3 with inappropriately low/normal/undetectable TSH (Draidi 2026, PMID: 42256321; Asirvatham 2025, PMID: 39875149). Because TSH is not elevated, TSH-based congenital-hypothyroidism screening cannot detect these cases — the central diagnostic pitfall: "Isolated TSH deficiency is not detected by routine TSH-based neonatal screening, representing a clinical challenge" (PMID: 31166470). T4-based programs, such as the Netherlands' heel-prick T4 screen, detect both primary and central CH (PMID: 34225927).

The clinical stakes of missing the diagnosis are severe but the treatment is curative. In one UK/Ireland kindred, "the younger sibling in kindred 1 developed normally following genetic diagnosis and treatment from birth" — while late-treated relatives had intellectual disability (PMID: 27362444). A 25-year follow-up concluded: "Despite having severe congenital hypothyroidism, timely initiation of levothyroxine averted neurocognitive sequelae" (PMID: 39875149). Early, adequate replacement therefore converts a devastating disorder into one with normal outcomes.

4. Two mechanistic classes: direct (TSHB) vs. regulatory (IGSF1/TBL1X/TRHR/IRS4)

The five genes fall into two mechanistically distinct groups:

TSHB (direct): mutations abolish or modify bioactive TSH presented to TSHR (PMID: 31703413). The lesion is at the hormone itself; the phenotype is the purest, most severe isolated deficiency.
IGSF1 (X-linked, Xq26; regulatory): a hypothalamic/pituitary membrane glycoprotein. IGSF1 deficiency reduces TSH production, decreases TRHR expression, and lowers TSH biopotency. "IGSF1 stimulates transcription of the thyrotropin-releasing hormone receptor (TRHR) by negative modulation of the TGFβ1-Smad signaling pathway, and enhances the synthesis and biopotency of TSH" (García 2017, PMID: 28262687). Clinically it is a syndrome: macroorchidism, variable prolactin deficiency, transient partial GH deficiency, increased waist circumference, and mild attentional deficits (Joustra 2016, PMID: 26840047; Brûlé 2022, PMID: 35708735).
TBL1X (regulatory): a subunit of the NCoR/SMRT thyroid-hormone-receptor corepressor complex; mutations cause mild central hypothyroidism plus sensorineural hearing loss. "TBL1X mutations are associated with CeH and hearing loss" (Heinen 2016, PMID: 27603907; Hu 2024, PMID: 39316725).
TRHR (regulatory): loss-of-function (e.g., p.I131T) reduces TRH affinity and Gq signaling. "The I131T mutation, in TRHR intracellular loop 2, decreases TRH affinity and increases the half-maximal effective concentration for signaling" (García 2017, PMID: 28419241).
IRS4 (regulatory): part of the hypothalamic insulin/leptin signaling cascade; mutations cause familial isolated central hypothyroidism (Heinen 2018, PMID: 30061370).

5. TSHB p.R75G: an assay-interference variant, NOT a loss-of-function allele

A crucial diagnostic caveat: homozygosity for TSHB p.R75G does not alter TSH bioactivity but abrogates its detection by some immunoassay platforms, producing spurious "low/undetectable TSH" and erroneous diagnoses of hyperthyroidism in clinically euthyroid individuals (Shaki 2022, PMID: 34981755): "Homozygosity for the TSHB p.R75G variant... does not alter TSH function but abrogates its detection by some immune detection-based platforms, leading to erroneous diagnosis of hyperthyroidism." The variant is a founder allele with an "Extremely high carrier rate of p.R75G TSHB in Bene Israel Indian Jews (~4%)", sharing a 239.7-kb haplotype block with South Asian populations. This is the mirror image of true i-TSHD — same gene, opposite clinical meaning — and must be excluded when interpreting an unexpectedly low TSH.

6. Epidemiology: ~1,000-fold rarer than primary hypothyroidism

Central hypothyroidism (CeH) is "about 1000-fold rarer than PH [primary hypothyroidism]" (Persani & Bonomi 2014, PMID: 25248602). Independent estimates place CeH at "approximately 1:50,000" (Benvenga 2018, PMID: 30294553), while central congenital hypothyroidism as a whole "may be more prevalent than previously thought, affecting up to 1:16,000 neonates in the Netherlands" under T4-based screening (Schoenmakers 2015, PMID: 26416826). The isolated TSHB-based subset is a small fraction of this — only dozens of families reported worldwide, with roughly 74 single-gene i-TSHD patients reviewed by Sugisawa 2019 (PMID: 31504637).

7. Severity: cretinism when untreated; recessive consanguineous origin

Congenital isolated TSH deficiency "is rare disease causing hypothyroidism including cretinism, severe mental and growth retardation" (Tatsumi & Miyai 1991, PMID: 1762181). The disorder was first defined in three consanguineous Japanese families sharing an exon-2 TSHB missense mutation. Modern neonatal presentations include prolonged unconjugated (neonatal) hyperbilirubinemia/jaundice, failure to thrive, generalized edema, hypotonia, and global developmental delay when diagnosis is delayed (Asirvatham 2025, PMID: 39875149: "a female term neonate presenting with prolonged unconjugated hyperbilirubinaemia"; Draidi 2026, PMID: 42256321). In the isolated form, other anterior pituitary hormones and pituitary MRI are normal (PMID: 39875149).

8. Treatment: lifelong levothyroxine, monitored by free T4 (not TSH)

Treatment is lifelong levothyroxine (L-T4) replacement. The distinctive challenge is monitoring: because TSH is already low/inappropriate, it cannot be used to titrate dose. "L-T4 replacement in CeH should rely on the combined evaluation of several biochemical and clinical parameters in order to overcome the lack of accuracy of the single index" (Persani & Bonomi 2014, PMID: 25248602) — with free T4 targeted to the mid-to-upper reference range as the chief guide. Schoenmakers 2015 emphasizes the monitoring gap: "Since TSH cannot be used as an indicator of euthyroidism, adequacy of treatment can be difficult to monitor due to a paucity of alternative biomarkers" (PMID: 26416826). Early adequate L-T4 from birth yields normal neurodevelopment (PMID: 27362444; PMID: 39875149). NCIT term: Levothyroxine (NCIT:C29216).

9. Prevention: T4 screening, cascade testing, genetic counseling

Because the disorder is congenital and monogenic, prevention is secondary/tertiary rather than primary. Three pillars: (1) T4- or T4+TSH-based newborn screening (not TSH-only) for early detection (PMID: 26416826; PMID: 34225927); (2) cascade family testing once a familial TSHB variant is known — "Identification of affected and carriers allows the diagnosis, treatment and adequate genetic counseling" (PMID: 31166470); and (3) genetic counseling, noting the 25% per-pregnancy recurrence risk for autosomal-recessive TSHB and elevated risk with consanguinity (PMID: 1762181). The differential diagnosis must exclude the p.R75G assay-interference variant (PMID: 34981755).

10. Model organisms and comparative biology

No animal model isolates TSHB deficiency cleanly, but dwarf mouse mutants validate the TSH-biosynthesis axis. Snell (dw) and Jackson dwarf mice carry Pit1/Pou1f1 mutations causing combined loss of GH, prolactin, and TSH: "Two nonallelic mouse mutations with severe dwarf phenotypes are characterized by a lack of growth hormone, prolactin, and thyroid stimulating hormone" (Camper 1990, PMID: 1981057). "Mutations of the pituitary transcription factor gene POU1F1... are responsible for deficiencies of GH, prolactin and thyroid stimulating hormone (TSH) in Snell and Jackson dwarf mice and in man" (Wu 1998, PMID: 9462743). The Ames dwarf (df) mouse carries a Prop1 mutation upstream of Pit1. These are combined pituitary hormone deficiency models (not isolated TSH deficiency) but demonstrate the thyrotrope-differentiation branch (POU1F1 → TSHB transcription → TSH). The hyt/hyt mouse (Tshr loss-of-function) models TSH resistance downstream. Human/mouse orthology: mouse Tshb (NCBI Gene 22094) ↔ human TSHB (NCBI Gene 7252). Naturally, central hypothyroidism occurs in Miniature Schnauzer dogs, some with disproportionate dwarfism and combined TSH/prolactin deficiency, though "No disease-causing mutations were found in the TSHB gene and the exons of the TRHR gene of these Schnauzers" — the canine genetic basis remains unresolved (Voorbij 2016, PMID: 26696394).

Detailed Section-by-Section Report

1. Disease Information

i-TSHD is a congenital central (secondary/tertiary) hypothyroidism in which the thyroid gland is intrinsically normal but receives inadequate bioactive TSH stimulation. Identifiers: MONDO:0010139; OMIM 275100 (TSH deficiency, isolated); Orphanet ORPHA:90673 (central congenital hypothyroidism); ICD-10 E03.1/E23.0; ICD-11 5A00.1 (central hypothyroidism); MeSH "Congenital Hypothyroidism." Synonyms/alternatives: isolated TSH deficiency; congenital central hypothyroidism (C-CH/CCH); isolated central hypothyroidism (CeH); thyrotropin deficiency; secondary hypothyroidism (when pituitary), tertiary (when hypothalamic). Information is derived largely from aggregated disease-level resources (OMIM, Orphanet) supplemented by individual patient case reports and small kindred series — this is a rare disease characterized case-by-case.

2. Etiology

Causal factors are genetic (monogenic Mendelian). Primary cause: biallelic TSHB loss-of-function (autosomal recessive). Additional causal genes: IGSF1 (X-linked, most prevalent), TBL1X, TRHR, IRS4 (Findings 1, 4). Genetic risk factors: consanguinity is a major risk factor for recessive TSHB disease (PMID: 1762181); founder alleles (c.373delT worldwide; p.R75G in specific populations, though the latter is assay interference). Environmental risk factors: none established as causal for the Mendelian form. Protective factors: not applicable/not established (this is a monogenic disorder). Gene–environment interactions: the principal clinically relevant "interaction" is between the p.R75G genotype and the immunoassay platform used — an analytical, not biological, interaction that determines whether TSH appears falsely low (PMID: 34981755).

3. Phenotypes

Phenotype	Type	HPO term	Onset	Severity/Frequency
Central/secondary hypothyroidism (low FT4/FT3, low-normal TSH)	Lab abnormality	HP:0011787 (Central hypothyroidism)	Congenital/neonatal	Defining; severe if untreated
Congenital hypothyroidism	Lab/clinical	HP:0000851	Congenital	Severe
Prolonged neonatal jaundice (unconjugated)	Clinical sign	HP:0006579	Neonatal	Common presenting sign
Failure to thrive	Clinical sign	HP:0001508	Neonatal/infancy	Common if delayed dx
Generalized edema / myxedema	Physical	HP:0007430	Neonatal	In untreated cases
Hypotonia	Clinical sign	HP:0001252	Neonatal/infancy	Common if delayed dx
Global developmental delay / intellectual disability ("cretinism")	Clinical	HP:0001263 / HP:0001249	Infancy	Severe if untreated; preventable
Growth retardation / short stature	Clinical	HP:0004322	Childhood	If untreated
Sensorineural hearing loss (TBL1X only)	Clinical	HP:0000407	Congenital	TBL1X subtype
Macroorchidism (IGSF1 only)	Physical	HP:0000053	Puberty/adult	IGSF1 syndrome

Quality of life: With early treatment, QoL and cognition are essentially normal; IGSF1 patients may show mild attentional deficits and increased mental fatigue even when treated (PMID: 26387489). Untreated disease produces lifelong severe disability.

4. Genetic/Molecular Information

Causal genes: TSHB (1p13, HGNC:12372, OMIM 188540), IGSF1 (Xq26, X-linked), TBL1X (Xp22.31), TRHR (8q23), IRS4 (Xq22). Variant types in TSHB: frameshift (c.373delT/p.C105Vfs*114), missense (p.E32K, p.C105R, exon-2 missense), start-loss (p.Met1?), and structural (5.4-kb deletion) (Finding 2; PMID: 27362444). Classification: pathogenic/likely pathogenic per ACMG for the recurrent alleles. Functional consequence: loss of function (absent/abrogated bioactive TSH); p.R75G is a special case of assay non-detection without functional loss (Finding 5). Origin: germline. Allele frequency: ultra-rare in gnomAD for pathogenic alleles; p.R75G reaches ~4% carrier frequency in Bene Israel Indian Jews (founder effect). Modifier genes / epigenetics / chromosomal abnormalities: none established for the isolated form.

5. Environmental Information

Not applicable as a primary cause — i-TSHD is monogenic. No toxins, infectious agents, or lifestyle factors are established causes. (Broader central hypothyroidism can be acquired via pituitary tumor, trauma, or infiltrative disease, but these fall outside the Mendelian i-TSHD entity and belong in the differential diagnosis.)

6. Mechanism / Pathophysiology — causal chain

Direct (TSHB) branch: 1. Biallelic loss-of-function TSHB mutation → leads to absent or bioinactive TSH beta subunit. 2. → results in failure to assemble functional heterodimeric TSH (α+β). 3. → results in no/insufficient bioactive TSH signaling at the thyroid TSHR (Gs/cAMP pathway). 4. → leads to failure of thyroid follicular cells to synthesize/secrete T4 and T3. 5. → results in low circulating free T4 and free T3 (with low/normal/undetectable, TRH-unresponsive TSH). 6. → leads to systemic thyroid hormone deficiency affecting CNS myelination/maturation, growth, and metabolism. 7. → results in congenital hypothyroidism (jaundice, edema, hypotonia, failure to thrive) and — if untreated — irreversible neurodevelopmental/growth retardation (cretinism).

Regulatory (upstream) branches feed into steps 2–4 from above the pituitary hormone itself: - TRHR loss → reduced TRH signaling (Gq) in thyrotropes → decreased TSH synthesis/release (inferred to reduce both amount and biopotency). - IGSF1 loss → reduced TRHR transcription (via TGFβ1-Smad modulation) + reduced TSH synthesis/biopotency + reduced Tshb expression (demonstrated in Igsf1-knockout mice, PMID: 35708735). - TBL1X loss → disturbed NCoR/SMRT corepressor complex → altered thyroid-hormone-receptor–mediated transcription (context-dependent; PMID: 39316725) → mild CeH + hearing loss. - IRS4 loss → impaired hypothalamic insulin/leptin signaling → reduced central drive to the HPT axis.

Molecular pathways / GO terms: GO:0002154 (thyroid hormone mediated signaling pathway), GO:0007186 (G-protein-coupled receptor signaling), GO:0038194 (thyroid-stimulating hormone signaling), GO:0007165 (signal transduction). Cell types (CL): thyrotrope/thyrotropic cell of pars distalis (CL:0000209), thyroid follicular cell (CL:0002258). Upstream vs downstream: TRHR/IGSF1/IRS4 (hypothalamic-pituitary regulatory) are upstream; TSHB (hormone) is central; thyroid follicular response and peripheral tissue effects are downstream.

7. Anatomical Structures Affected

Primary organ: anterior pituitary gland (adenohypophysis, UBERON:0002196) — specifically thyrotropes; and/or hypothalamus (UBERON:0001898) for TRHR/IGSF1/IRS4.
Secondary: thyroid gland (UBERON:0002046) — structurally normal but understimulated; downstream effects on brain (UBERON:0000955), skeleton, liver (neonatal jaundice), heart (reversible cardiomyopathy reported in a syndromic case, PMID: 42256321).
Body system: endocrine system (hypothalamic–pituitary–thyroid axis).
Subcellular (GO CC): secretory granules/secretory pathway (GO:0030141), endoplasmic reticulum (GO:0005783) for hormone folding/assembly, plasma membrane (IGSF1, TRHR).
Localization/lateralization: bilateral/systemic (endocrine), not lateralized. TBL1X-associated hearing loss is typically bilateral.

8. Temporal Development

Onset: congenital; biochemical deficiency present from birth. Clinical signs (jaundice, hypotonia, poor feeding) appear in the neonatal period; developmental delay emerges over infancy if untreated.
Onset pattern: chronic/insidious; the danger is that neonates may appear near-normal at birth, and some IGSF1 cases develop CeH over time (PMID: 35350016).
Progression: without treatment, progressive and irreversible neurodevelopmental damage; with treatment, stable and normal.
Disease course: lifelong (chronic) requiring lifelong L-T4.
Critical period: the neonatal/early-infancy window is decisive for neurodevelopmental outcome — the key opportunity for intervention.

9. Inheritance and Population

Epidemiology: CeH ~1:50,000; CCH up to 1:16,000 neonates (Netherlands, T4 screening); isolated TSHB form ultra-rare (dozens of families; ~74 single-gene i-TSHD patients reviewed) (Finding 6).
Inheritance: TSHB — autosomal recessive; IGSF1, TBL1X, IRS4 — X-linked; TRHR — autosomal recessive.
Penetrance/expressivity: TSHB biallelic LoF — high penetrance, severe; IGSF1 — variable expressivity, even within families carrying identical deletions (PMID: 27146357); female carriers of X-linked variants may show mild/subclinical FT4 reduction.
Consanguinity: a major factor for recessive TSHB (PMID: 1762181).
Founder effects: c.373delT (widespread pathogenic); p.R75G (~4% carriers in Bene Israel Indian Jews — assay-interference allele).
Recurrence risk: 25% per pregnancy for recessive TSHB carrier couples.
Sex ratio: X-linked subtypes (IGSF1, TBL1X, IRS4) predominantly affect males; TSHB and TRHR affect both sexes equally.

10. Diagnostics

Laboratory (definitive): low free T4 (LOINC 3024-7) and low free T3 with low/normal/undetectable TSH (LOINC 3016-3); blunted or absent TSH response to TRH stimulation; normal other anterior pituitary hormones in the isolated form.
Imaging: normal pituitary MRI in isolated forms (distinguishes from combined pituitary hormone deficiency/structural hypopituitarism).
Genetic testing: targeted single-gene TSHB sequencing (including deletion/CNV analysis to catch the 5.4-kb deletion), gene panels covering TSHB/IGSF1/TBL1X/TRHR/IRS4, or whole-exome sequencing for unexplained cases. WES/WGS increasingly first-line given heterogeneity.
Clinical criteria: central hypothyroidism = low FT4 with non-elevated TSH; genetic confirmation defines the Mendelian subtype.
Differential diagnosis: combined pituitary hormone deficiency/hypopituitarism (additional hormone deficits, abnormal MRI); acquired central hypothyroidism (tumor, trauma, infiltration); non-thyroidal illness (sick euthyroid); and critically the TSHB p.R75G assay-interference variant mimicking low TSH in euthyroid individuals (Finding 10 / 5).
Screening: T4-based newborn screening detects it; TSH-based screening misses it; cascade family testing for known variants.

11. Outcome/Prognosis

Survival/life expectancy: normal with treatment; the disorder is not directly life-limiting when managed.
Morbidity: if untreated — severe, permanent intellectual disability and growth failure (cretinism). If treated early — minimal; near-normal function (PMID: 39875149).
Complications: neonatal — reversible cardiomyopathy and hypoglycemia in severe/syndromic cases (PMID: 42256321); untreated — irreversible neurocognitive deficit.
Recovery potential: neurodevelopmental damage is preventable but not reversible once established — hence the premium on early diagnosis.
Prognostic factors: age at treatment initiation is the dominant prognostic factor; earlier = better. Free T4 adequacy during treatment predicts outcome.

12. Treatment

Pharmacotherapy: Levothyroxine (L-T4) — lifelong oral thyroid hormone replacement (NCIT:C29216; DrugBank DB00451; ATC H03AA01). Mechanism: exogenous T4 restores circulating thyroid hormone, bypassing the deficient TSH-thyroid stimulation.
Monitoring: free T4 targeted to mid-to-upper reference range plus clinical parameters — NOT TSH (Finding 8; PMID: 25248602).
Advanced/experimental therapeutics: none required or established; no gene/cell/RNA therapy — L-T4 is fully effective.
Pharmacogenomics: not established for this disorder beyond standard L-T4 considerations.
Treatment outcomes: excellent when started neonatally; normal neurodevelopment documented at 25-year follow-up.
Personalized medicine: genotype-guided recognition matters chiefly for (a) recognizing screening-negative TSHB cases early and (b) avoiding mistreatment of p.R75G "pseudo-hyperthyroidism."

13. Prevention

Primary prevention: not possible (congenital, monogenic).
Secondary prevention: T4-based newborn screening (detects central CH); genetic cascade/carrier screening in affected families; prenatal/preimplantation testing where a familial variant is known.
Tertiary prevention: early L-T4 to prevent neurodevelopmental complications; lifelong FT4-guided monitoring.
Counseling: genetic counseling for recurrence risk (25% recessive TSHB; X-linked risk assessment for IGSF1/TBL1X/IRS4); "Identification of affected and carriers allows the diagnosis, treatment and adequate genetic counseling" (PMID: 31166470).
Public health: advocacy for adding T4 (or T4+TSH) to newborn screening panels where only TSH is measured.

14. Other Species / Natural Disease

Natural disease: central hypothyroidism occurs naturally in Miniature Schnauzer dogs (Canis lupus familiaris, NCBI Taxon 9615), some with disproportionate dwarfism and combined TSH/prolactin deficiency; TSHB/TRHR coding mutations were excluded, so the canine basis is unresolved (PMID: 26696394).
Orthologous genes: mouse Tshb (NCBI Gene 22094), human TSHB (NCBI Gene 7252); canine ortholog exists.
Comparative biology: the mammalian HPT axis and TSHB are evolutionarily conserved; dwarf-mouse models demonstrate cross-species conservation of the POU1F1→TSHB→TSH pathway.
Zoonotic potential: none (non-communicable genetic disorder).

15. Model Organisms

Mouse (mammalian): Snell (dw) and Jackson dwarfs (Pit1/Pou1f1 mutations) and Ames (df) dwarf (Prop1) — combined GH/PRL/TSH deficiency; recapitulate the thyrotrope-differentiation and TSH-loss branch but not isolated TSHB deficiency (PMID: 1981057; PMID: 9462743).
Igsf1-knockout mouse: reduced pituitary Tshb and variably reduced Trhr; models the IGSF1 regulatory mechanism (PMID: 35708735).
hyt/hyt mouse: Tshr loss-of-function — models TSH resistance (downstream), not TSHB deficiency.
Model limitation: no model cleanly isolates TSHB deficiency; dwarf models carry combined deficiencies, limiting attribution to the TSH axis alone.
Resources: MGI, IMPC, IMSR for murine alleles.

Mechanistic Model / Interpretation

      UPSTREAM (regulatory genes)                       DIRECT (hormone gene)
   ┌───────────────────────────────────────────┐      ┌──────────────────────────────┐
   │ TRHR loss  → ↓TRH→Gq signaling in           │      │ TSHB biallelic LoF           │
   │ IGSF1 loss → ↓TRHR transcription (TGFβ-Smad) │      │  → absent/bioinactive        │
   │           → ↓TSH synthesis & biopotency      │      │    TSH β subunit             │
   │ IRS4 loss  → ↓hypothalamic insulin/leptin    │      └──────────────┬───────────────┘
   │ TBL1X loss → NCoR/SMRT corepressor defect    │                     │
   └───────────────────────┬─────────────────────┘                     │
           ▼                                            ▼
 ↓ Thyrotrope output of BIOACTIVE TSH  ◄─────────────────┘
           │
           ▼
↓ TSHR (Gs/cAMP) stimulation of thyroid follicular cells
           │
           ▼
      ↓ Synthesis/secretion of T4 & T3
           │
           ▼
   LOW free T4 / free T3  +  LOW/normal/UNDETECTABLE TSH (TRH-unresponsive)
           │
┌──────────────────┴───────────────────┐
▼                                       ▼
  INVISIBLE to TSH-based                 Systemic thyroid hormone deficiency
  newborn screening                      (CNS myelination, growth, metabolism)
│                                       │
▼                                       ▼
  Delayed diagnosis ───────────────►  Untreated: cretinism (irreversible)
│                             Early L-T4 (FT4-guided): NORMAL outcome
▼
  Prevention: T4-based screening + cascade genetic testing + counseling

Key interpretive points: (1) The disorder has a two-tier genetic architecture — a direct hormone defect (TSHB) and four regulatory defects (IGSF1/TBL1X/TRHR/IRS4) — that converge on a single final common pathway: insufficient bioactive TSH at the thyroid. (2) The low-TSH biochemistry is simultaneously the diagnostic signature and the reason the disease slips through TSH-only screening. (3) The p.R75G paradox shows that a TSHB variant can produce identical-looking biochemistry (low TSH) with the opposite clinical meaning (euthyroid), underscoring that assay behavior must be interpreted alongside genotype and free thyroid hormones. (4) Because the endpoint is a hormone that can be replaced pharmacologically, the disease is fully treatable — the entire prognosis hinges on timing of diagnosis, not on any limitation of therapy.

Evidence Base

PMID	Paper (abbrev.)	Supports finding(s)	Evidence type
31504637	Sugisawa 2019 — Genetics of congenital i-TSHD	1, 6 (five genes; IGSF1 predominance; ~74 patients)	Human cohort + review
31166470	Borges 2019 — Recurrent TSHB mutation undetectable in screening	2, 3, 9 (c.373delT worldwide; screening pitfall; cascade counseling)	Human clinical
27362444	Nicholas 2017 — TSHβ defects UK/Ireland	2, 3, 8 (compound het; 5.4-kb deletion; early tx normal)	Human clinical
31703413	Kalveram 2019 — C105Vfs114X at TSHR	2, 4 (modified TSHR signaling)	In vitro
34981755	Shaki 2022 — TSHB R75G founder variant	5, 9 (assay interference; ~4% carriers)	Human genetics
39875149	Asirvatham 2025 — TSHB CCH 25-yr follow-up	3, 7, 8 (jaundice; early tx averts sequelae)	Human clinical
42256321	Draidi 2026 — ADAR+TSHB infant	3, 7 (biochemistry; reversible cardiomyopathy)	Human case
25248602	Persani & Bonomi 2014 — CeH substitution therapy	6, 8 (1000-fold rarer; FT4-guided dosing)	Review
26416826	Schoenmakers 2015 — CCH review	6, 8 (1:16,000; monitoring gap)	Review
30294553	Benvenga 2018 — CeH congenital etiologies	6 (~1:50,000)	Review
28262687	García 2017 — IGSF1 controls TRHR	4 (IGSF1 regulatory mechanism)	Mechanistic
28419241	García 2017 — TRHR mutation	4 (TRHR ligand affinity/Gq)	Mechanistic
27603907	Heinen 2016 — TBL1X	4 (CeH + hearing loss)	Human genetics
30061370	Heinen 2018 — IRS4	4 (IRS4 familial CeH)	Human genetics
26840047	Joustra 2016 — IGSF1 case series	4 (IGSF1 syndrome; most common genetic cause)	Human cohort
35708735	Brûlé 2022 — Igsf1 KO mouse	4, 10 (reduced Tshb)	Mouse model
1762181	Tatsumi & Miyai 1991 — first TSHB cases	7, 9 (cretinism; recessive consanguineous)	Human genetics
1981057	Camper 1990 — Pit1/Snell dwarf	10 (dwarf models)	Mouse model
9462743	Wu 1998 — POU1F1/PROP1	10 (cross-species conservation)	Human/mouse
26696394	Voorbij 2016 — Schnauzer CeH	10 (natural canine disease)	Veterinary
39316725	Hu 2024 — TBL1X in liver cells	4 (TH-action mechanism)	In vitro

Limitations and Knowledge Gaps

Case-based evidence. Because the isolated TSHB form is ultra-rare (dozens of families worldwide), most clinical knowledge derives from case reports and small kindreds rather than powered cohorts. Frequency figures for individual phenotypes are qualitative.
>50% of cases unexplained. In Sugisawa's cohort only 46% carried an identifiable mutation; additional causal genes for isolated central hypothyroidism almost certainly remain undiscovered.
No clean animal model. All available mouse models (Snell, Jackson, Ames) carry combined pituitary hormone deficiencies; there is no widely used isolated Tshb-knockout that models the human disease purely. This limits mechanistic dissection of TSHB-specific effects.
Monitoring biomarker gap. Because TSH cannot indicate euthyroidism in CeH, and free T4 targets are imperfect, there is a genuine paucity of validated biomarkers to confirm adequate replacement — an open clinical problem.
Canine genetic basis unresolved. Natural central hypothyroidism in Miniature Schnauzers lacks an identified mutation, so comparative-biology insights are incomplete.
p.R75G under-recognition. The assay-interference variant is likely under-recognized outside the populations where it has been studied, risking misdiagnosis.
Epigenetics, modifiers, environment. No modifier genes, epigenetic mechanisms, or environmental contributors have been characterized for the isolated Mendelian form — this may reflect true absence or simply lack of study.

Proposed Follow-up Experiments / Actions

Advocate for T4-inclusive newborn screening. Quantify how many i-TSHD cases are missed under TSH-only programs versus T4-based programs; use this to support policy change in jurisdictions screening TSH alone.
Gene discovery in unexplained cases. Apply whole-genome sequencing and transcriptomic/functional follow-up to the >50% of genetically unexplained isolated central hypothyroidism cohorts to identify novel causal loci.
Generate an isolated Tshb-knockout mouse (or conditional thyrotrope-specific line) to model the pure disease, enabling clean study of TSHB-specific biology and testing of early-replacement timing windows.
Develop/validate alternative monitoring biomarkers for CeH replacement adequacy (e.g., tissue-based markers of thyroid hormone action such as SHBG, ferritin, or ankle-reflex/metabolic indices) to overcome the "TSH-can't-be-used" problem.
Population screening for TSHB p.R75G on relevant immunoassay platforms in founder populations to prevent misdiagnosis of hyperthyroidism; consider laboratory flagging of discordant low-TSH/normal-FT4 results.
Resolve the canine genetic basis in Miniature Schnauzers via whole-genome sequencing, potentially revealing a novel HPT-axis regulator relevant to unexplained human cases.
Establish a longitudinal i-TSHD registry integrating genotype, screening method, age at treatment, FT4 trajectories, and neurodevelopmental outcomes to define natural history and optimize FT4 targets.

Report compiled from 11 confirmed findings across 5 investigative iterations and 49 reviewed papers. Evidence types are labeled human clinical, human genetics, mechanistic/in vitro, mouse model, and veterinary throughout.

Artifacts

Reference Validation

Checked with linkml-reference-validator 0.2.1.

Outcome	Count
References checked	26
Resolved	25
Unresolved (possible confabulation)	1
Unverifiable	0
References weighed for topical relevance	25
On topic	20
Off topic	0

Unresolved references

These identifiers did not resolve to a record and may be fabricated. A lookup that failed for transport reasons is indistinguishable from one that failed because the record does not exist, so spot-check before acting on them:

PMID:25248602 (8 mentions) - Identifier did not resolve to a record

Term Validation

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

Outcome	Count
Terms checked	27
Resolved	25
Unresolved (possible confabulation)	0
Obsolete	0
Unverifiable	2
Terms whose name was checked	14
Terms named correctly	2
Terms named as a different term	8
Terms whose name is worth a second look	4

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:0000851 (1 mention) - the report calls it "Lab/clinical"; HP calls it Congenital hypothyroidism
HP:0006579 (1 mention) - the report calls it "Clinical sign"; HP calls it Prolonged neonatal jaundice
HP:0001508 (1 mention) - the report calls it "Clinical sign"; HP calls it Failure to thrive
HP:0007430 (1 mention) - the report calls it "Physical"; HP calls it Generalized edema
HP:0001252 (1 mention) - the report calls it "Clinical sign"; HP calls it Hypotonia
HP:0004322 (1 mention) - the report calls it "Clinical"; HP calls it Short stature
HP:0000407 (1 mention) - the report calls it "Clinical"; HP calls it Sensorineural hearing impairment
HP:0000053 (1 mention) - the report calls it "Physical"; HP calls it Macroorchidism

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:

GO:0002154 (1 mention) - the report calls it "thyroid hormone mediated signaling pathway"; GO calls it thyroid hormone receptor signaling pathway, and lists "thyroid hormone mediated signalling pathway" among its other names
GO:0007186 (1 mention) - the report calls it "G-protein-coupled receptor signaling"; GO calls it G protein-coupled receptor signaling pathway
GO:0038194 (1 mention) - the report calls it "thyroid-stimulating hormone signaling"; GO calls it thyroid-stimulating hormone signaling pathway
UBERON:0002046 (1 mention) - the report calls it "Secondary: thyroid gland"; UBERON calls it thyroid gland**

Terms named inconsistently

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

ORPHA:90673 - called "Central congenital hypothyroidism", "central congenital hypothyroidism"

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.

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Mappings

Inheritance

Discussions and Knowledge Gaps

Pathophysiology

Pathograph

Phenotypes

Genetic Associations

Medical Actions

Biochemical Markers

Diagnosis

Prevalence

Clinical Burden

Source YAML

References & Deep Research

References

Deep Research

Isolated Thyroid-stimulating Hormone Deficiency (i-TSHD) — Comprehensive Disease Characteristics Report

Summary

Key Findings

1. Genetic architecture: five genes, one direct cause

2. TSHB c.373delT: a recurrent, worldwide founder-like mutation

3. Invisible to TSH screening; curable with early levothyroxine

4. Two mechanistic classes: direct (TSHB) vs. regulatory (IGSF1/TBL1X/TRHR/IRS4)

5. TSHB p.R75G: an assay-interference variant, NOT a loss-of-function allele

6. Epidemiology: ~1,000-fold rarer than primary hypothyroidism

7. Severity: cretinism when untreated; recessive consanguineous origin

8. Treatment: lifelong levothyroxine, monitored by free T4 (not TSH)

9. Prevention: T4 screening, cascade testing, genetic counseling

10. Model organisms and comparative biology

Detailed Section-by-Section Report

1. Disease Information

2. Etiology

3. Phenotypes

4. Genetic/Molecular Information

5. Environmental Information

6. Mechanism / Pathophysiology — causal chain

7. Anatomical Structures Affected

8. Temporal Development

9. Inheritance and Population

10. Diagnostics

11. Outcome/Prognosis

12. Treatment

13. Prevention

14. Other Species / Natural Disease

15. Model Organisms

Mechanistic Model / Interpretation

Evidence Base

Limitations and Knowledge Gaps

Proposed Follow-up Experiments / Actions

Artifacts

Reference Validation

Unresolved references

Term Validation

Terms the report names something else

Terms whose name is worth a second look

Terms named inconsistently

Prefixes with no resolver