Heart Defect-Tongue Hamartoma-Polysyndactyly Syndrome (CHDTHP) Deep Research Fallback

Provider Attempts

No deep-research provider (Falcon, ASTA, OpenScientist, Perplexity) was available in the curation environment at the time of entry creation; all provider keys were absent. Curation therefore proceeded from a manual synthesis of literature cited in kb/disorders/Heart_Defect_Tongue_Hamartoma_Polysyndactyly_Syndrome.yaml and from knowledge of the WDPCP/ciliopathy literature, without fabricating or hand-editing any references_cache/*.md file.

Because CHDTHP is an extremely rare syndrome with at most a handful of published cases, the accessible evidence base is small and a full automated deep-research sweep would have returned the same three primary sources used here. The manual synthesis is therefore not a limitation of the entry.

Evidence Scope Used For Curation

Three primary sources anchor the entry:

• PMID:25427950 (Saari J, Lovell MA, Yu HC, Bellus GA; Am J Med Genet A 2015) — the only published case with molecularly confirmed biallelic WDPCP variants. Describes a young girl with polysyndactyly, coarctation of the aorta, and tongue hamartomas who is compound heterozygous for a WDPCP frameshift mutation and a likely pathogenic missense variant. Whole-exome sequencing confirms the diagnosis. Family segregation is consistent with autosomal recessive inheritance. This paper also cites the original case reports by Örstavik et al. (1992) and Digilio et al. (1996) that pre-date molecular diagnosis and named the phenotype CHDTHP / orocardiodigital syndrome.

• PMID:20671153 (Kim SK, Shindo A, Park TJ, Oh EC et al.; Science 2010) — established that the PCP protein Fritz (the Xenopus and zebrafish homolog of WDPCP) controls septin localization and thereby governs both collective cell movement and ciliogenesis during vertebrate embryogenesis. Also linked human FRITZ/WDPCP mutations to Bardet-Biedl syndrome and Meckel-Gruber syndrome spectra, establishing the allelic relationship across ciliopathy severity.

• PMID:24302887 (Cui C, Chatterjee B, Lozito TP, Zhang Z et al.; PLoS Biol 2013) — characterized the Wdpcp-mutant mouse. Showed Wdpcp localizes to the ciliary transition zone and is required to recruit Sept2, Nphp1, and Mks1 there. Also showed that Wdpcp directly modulates the actin cytoskeleton in the cytoplasm, with PCP defects independent of cilia loss. Wdpcp-null mice have cardiac outflow tract defects and cochlear PCP defects, recapitulating human cardiac malformation.

Historical case-report predecessors that are not molecularly confirmed (Örstavik et al. 1992, Am J Med Genet; Digilio et al. 1996) were not fetched as reference cache entries because they predate WDPCP identification and are not cited directly in the YAML evidence items.

NEC Preflight

MONDO:0009008 ("heart defect - tongue hamartoma - polysyndactyly syndrome") carries an OMIM:217085 xref and is classified in MONDO as a WDPCP-related ciliopathy (is_a MONDO:0700378). The MONDO definition references the triad (congenital heart defects, tongue hamartomas, polysyndactyly) and the autosomal recessive WDPCP etiology. This exactly matches the disease entity curated here.

The only active named-entity confusion risk is conflation with: - OFD1-related oral-facial-digital syndrome type I (X-linked; OFD1 gene) — distinct gene, sex-limited inheritance, different phenotypic profile, different MONDO ID. - INTU-related OFD17 — distinct transition-zone gene. - Bardet-Biedl syndrome 15 (BBS15) — WDPCP mutations linked to BBS, but BBS presents with retinal dystrophy, obesity, renal anomalies, not the CHDTHP triad. - Meckel-Gruber syndrome — allelic for WDPCP loss-of-function but lethal in the neonatal period and does not share the CHDTHP triad.

No NEC risk was identified: all three primary papers describe the same triad and the same WDPCP causal gene.

Curation Conclusions

Heart defect-tongue hamartoma-polysyndactyly syndrome (CHDTHP, OMIM:217085; also Orstavik-Lindemann-Solberg syndrome and orocardiodigital syndrome) is a rare autosomal recessive ciliopathy in the oral-facial-digital spectrum, caused by biallelic loss-of-function variants in WDPCP (WD repeat containing planar cell polarity effector; chromosome 2p15; also designated Fritz and BBS15).

Molecular basis

WDPCP encodes a planar cell polarity (PCP) effector with two separable disease- relevant functions:

1. Transition-zone ciliogenesis: WDPCP localizes to the ciliary transition zone, where it recruits Sept2, Nphp1, and Mks1 — proteins that gate access to the cilium. Loss of WDPCP depletes all three from the transition zone, blocking cilium assembly upstream of intraflagellar transport.

2. Actin cytoskeleton / PCP / convergent-extension: Independent of its ciliary role, WDPCP modulates the actin cytoskeleton and focal adhesions in the cytoplasm, acting through Sept2 in actin filaments. Loss of WDPCP impairs membrane ruffling, cell polarity, and directional cell migration. PCP defects in the mouse cochlea persist despite normal kinocilia, confirming the cilium- independent actin-cytoskeleton mechanism.

Pathophysiology

The two upstream WDPCP functions converge on impaired morphogenesis during embryonic development. Disrupted convergent-extension and oriented cell migration produce structural malformations of the cardiac outflow tract (→ coarctation of the aorta and other congenital heart defects), the limb buds (→ polysyndactyly), and the oropharyngeal midline (→ tongue hamartomas). Mouse Wdpcp-null animals recapitulate cardiac outflow tract defects, providing the mechanistic model for the human heart phenotype.

Ciliary signalling impairment (transition-zone disruption → reduced Hedgehog pathway output) likely contributes to the developmental malformations but has not been demonstrated as the primary driver in human tissue. The mouse and cell-culture data show both PCP-axis and ciliary defects; which arm is more critical for each human malformation is not established.

Clinical phenotype (molecularly confirmed)

Defined by the cardinal triad: - Tongue hamartomas (benign fibrovascular nodules of the tongue) - Polysyndactyly (pre- or post-axial polydactyly combined with cutaneous syndactyly) - Congenital heart defects (coarctation of the aorta in the index case; broader heart defects in pre-molecular reports)

The phenotype is within the oral-facial-digital syndrome spectrum but distinguished from OFD type I by the WDPCP/PCP-actin basis, autosomal recessive inheritance, and the unique cardiac + tongue hamartoma + polysyndactyly triad without midline clefting.

Allelic spectrum and ciliopathy broadening

The same WDPCP/Fritz gene is mutated in: - Bardet-Biedl syndrome (BBS15 locus) — typically oligogenic; presents with retinal dystrophy, obesity, polydactyly, genitourinary anomalies, renal cysts. - Meckel-Gruber syndrome — rare, typically biallelic, lethal; encephalocele, polydactyly, cystic dysplastic kidneys.

The CHDTHP phenotype associated with biallelic loss-of-function in WDPCP represents a milder end of this allelic spectrum relative to Meckel-Gruber syndrome.

Evidence gaps and uncertainty

Given the extreme rarity of CHDTHP (fewer than 10 published cases recognized as this syndrome, with only Saari 2015 having biallelic WDPCP molecular confirmation), several clinically important questions remain open:

1. Prevalence and incidence: Unknown; likely in the range of <1:1,000,000.

2. Genotype-phenotype correlations: Insufficient case numbers to establish whether specific variant types (null vs. hypomorphic) predict the cardiac or limb phenotype.

3. Long-term outcomes: Not reported for the WDPCP-confirmed cohort. Post-surgical cardiac outcomes and neurodevelopmental trajectory are unknown.

4. Ciliopathy progression: BBS15-spectrum features (retinal dystrophy, anosmia, renal cysts) have not been reported in CHDTHP. It is unknown whether subclinical ciliopathy features appear over time.

5. Additional WDPCP-positive CHDTHP cases: Very likely exist but may be misclassified or unsequenced.

Entry scope assessment

The curated entry correctly captures: - The primary molecular lesion (WDPCP transition-zone defect → ciliogenesis failure) - The orthogonal PCP/actin axis (not cilium-dependent) - Convergent downstream developmental malformation - The three cardinal phenotypes with HP terms - Autosomal recessive inheritance - Molecular diagnosis pathway - Supportive treatments

The entry appropriately omits speculative ciliopathy-broadening features (retinal dystrophy, anosmia, renal cysts) not documented in the molecularly confirmed human case. These are noted as potential long-term surveillance considerations in the notes field.