Genetic Heterogeneity in Susceptibility to Familial Thyroid Nodular Disease

Nontoxic multinodular goiter (MNG), recently reclassified as thyroid follicular nodular disease (TFND), is a common thyroid disorder with complex and incompletely understood genetic contributors. Although familial aggregation and genetic predisposition have been observed, the underlying molecular mechanisms remain only partially defined.

To identify rare germline genetic variants contributing to familial euthyroid TFND, including families with pedigrees suggestive of autosomal dominant inheritance, using whole-exome sequencing (WES).

WES was performed on germline DNA from 28 affected individuals belonging to eight pedigrees exhibiting TFND. Two analytical approaches were applied, including a cross-pedigree analysis to detect disrupted genes shared across multiple kindreds and kindred-based analyses to identify rare pathogenic variants segregating within individual pedigrees or single affected individuals. Somatic sequencing of four available TFND tissues was also performed to search for second-hit mechanisms or copy number alterations (CNA).

Cross-pedigree analysis identified one gene carrying variants of uncertain significance, which did not emerge as definitive candidates. Pedigree-specific analyses revealed a truncating DICER1 variant in a kindred previously linked to the MNG-1 locus and associated with early disease onset; a heterozygous SLC26A4 variant in only one affected individual from another kindred and loss of heterozygosity in the patient's tissue; and a pathogenic WFS1 variant in one kindred, supporting its previously proposed role as a TFND candidate gene, but requiring further validation. Both germline CNA analysis and targeted PLCB1 screening in all kindreds yielded negative results.

This study highlights the substantial genetic heterogeneity underlying familial TFND. While most kindreds lacked clear monogenic causes, DICER1 explained familial disease in one pedigree, whereas the SLC26A4 findings supported a likely somatic second-hit mechanism in a single affected member of another pedigree without accounting for the familial aggregation. The findings support a multifactorial etiology and suggest that TFND represents a phenotypic manifestation within broader hereditary syndromes. Integrating family-based sequencing with functional validation will be critical to fully delineate pathogenic mechanisms and broaden the spectrum of genes implicated in thyroid nodular disease.