Incomplete partition type II in its various manifestations: isolated, in association with EVA, syndromic, and beyond; a multicentre international study.

PURPOSE: Incomplete partition type II (IP-II) is characterized by specific histological features and radiological appearance. It may occur in isolation or in association with an enlarged vestibular aqueduct (EVA). Among those with IP-II and EVA, a subset has a diagnosis of Pendred syndrome. This study aimed to explore the prevalence of isolated IP-II, IP-II with EVA, and cases with a genetic or syndromic basis in our cohort. METHODS: From a large, multicentre database of dysplastic cochleae (446 patients, 892 temporal bones), those with imaging features of IP-II were examined in detail, including whether there was a genetic or syndromic association. RESULTS: A total of 78 patients with IP-II were identified. Among these, 55 patients had bilateral IP-II and EVA (only 12 with typical Mondini triad), 8 with bilateral IP-II and normal VA, 2 with bilateral IP-II and unilateral EVA, and 13 with unilateral IP-II (9 with unilateral EVA). Among the group with bilateral IP-II and bilateral EVA in whom genetic analysis was available, 14 out of 29 (48%) had SLC26A4 mutations and a diagnosis of Pendred syndrome, 1 had a FOXI1 mutation, and a few other genetic abnormalities; none had KCNJ10 pathogenic variants. CONCLUSION: Bilateral IP-II-bilateral EVA may be seen in the context of Pendred syndrome (SLC26A4 or FOXI1 mutations) but, in the majority of our cohort, no genetic abnormalities were found, suggesting the possibility of unknown genetic associations. IP-II in isolation (without EVA) is favored to be genetic when bilateral, although the cause is often unknown.

Variability in Inner Ear Morphology Among a Family With Pendred Syndrome Due to a SLC26A4 Gene Variant.

OBJECTIVES: Pendred syndrome, an autosomal recessive disorder, is often associated with pathogenic variants of the SLC26A4 gene that encodes the pendrin protein. Given its autosomal recessive inheritance, tracing the family history and screening siblings become crucial once a diagnosis of Pendred syndrome is confirmed. This case report aims to underscore the variability in inner ear morphology within a family diagnosed with Pendred syndrome, all carrying the same SLC26A4 gene mutation. METHODS: A chart review and a review of the literature. RESULTS: We present a family of 4, all of whom possess sensorineural hearing loss due to the same homozygous SLC26A4 variant c.919-2A>G. Intriguingly, clinical manifestations, especially inner ear deformities, displayed variability among family members. Notably, 1 family member exhibited a normal cochleovestibular structure morphology, which was rarely reported in the literature. CONCLUSIONS: This report highlights the significance of genetic testing and familial consultation when a proband exhibits typical Pendred syndrome symptoms. It also underscores that the inner ear morphology can exhibit variability among family members, even with the same homozygous SLC26A4 variant.

The BRAF V600E Mutation and Clinicopathological Changes Among Patients With Hashimoto Thyroiditis, Papillary Thyroid Carcinoma With Hashimoto Thyroiditis, and Nodular Goiter.

The study aimed to investigate the BRAF V600E mutation and clinicopathological changes among patients with Hashimoto thyroiditis (HT), papillary thyroid carcinoma (PTC) with Hashimoto thyroiditis (HT), or nodular goiter (NG). A total of 87 patients with the BRAF V600E mutation who were diagnosed with HT (including with hyperplasia dysplasia), PTC with HT, and PTC with NG were enrolled. Clinical data, concentrations of antithyroglobulin antibodies (TGAb) and thyroid microsomal antibodies (TMAb) in the serum thyroid-function levels, and the result presence of the BRAF V600E mutation were retrospectively analyzed. There were significant differences in the BRAF V600E mutation rates between the HT and PTC with HT groups ( P <0.05) and the HT and PTC with NG groups ( P <0.05), whereas no significant difference was found between the PTC with HT and PTC with NG groups. There was no difference in incidences of PTC between HT with elevated TGAb and TMAb group and those with baseline levels. The incidence of multifocal PTC was higher in the PTC with HT group; however, the difference was not significant. Our findings documented that BRAF mutation distinguished between the benign HT and the malignant PTC groups. The serum levels of TGAb and TMAb autoantibodies did not directly correlate with PTC in the background of HT. HT and NG may similarly contribute to the pathogenesis of PTC.

Functional variants in a TTTG microsatellite on 15q26.1 cause familial nonautoimmune thyroid abnormalities.

Insufficient thyroid hormone production in newborns is referred to as congenital hypothyroidism. Multinodular goiter (MNG), characterized by an enlarged thyroid gland with multiple nodules, is usually seen in adults and is recognized as a separate disorder from congenital hypothyroidism. Here we performed a linkage analysis of a family with both nongoitrous congenital hypothyroidism and MNG and identified a signal at 15q26.1. Follow-up analyses with whole-genome sequencing and genetic screening in congenital hypothyroidism and MNG cohorts showed that changes in a noncoding TTTG microsatellite on 15q26.1 were frequently observed in congenital hypothyroidism (137 in 989) and MNG (3 in 33) compared with controls (3 in 38,722). Characterization of the noncoding variants with epigenomic data and in vitro experiments suggested that the microsatellite is located in a thyroid-specific transcriptional repressor, and its activity is disrupted by the variants. Collectively, we presented genetic evidence linking nongoitrous congenital hypothyroidism and MNG, providing unique insights into thyroid abnormalities.

NKX2-1 gene is targeted by H19 lncRNA and is found to be overexpressed in benign nodular goiter tissues.

OBJECTIVE: Nodular goiter may increase the risk of thyroid cancer, but the genetic factors contributing to nodular goiter are not well understood. There is an overexpression of H19 lncRNA in goiter tissue and its target remains unknown. In this study, we attempted to identify a new target for H19 in the context of goiter development. METHODS: Using interaction energy calculations, the interaction between NKX2-1 mRNA and H19 lncRNA was examined. Putative microRNAs were found at the H19 lncRNA target site with the highest affinity for NKX2-1. RNAseq data was analyzed to determine the tissue specificity of gene expression. Samples were taken from 18 goiter and 18 normal tissues during thyroidectomy. The expression of NKX2-1 was determined by RT-qPCR using specific primers. RESULTS: The interaction between NKX2-1 and H19 was characterized by six local base-pairing connections, with a maximum energy of -20.56 kcal/moL. Specifically, the sequence that displayed the highest affinity for binding with H19 overlapped with the binding site of has-miR-1827 to NKX2-1. It was found that NKX2-1 is exclusively co-expressed with H19 in normal thyroid tissue. As compared to adjacent normal tissues, nodular goiter tissues have a significant overexpression of NKX2-1 (relative expression = 1.195, p =  0.038). CONCLUSION: NKX2-1 has been identified as the putative target of H19 lncRNA, which is overexpressed in nodular goiter tissues significantly.

Prevalence of DICER1 variants in large multinodular goiter: thyroid function, clinical and imaging characteristics.

Objective: Mutations in DICER1 are found in differentiated thyroid carcinoma (DTC) and in multinodular goiter (MNG) at a younger age with other tumors, which characterizes DICER1 syndrome. DICER1 is one driver to DTC; however, it is also found in benign nodules. We speculated that patients with mutations in DICER1 may present long-lasting MNG. Our aim was to investigate the frequency of DICER1 variants in patients with MNG. Subjects and methods: Patients who submitted to total thyroidectomy due to large MNG with symptoms were evaluated. DICER1 hotspots were sequenced from thyroid nodule samples. To confirm somatic mutation, DNA from peripheral blood was also analyzed. Results: Among 715 patients, 154 were evaluated with 56.2 ± 12.3 years old (28-79) and the thyroid volume was 115.7 ± 108 mL (16.2-730). We found 11% with six DICER1 variations in a homo or heterozygous state. Only rs12018992 was a somatic DICER1 variant. All remaining variants were synonymous and likely benign, according to the ClinVar database. The rs12018992 was previously described in an adolescent with DTC, measuring 13 mm. There were no significant differences according to gender, familial history of goiter, age, thyroid volume, TSH and TI-RADS classification between DICER1 carriers. Free T4 were lower in patients with DICER1 polymorphisms (13.77 ± 1.8 vs. 15.44 ± 2.4 pmol/L, p = 0.008), regardless of TSH levels. Conclusion: We conclude that germline DICER1 variants can be found in 11% of large goiters but no second-hit somatic mutation was found. DICER1 is one driver to thyroid lesion and a second-hit event seems unnecessary in the MNG development.

Analysis of clinical characteristics of thyroid phenotype in Pendred syndrome based on multiple databases.

OBJECTIVE: This study aimed to provide statistical data support for the development of thyroid phenotype-related follow-up and reference for follow-up duration and project selection by analyzing the clinical characteristics of thyroid phenotype in Pendred syndrome (PDS) based on multiple databases. MATERIALS AND METHODS: PDS-related pathogenic or possibly/pathogenic mutations were searched by Deafness Variation Database (DVD), ClinVar, and PubMed databases, the mutation sites were counted and the characteristics and thyroid phenotypes were analyzed. RESULTS: The median age of hearing phenotype onset in PDS cases reported in multiple databases was 1.0 (1.0, 2.0) years, the median age of thyroid phenotype onset was 14.5 (5.8, 21.0) years, and the median age that thyroid phenotype was more delayed than hearing phenotype was 10.0 (4.0, 17.0) years. There were significant differences in the distribution of onset time between the two phenotypes (Z=-4.560, p<0.01). In these patients, the positive rates of goiter, thyroid nodules, abnormal thyroid function, and perchlorate discharge test (PDT) were 78%, 78%, 69%, and 78%, respectively. Moreover, the number of thyroid phenotype-positive items in the genotype group with frameshift mutation was not significantly higher than that in the group without frameshift mutation (Z=-1.452, p=0.147). CONCLUSIONS: The early missed diagnosis of PDS may be due to the late onset of thyroid phenotype and the non-100% positive rate of examination items. Therefore, multi-item follow-up of the thyroid gland into adulthood will benefit patients. At present, the relationship between genotype and phenotype is still unclear, and prognosis cannot be determined according to genotype.

Asymmetric pendrin homodimer reveals its molecular mechanism as anion exchanger.

Pendrin (SLC26A4) is an anion exchanger expressed in the apical membranes of selected epithelia. Pendrin ablation causes Pendred syndrome, a genetic disorder associated with sensorineural hearing loss, hypothyroid goiter, and reduced blood pressure. However its molecular structure has remained unknown, limiting our understanding of the structural basis of transport. Here, we determine the cryo-electron microscopy structures of mouse pendrin with symmetric and asymmetric homodimer conformations. The asymmetric homodimer consists of one inward-facing protomer and the other outward-facing protomer, representing coincident uptake and secretion- a unique state of pendrin as an electroneutral exchanger. The multiple conformations presented here provide an inverted alternate-access mechanism for anion exchange. The structural and functional data presented here disclose the properties of an anion exchange cleft and help understand the importance of disease-associated variants, which will shed light on the pendrin exchange mechanism.

[DICER1 syndrome: clinical variety endocrine manifestations and features of diagnostics].

DICER1 syndrome is a rare genetic disorder with the progressive development of malignant and non-malignant diseases in childhood. The cause of this syndrome is a dusfunction of the endoribonuclease DICER, which plays an important role in the processing of microRNAs with subsequent regulation of the control of the expression of oncogenes and tumor suppressor genes. Clinical manifestations of dyseropathies is very different and may include both endocrine manifestations - multinodular goiter, differentiated thyroid cancers, ovarian stromal tumors, pituitary blastoma, and non-endocrine formations - pleuropulmonary blastoma, cystic nephroma, pineoblastoma. The presence of somatic mutations of the DICER1 gene is a resultant stage in the pathogenesis of dyseropathies, determining the further path of oncogenesis. At present, DICER1 syndrome is diagnosed extremely rarely, which leads to late detection of the components of the disease in the patient, late diagnosis of neoplasms, lack of family counseling. Diagnosis at the early stages of the disease, the development of screening programs for the management of these patients allows minimizing the risks of developing more malignant, aggressive forms of the disease.

Histopathological Features of Pendred Syndrome Thyroids Align with Differences in the Expression of Thyroid-Specific Markers, Apical Iodide Transporters, and Ciliogenesis Process.

Pendred syndrome (PDS) is an autosomal recessive disorder caused by mutations in the gene that encodes pendrin. Pendred thyroid tissue is supposedly altered by the absence of functional pendrin, but it is still unknown whether other iodide exchangers could compensate for the loss of the protein. Moreover, we have recently described that primary cilium, a conserved structure present at the apical surface of normal follicular cells, suffers different alterations in functional thyroid diseases. We aimed (1) to better understand the histopathological changes experienced by PDS thyroids, (2) to analyze the expression of different thyroid-specific genes and alternative iodide transporters and, finally, (3) to determine whether those changes may alter the morphological pattern of primary cilia in follicular cells. Thyroid samples from a series of four PDS patients were analyzed by immunohistochemistry, double immunofluorescence, and morphometry to evaluate changes in primary cilia frequency and length. We found thyroid follicular nodular disease in all PDS thyroids, frequently in association with follicular adenomas. There were only slight changes in the expression of thyroid-specific markers. Although no positivity for pendrin was found, cytoplasmic immunostaining for ANO-1, CLC-5, and CFTR was stronger in diffuse hyperplastic areas when compared to areas with highly cellular follicular nodules (HCFNs). HCFNs and follicular adenomas always showed diminished ciliary frequency and length. Our results suggest a direct relationship between the absence of functional pendrin and the loss of the normal thyroid architecture in PDS patients, which was also accompanied by differences in the expression of specific immunohistochemical markers and altered ciliogenesis. The present data may help the pathologist in screening for PDS.

Ultrasound features of multinodular goiter in DICER1 syndrome.

DICER1 syndrome is caused by germline pathogenic mutations in the DICER1 gene. Multinodular goiter (MNG) is a common clinical feature of DICER1 syndrome in children and adults. The aim of this study was to determine the ultrasound (US) characteristics of MNG in patients with DICER1 syndrome. This retrospective study evaluated thyroid US in patients with DICER1 germline mutations (DICER1mut+) performed between 2011 and 2018 at a single center by the same pediatric endocrinologist, and the images were re-examined by an independent pediatric radiologist from another academic center. Patients < 18 years with DICER1mut+ and DICER1mut+ parents without previous thyroidectomy were included. Ultrasound phenotypes of MNG in the setting of DICER1 mutations were compared with known US features of thyroid malignancy. Thirteen DICER1mut+ patients were identified (10 children, 3 adults). Three children had a normal thyroid US; therefore, thyroid abnormalities were assessed in seven children and three adults. In both children and adults, multiple (≥ 3) mixed (cystic/solid) nodules predominated with single cystic, single cystic septated and single solid nodules, occasionally with a "spoke-like" presentation. All solid lesions were isoechogenic, and in only one with multiple solid nodules, intranodular blood flow on power/color Doppler was observed. Remarkably, macrocalcifications were present in all three adults. The spectrum of ultrasonographic findings of MNG in DICER1mut+ patients is characteristic and largely distinct from typical features of thyroid malignancy and therefore should inform physicians performing thyroid US of the possible presence of underlying DICER1 syndrome.

SLC26A4 mutation in Pendred syndrome with hypokalemia: A case report.

RATIONALE: Pendred syndrome is an autosomal recessive disorder characterized by sensorineural hearing loss, inner ear malformations, goiter, and abnormal organification of iodide. It is caused by mutations in SLC26A4 gene, which encodes pendrin (a transporter of chloride, bicarbonate, and iodide). Pendred syndrome is a common cause of syndromic deafness, but the metabolic abnormalities it causes are often overlooked. Here, we report the case of a patient diagnosed with Pendred syndrome with hypokalemia. PATIENT CONCERNS: A 53-year-old deaf-mute woman was hospitalized due to severe limb asthenia. The emergency examination showed that her blood potassium level was 1.8 mmol/L. DIAGNOSES: Through the genetic test, we found a mutation of SLC26A4 gene in NM_000441: c.2027T>A, p.L676Q, as well as the SLC26A4 exon 5-6 deletion. These genetic variations pointed to Pendred syndrome (an autosomal recessive disorder that mainly affects the inner ear, thyroid, and kidney) which is a common cause of syndromic deafness. INTERVENTIONS: The patient was treated with potassium supplements and screened for the cause of hypokalemia. OUTCOMES: The patient was discharged after her potassium levels rose to the normal range. LESSONS: Patients with Pendred syndrome may also have certain metabolic abnormalities; thus, more attention should be paid to them during clinical diagnosis.

Differential gene expression profile of multinodular goiter.

INTRODUCTION: The goiter, a neglected heterogeneous molecular disease, remains a major indication for thyroidectomies in its endemic regions. OBJECTIVES: This study analyzed differential gene expression in surgical specimens diagnosed with multi nodular and compared the data to that of thyroid tissue without multinodular goiter from patients undergoing thyroidectomy in Manaus-AM, Brazil using RNA-seq technology. METHODOLOGY: The transcriptome information of the surgical specimen fragments with and without multinodular goiter was accessed by Illumina HiSeq 2000 New Generation Sequencing (NGS) using the RNA-seq NEBNext® Ultra™ RNA Library Prep Kit for Illumina®-#E7530L protocol and differential gene expression analysis. RESULTS: Differences were found between the gene expression profiles of the diseased tissues and those of the healthy control tissues; at least 70 genes were differentially expressed. The HOTS gene was expressed only in multinodular goiter tissues (p < 0.05). CONCLUSION: These results demonstrate that the gene expression profile of multinodular goiter is pro-tumoral and that HOTS can play a central role in multinodular goiter development.

Gene expression profile in functioning and non-functioning nodules of autonomous multinodular goiter from an area of iodine deficiency: unexpected common characteristics between the two entities.

PURPOSE: Toxic multinodular goiter is a heterogeneous disease associated with hyperthyroidism frequently detected in areas with deficient iodine intake, and functioning and non-functioning nodules, characterized by increased proliferation but opposite functional activity, may coexist in the same gland. To understand the distinct molecular pathology of each entity present in the same gland, the gene expression profile was evaluated by using the Affymetrix technology. METHODS: Total RNA was extracted from nodular and healthy tissues of two patients and double-strand cDNA was synthesized. Biotinylated cRNA was obtained and, after chemical fragmentation, was hybridized on U133A and B arrays. Each array was stained and the acquired images were analyzed to obtain the expression levels of the transcripts. Both functioning and non-functioning nodules were compared versus healthy tissue of the corresponding patient. RESULTS: About 16% of genes were modulated in functioning nodules, while in non-functioning nodules only 9% of genes were modulated with respect to the healthy tissue. In functioning nodules of both patients and up-regulation of cyclin D1 and cyclin-dependent kinase inhibitor 1 was observed, suggesting the presence of a possible feedback control of proliferation. Complement components C1s, C7 and C3 were down-regulated in both types of nodules, suggesting a silencing of the innate immune response. Cellular fibronectin precursor was up-regulated in both functioning nodules suggesting a possible increase of endothelial cells. Finally, Frizzled-1 was down-regulated only in functioning nodules, suggesting a role of Wnt signaling pathway in the proliferation and differentiation of these tumors. None of the thyroid-specific gene was deregulated in microarray analysis. CONCLUSION: In conclusion, the main finding from our data is a similar modulation for both kinds of nodules in genes possibly implicated in thyroid growth.

Pendred Syndrome, or Not Pendred Syndrome? That Is the Question.

Pendred syndrome (PDS) is the most common form of syndromic Hearing Loss (HL), characterized by sensorineural HL, inner ear malformations, and goiter, with or without hypothyroidism. SLC26A4 is the major gene involved, even though ~50% of the patients carry only one pathogenic mutation. This study aims to define the molecular diagnosis for a cohort of 24 suspected-PDS patients characterized by a deep radiological and audiological evaluation. Whole-Exome Sequencing (WES), the analysis of twelve variants upstream of SLC26A4, constituting the "CEVA haplotype" and Multiplex Ligation Probe Amplification (MLPA) searching for deletions/duplications in SLC26A4 gene have been carried out. In five patients (20.8%) homozygous/compound heterozygous SLC26A4 mutations, or pathogenic mutation in trans with the CEVA haplotype have been identified, while five subjects (20.8%) resulted heterozygous for a single variant. In silico protein modeling supported the pathogenicity of the detected variants, suggesting an effect on the protein stabilization/function. Interestingly, we identified a genotype-phenotype correlation among those patients carrying SLC26A4 mutations, whose audiograms presented a characteristic slope at the medium and high frequencies, providing new insights into PDS. Finally, an interesting homozygous variant in MYO5C has been identified in one patient negative to SLC26A4 gene, suggesting the identification of a new HL candidate gene.

Prevalence of Pathogenic Germline DICER1 Variants in Young Individuals Thyroidectomised Due to Goitre - A National Danish Cohort.

Introduction: DICER1 syndrome encompasses a variety of benign and malignant manifestations including multinodular goitre, which is the most common manifestation among individuals carrying pathogenic DICER1 variants. This is the first study estimating the prevalence of pathogenic DICER1 variants in young individuals with multinodular goitre. Methods: Danish individuals diagnosed with nodular goitre based on thyroidectomy samples in 2001-2016 with the age limit at time of operation being ≤ 25 years were offered germline DICER1 gene testing. Results: Six of 46 individuals, 13% (CI [3.3;22.7], p <0.05), diagnosed with nodular goitre on the basis of thyroidectomy samples under the age of 25 years had pathogenic germline variants in DICER1. They were found in different pathoanatomical nodular goitre cohorts i.e. nodular goitre (n=2), colloid nodular goitre (n=3) and hyperplastic nodular goitre (n=1). Conclusions: We recommend referral of patients thyroidectomised due to goitre aged <21 years and patients thyroidectomised due to goitre aged <25 years with a family history of goitre to genetic counselling. Patients of all ages thyroidectomised due to goitre, who are affected by another DICER1 manifestation should be referred to genetic counselling.

Transcriptomic Analysis Reveals an Altered Hcy Metabolism in the Stria Vascularis of the Pendred Syndrome Mouse Model.

Purpose: Slc26a4-/- mice exhibit severer defects in the development of the cochlea and develop deafness, while the underlying mechanisms responsible for these effects remain unclear. Our study was to investigate the potential mechanism linking SLC26A4 deficiency to hearing loss. Materials and Methods: RNA sequencing was applied to analyze the differential gene expression of the stria vascularis (SV) from wildtype and Slc26a4-/- mice. GO and KEGG pathway analysis were performed. Quantitative RT-PCR was applied to validate the expression of candidate genes affected by Slc26a4. ELISA and immunofluorescence technique were used to detect the homocysteine (Hcy) level in serum, brain, and SV, respectively. Results: 183 upregulated genes and 63 downregulated genes were identified in the SV associated with Slc26a4 depletion. Transcriptomic profiling revealed that Slc26a4 deficiency significantly affected the expression of genes associated with cell adhesion, transmembrane transport, and the biogenesis of multicellular organisms. The SV from Slc26a4-/- mice exhibited a higher expression of Bhmt mRNAs, as well as altered homocysteine (Hcy) metabolism. Conclusions: The altered expression of Bhmt results in a dramatic change in multiple biochemical reactions and a disruption of nutrient homeostasis in the endolymph which may contribute to hearing loss of Slc26a4 knockout mouse.

A Genome-First Approach to Characterize DICER1 Pathogenic Variant Prevalence, Penetrance, and Phenotype.

Importance: Genetic disorders are historically defined through phenotype-first approaches. However, risk estimates derived from phenotype-linked ascertainment may overestimate severity and penetrance. Pathogenic variants in DICER1 are associated with increased risks of rare and common neoplasms and thyroid disease in adults and children. This study explored how effectively a genome-first approach could characterize the clinical traits associated with germline DICER1 putative loss-of-function (pLOF) variants in an unselected clinical cohort. Objective: To examine the prevalence, penetrance, and phenotypic characteristics of carriers of germline DICER1 pLOF variants via genome-first ascertainment. Design, Setting, and Participants: This cohort study classifies DICER1 variants in germline exome sequence data from 92 296 participants of the Geisinger MyCode Community Health Initiative. Data for each MyCode participant were used from the start of the Geisinger electronic health record to February 1, 2018. Main Outcomes and Measures: Prevalence of germline DICER1 variation; penetrance of malignant tumors and thyroid disease in carriers of germline DICER1 variation; structured, manual review of electronic health records; and DICER1 sequencing of available tumors from an associated cancer registry. Results: A total of 92 296 adults (mean [SD] age, 59 [18] years; 98% white; 60% female) participated in the study. Germline DICER1 pLOF variants were observed in 1 in 3700 to 1 in 4600 participants, more than double the expected prevalence. Malignant tumors (primarily thyroid carcinoma) were observed in 4 of 25 participants (16%) with DICER1 pLOF variants, which is comparable (by 50 years of age) to the frequency of neoplasms in the largest registry- and clinic-based (phenotype-first) DICER1 studies published to date. DICER1 pLOF variants were significantly associated with risks of thyroidectomy (odds ratio [OR], 6.0; 95% CI, 2.2-16.3; P = .007) and thyroid cancer (OR, 9.2; 95% CI, 2.1-34.7; P = .02) compared with controls, but there was not a significant increase in the risk of goiter (OR, 1.8; 95% CI, 0.7-4.9). A female patient in her 80s who was a carrier of a germline DICER1 hotspot variant was apparently healthy on electronic health record review. The term DICER1 did not appear in any of the medical records of the 25 participants with a pLOF DICER1 variant, even in those affected with a known DICER1-associated tumor or thyroid phenotype. Conclusions and Relevance: This cohort study was able to ascertain individuals with germline DICER1 variants based on a genome-first approach rather than through a previously established DICER1-related phenotype. Use of the genome-first approach may complement more traditional approaches to syndrome delineation and may be an efficient approach for risk estimation.