Fluri R et al., The American Journal of Human Genetics - This episode examines a cohort study of 16 individuals with de novo LDB1 variants that reveals two overlapping but distinct neurodevelopmental phenotypes tied to variant location. Functional assays and Drosophila models demonstrate loss-of-function effects for N-terminal variants and dominant-negative effects for C-terminal variants. Key terms: LDB1, neurodevelopmental disorder, ventriculomegaly, dominant-negative, haploinsufficiency.

Study Highlights:
The authors assembled 16 individuals with de novo LDB1 variants and mapped variants to the N-terminal dimerization domain or the C-terminal LIM interaction domain. In vitro assays showed N-terminal missense variants disrupt homodimerization leading to loss of function, while C-terminal variants impair LHX2 binding and act in a dominant-negative manner. Drosophila knockdown and overexpression corroborated dosage sensitivity and distinct in vivo effects, including rescue by wild-type LDB1 and worsening by C-terminal variants. Clinically, C-terminal LID-affecting variants associate with congenital ventriculomegaly and more frequent extra‑neural anomalies, whereas N-terminal variants tend to cause variable NDD without consistent brain malformations.

Conclusion:
Variant location in LDB1 predicts distinct pathomechanisms and overlapping clinical presentations: N-terminal variants cause haploinsufficiency/loss of function, while C-terminal LID variants act dominant-negatively and are linked to ventriculomegaly and broader organ involvement.

Music:
Enjoy the music based on this article at the end of the episode.

Article title:
De novo variants in LDB1 are linked to distinct neurodevelopmental phenotypes determined by variant location and differing pathomechanisms

First author:
Fluri R

Journal:
The American Journal of Human Genetics

DOI:
10.1016/j.ajhg.2026.05.012

Reference:
Fluri R., Coll-Tané M., Brunet T., et al. De novo variants in LDB1 are linked to distinct neurodevelopmental phenotypes determined by variant location and differing pathomechanisms. The American Journal of Human Genetics. 2026;113:1–15. doi:10.1016/j.ajhg.2026.05.012

License:
This episode is based on an open-access article published under the Creative Commons Attribution 4.0 International License (CC BY 4.0) – https://creativecommons.org/licenses/by/4.0/

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Episode link: https://basebybase.com/episodes/ldb1-variant-location-pathomechanisms

QC:
This episode was checked against the original article PDF and publication metadata for the episode release published on 2026-06-23.

QC Scope:
- article metadata and core scientific claims from the narration
- excludes analogies, intro/outro, and music
- transcript coverage: Audited sections describing LDB1 structure (DD and LID), variant spectrum (N-terminal vs C-terminal), two mechanisms (haploinsufficiency vs dominant-negative), cellular assays (protein levels, ubiquitination, aggregates), LDB1-LHX2 interactions, Drosophila chi model (dosage sensitivity, rescue/toxicity, sleep), and cli
- transcript topics: LDB1 structure and domains (DD and LID); Variant spectrum across LDB1 (N-terminal vs C-terminal); Mechanisms: haploinsufficiency and dominant-negative effects; Cellular assays: protein stability, ubiquitination, aggregates; LDB1 interactions: dimerization and LHX2 binding; Drosophila model chi (chip) dosage sensitivity and experiments

QC Summary:
- factual score: 9/10
- metadata score: 10/10
- supported core claims: 7
- claims flagged for review: 1
- metadata checks passed: 4
- metadata issues found: 0

Metadata Audited:
- article_doi
- article_title
- article_journal
- license

Factual Items Audited:
- Two distinct LDB1-related neurodevelopmental phenotypes based on variant location (N-terminal LoF/haploinsufficiency vs C-terminal dominant-negative)
- N-terminal DD missense variants Arg121Trp and Arg193Trp impair LDB1 homodimerization (loss of function)
- C-terminal LID-disrupting variants impair LDB1-LHX2 interaction and act in a dominant-negative manner
- C-terminal frameshift variants increase LDB1 protein levels and form nuclear aggregates via altered ubiquitination
- N-terminal DD variants can decrease protein stability in some contexts
- Co-expression assays show dominant-negative interference of C-terminal variants with wild-type LDB1/LHX2 interactions

QC Flagged Items (audited and not fully supported):
- Core claim uncertain: The Arg181Gln variant remains a VUS with uncertain functional effect.

QC result: Warning. Items above were flagged during automated QC; the editorial team reviewed them before release.