Genetic Heterogeneity in Susceptibility to Familial Thyroid Nodular Disease

Background: 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. Objective: 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). Methods: 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). Results: 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. Conclusions: 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.