Citations

ABSTRACT Background Li Fraumeni syndrome (LFS) is a hereditary multi‐cancer syndrome caused by alterations in TP53 (MIM# 151623). Next generation sequencing (NGS) allows for the detection of TP53 variants at lower variant allele frequencies (VAFs). A TP53 variant with a VAF < 50% may represent mosaic LFS, aberrant clonal expansion (ACE), or possible circulating tumor DNA. Differentiation among these conditions is important for optimal patient management. Methods Genetic testing was performed using a custom gene panel, with an average read depth of 350× (range 166–553×). DNA extracted from four different tissues (blood, saliva, cultured skin fibroblasts, and colon) was sequenced. Results Here, we describe an adult female patient with a history of an adrenocortical neoplasm and osteosarcoma, diagnosed at 2 and 16 years of age, respectively. Testing of peripheral blood identified a pathogenic TP53 variant, c.733G>A, p.(Gly245Ser) (NM_000546.6); however, subsequent in vitro fertilization with preimplantation genetic testing for monogenic disorders (PGT‐M) did not identify this TP53 variant in any of nine embryos tested. Testing for possible mosaicism in the proband was performed on four different specimens, revealing variable VAFs of the TP53 variant (saliva: 44%; blood: 31%; cultured skin fibroblasts: 18%; and colon tissue: 9%). These results suggest a post‐zygotic event, consistent with mosaic LFS rather than ACE. Conclusion This case highlights the complexity of interpreting mosaic variants in the TP53 gene, and we propose a testing algorithm to aid in the delineation of this phenomenon when relaying cancer and reproductive risk information in the context of mosaicism.

Conditions related to cardiometabolic disease, including metabolic syndrome and type 2 diabetes, are common among men with Klinefelter syndrome (KS). The molecular mechanisms underlying this aberrant metabolism in KS are largely unknown, although there is an assumption that chronic testosterone deficiency plays a role. This cross-sectional study compared plasma metabolites in 31 pubertal adolescent males with KS to 32 controls of similar age (14 ± 2 years), pubertal stage, and body mass index z -score of 0.1 ± 1.2 and then between testosterone-treated ( n = 16) and untreated males with KS. The plasma metabolome in males with KS was distinctly different from that in controls, with 22% of measured metabolites having a differential abundance and seven metabolites nearly completely separating KS from controls (area under the curve > 0.9, P < 0.0001). Multiple saturated free fatty acids were higher in KS, while mono- and polyunsaturated fatty acids were lower, and the top significantly enriched pathway was mitochondrial β-oxidation of long-chain saturated fatty acids (enrichment ratio 16, P < 0.0001). In contrast, there were no observed differences in metabolite concentrations between testosterone-treated and untreated individuals with KS. In conclusion, the plasma metabolome profile in adolescent males with KS is distinctly different from that in males without KS independent of age, obesity, pubertal development, or testosterone treatment status and is suggestive of differences in mitochondrial β-oxidation.

Mitochondria are a dynamic eukaryotic innovation that play diverse roles in biology and disease. The mitochondrial genome is remarkably conserved in all vertebrates, encoding the same 37-gene set and overall genomic structure, ranging from 16,596 base pairs (bp) in the teleost zebrafish (Danio rerio) to 16,569 bp in humans. Mitochondrial disorders are amongst the most prevalent inherited diseases, affecting roughly 1 in every 5000 individuals. Currently, few effective treatments exist for those with mitochondrial ailments, representing a major unmet patient need. Mitochondrial dysfunction is also a common component of a wide variety of other human illnesses, ranging from neurodegenerative disorders such as Huntington’s disease and Parkinson’s disease to autoimmune illnesses such as multiple sclerosis and rheumatoid arthritis. The electron transport chain (ETC) component of mitochondria is critical for mitochondrial biology and defects can lead to many mitochondrial disease symptoms. Here, we present a publicly available collection of genetic mutants created in highly conserved, nuclear-encoded mitochondrial genes in Danio rerio. The zebrafish system represents a potentially powerful new opportunity for the study of mitochondrial biology and disease due to the large number of orthologous genes shared with humans and the many advanced features of this model system, from genetics to imaging. This collection includes 15 mutant lines in 13 different genes created through locus-specific gene editing to induce frameshift or splice acceptor mutations, leading to predicted protein truncation during translation. Additionally, included are 11 lines created by the random insertion of the gene-breaking transposon (GBT) protein trap cassette. All these targeted mutant alleles truncate conserved domains of genes critical to the proper function of the ETC or genes that have been implicated in human mitochondrial disease. This collection is designed to accelerate the use of zebrafish to study many different aspects of mitochondrial function to widen our understanding of their role in biology and human disease.

10581 Background: MSI-H colorectal cancer is most often a result of deleterious mutations in mismatch repair genes, but can also occur through repressed gene transcription due to hypermethylation of the MLH1 promoter, often associated with BRAF V600E mutations. However, there is a subset of patients who have a “constitutional epimutation”, resulting in hypermethylation of MLH1 throughout normal tissue. We observed a young patient develop a second primary Lynch associated malignancy (see Table 1) who was found to have a constitutional epimutation in MLH1 that prompted us to review the frequency with which the test was ordered and the positivity rate, as well as outline the clinical history in the positive cases. Methods: We reviewed all of the testing ordered for MLH1 hypermethylation of peripheral blood (MLHPB) at the Mayo Clinic Laboratory between 09/01/2020 and 09/01/2021. To the best of our knowledge, this is the only clinically available testing lab in the United States. We reviewed positive casesfor characteristics including the number of malignancies, age of diagnosis, and family history. Results: 33 MLHPB total tests were ordered in the United States at the Mayo Clinic laboratories between 09/01/2020 and 09/01/2021. Three of the tests were positive, including the single test ordered by our institution, and one of the two additional positive tests was available for detailed review. Our institution’s positive test case was a 41 year old women who developed T4N2M0 colorectal cancer 5 years after being treated for endometrial cancer. She had endometrial cancer with absence of MLH1 and PMS2 staining and had a negative germline cancer risk panel at age 36. Five years later, she developed a T4N2 colorectal cancer after which repeat germline testing with RNA sequencing was negative and she was found to have constitutional MLH1 promoter hypermethylation. We were able to obtain clinical information about two of the three individuals with positive tests (See Table). Conclusions: Recognition of constitutional MLH1 hypermethylation may allow for earlier recognition of Lynch related malignancies in affected patients and families. Testing appears infrequent and this condition often goes unrecognized. Specific consensus guidelines may improve recognition and cancer screening in this population. [Table: see text]

One key bottleneck in understanding the human genome is the relative under-characterization of 90% of protein coding regions. We report a collection of 1200 transgenic zebrafish strains made with the gene-break transposon (GBT) protein trap to simultaneously report and reversibly knockdown the tagged genes. Protein trap-associated mRFP expression shows previously undocumented expression of 35% and 90% of cloned genes at 2 and 4 days post-fertilization, respectively. Further, investigated alleles regularly show 99% gene-specific mRNA knockdown. Homozygous GBT animals in ryr1b , fras1 , tnnt2a , edar and hmcn1 phenocopied established mutants. 204 cloned lines trapped diverse proteins, including 64 orthologs of human disease-associated genes with 40 as potential new disease models. Severely reduced skeletal muscle Ca 2+ transients in GBT ryr1b homozygous animals validated the ability to explore molecular mechanisms of genetic diseases. This GBT system facilitates novel functional genome annotation towards understanding cellular and molecular underpinnings of vertebrate biology and human disease.

When vertebrates face acute stressors, their bodies rapidly undergo a repertoire of physiological and behavioral adaptations, which is termed the stress response. Rapid changes in heart rate and blood glucose levels occur via the interaction of glucocorticoids and their cognate receptors following hypothalamic‐pituitary‐adrenal axis activation. These physiological changes are observed within minutes of encountering a stressor and the rapid time domain rules out genomic responses that require gene expression changes. Although behavioral changes corresponding to physiological changes are commonly observed, it is not clearly understood to what extent hypothalamic‐pituitary‐adrenal axis activation dictates adaptive behavior. We hypothesized that rapid locomotor response to acute stressors in zebrafish requires hypothalamic‐pituitary‐interrenal (HPI) axis activation. In teleost fish, interrenal cells are functionally homologous to the adrenocortical layer. We derived eight frameshift mutants in genes involved in HPI axis function: two mutants in exon 2 ofmc2r(adrenocorticotropic hormone receptor), five in exon 2 or 5 ofnr3c1(glucocorticoid receptor [GR]) and two in exon 2 ofnr3c2(mineralocorticoid receptor [MR]). Exposing larval zebrafish to mild environmental stressors, acute changes in salinity or light illumination, results in a rapid locomotor response. We show that this locomotor response requires a functioning HPI axis via the action ofmc2rand the canonical GR encoded bynr3c1gene, but not MR (nr3c2). Our rapid behavioral assay paradigm based on HPI axis biology can be used to screen for genetic and environmental modifiers of the hypothalamic‐pituitary‐adrenal axis and to investigate the effects of corticosteroids and their cognate receptor interactions on behavior.