Complex Balanced Translocation Disrupting TCF4 and Altering TCF4 Isoform Expression Segregates as Mild Autosomal Dominant Intellectual Disability

ABSTRACT: Mutations of TCF4, which encodes a basic helix-loop-helix transcription factor, cause Pitt-Hopkins syndrome (PTHS) via multiple genetic mechanisms. TCF4 is a complex locus expressing multiple transcripts by alternative splicing and use of multiple promoters. We report a three-generation family segregating mild intellectual disability with an apparently balanced chromosomal translocation t(14;18)(q23.3;q21.2) that we characterized as a complex unbalanced karyotype 46,XY,der(14)del(14)(q23.3q23.3)t(14;18)(q23.3;q21.2)del(18)(q21.2q21.2) del(18)(q21.2q21.2)inv(18)(q21.2q21.2),der(18)t(14 ;18)(q23.3;q21.2) disrupting TCF4. Using whole genome sequencing, transcriptome sequencing, qRT-PCR and nCounter analysis, we characterized the breakpoint junctions from derivative chromosomes and gene expression at the TCF4 locus. Our analyses revealed that family members segregating mild intellectual disability with the complex chromosome aberration had normal expression of genes along chromosomes 14 or 18 and no marked changes in expression of genes other than TCF4. Affected individuals had 12-33 fold higher mRNA levels of TCF4 than did unaffected controls or individuals with PTHS. Increased levels of TCF4 transcript variants originating distal to the translocation breakpoint, not the fusion transcript generated by the derivative chromosome, contributed to this increased. Although validation in additional patients is required, our findings suggest that the dysmorphic features and severe intellectual disability characteristic of PTHS is partially rescued by overexpression of short TCF4 transcripts encoding a nuclear localization signal, a transcription activation domain, and the basic helix-loop-helix domain.

ORGANISM(S): Homo sapiens

PROVIDER: GSE77742 | GEO | 2016/05/31

SECONDARY ACCESSION(S): PRJNA311348

REPOSITORIES: GEO