#3599 ADTKD diagnosis: an evolving challenge

BACKGROUND AND AIMS ADTKD represents a recently described group of kidney diseases, characterized by chronic interstitial nephritis (CIN), in most cases hereditary, with an autosomal dominant inheritance pattern, subclassified according to its genetic cause, when identified. Mutations in UMOD, MUC1, REN and HNF1B genes have been implicated in their pathogenesis. Recent molecular diagnostic technologies, such as next-generation sequencing (NGS), and particularly the use of restriction and snapshot method for the detection of a cytosine insertion on the coding variable-number tandem repeat (VNTR) sequence in the MUC1 gene encoding mucin 1, have allowed the nephrologists to diagnose renal diseases of previously unknown cause, with a real prevalence probably underestimated. We present the cohort of patients identified with ADTKD in the nephrogenetics clinic from the nephrology department of our hospital from 2015 to 2021. METHOD patients with CKD of unknown etiology and renal phenotype suggesting chronic interstitial nephritis (bland urine analysis, hyperuricemia and/or anemia unrelated to the degree of chronic kidney disease, hypo/hypercalemia, acidemia, urinary concentration defects, absent hypertension and renal cysts), especially with a family history of similar CKD, were referred for the nephrogenetics clinic and ADTKD was investigated. In these cases, we performed a genetic study of ADTKD by the following steps: (1) UMOD, REN, HNF1 B mutations studied through next-generation sequencing (NGS); (2) if negative, search for the insertion of a single cytosine of the repeat unit comprising the extremely long (∼1.5–5 kb), GC-rich (>80%) coding VNTR sequence in the MUC1 gene encoding mucin 1 (see Kirby et al. 2013). It is used a restriction and snapshot method. (3) If negative, search for HNF1B Large deletion, detected by multiplex ligation-dependent probe amplification (MLPA) (kit P241-D2, MRC-Holland). Pre-genetic counseling was performed by the nephrologist and post-genetic counseling was performed by the nephrologist and geneticist, namely to proceed with family screening of potentially affected family members when a pathogenic mutation was identified or when segregation studies were necessary. RESULTS A total of 30 families were studied and a confirmed genetic diagnosis was obtained in 10 (30%), allowing the identification of 29 patients with ADTKD; the mutations identified were in MUC1 in four families (13 patients), UMOD in four families (11 patients), HNF 1 beta (1 family, 4 patients) and REN: one patient with a phenotype compatible with ADTKD but with a genotype compatible with renal tubular dysgenesis (two mutations in REN gene from each of the parents). Three families are still under study: two families are being studied with segregation studies to evaluate the pathogenicity of mutations in UMOD (1 family) and HNF1B (1 family), and one family with a phenotype of ADTKD (three young patients with positive family history) with negative results for mutations in ADTKD genes is in study, pursuing with WES. If positive results are obtained for these three families, the percentage of families identified through the use of this protocol will increase to 43.3% of the families studied through this model. CONCLUSION In our cohort, a genetic diagnosis was established in 30% of the families studied. MUC 1 and UMOD are the most prevalent genes implicated in ADTKD at our center, similar to what has been reported in other cohorts of ADTKD. Given the rarity of these diseases and the fact that they require specific molecular techniques for accurate diagnosis, we believe that nephrogenetics clinics with dedicated nephrologists and geneticists in straight cooperation are critical for accurate diagnosis.

Phenotypic Heterogeneity of ADTKD-MUC1 Diagnosed Using VNtyper, a Novel Genetic Technique.

The MUC1 gene is associated with autosomal dominant tubulointerstitial kidney disease (ADTKD), leading to CKD. Current methods of sequencing, like exome sequencing, rarely detect MUC1 pathogenic variants because of the variable number of tandem repeats (VNTR) in MUC1 exon2. We demonstrated that combining fast read filtering with a sensitive VNTR genotyping strategy enables systematic screening of 27dupC pathogenic MUC1 variant from exome data. We initially validated our bioinformatics pipeline in a proof-of-concept cohort incorporating exome data from 33 participants with a known MUC1 pathogenic variant identified by Snapshot PCR and confirmed by 54 MUC1-negative individuals for negative control. We then retrospectively analyzed exome sequencing data from January 2019 to October 2023 from 3512 adult participants with nephropathy of unknown origin. Finally, we prospectively validated our pipeline in 825 additional participants enrolled from November 2023. SharkVNTyper accurately identified MUC1 variants in 32 out of 33 participants and excluded its presence in all the 54 negative controls in the proof-of-concept cohort (sensitivity of 97%, specificity of 100%). Integration of Shark tool with VNTyper significantly reduced running time from 6-12 hours to 5-10 minutes per sample, allowing both retrospective and prospective analysis. In the retrospective cohort, SharkVNTyper identified 23 additional positive cases that were not suspected clinically and had been missed in the initial exome analysis; 18 of these cases were confirmed as carrying the MUC1 27dupC mutation by low-throughput Snapshot PCR. In the prospective cohort of 825 CKD cases, systematic screening discovered 13 positive cases, with 12 confirmed by PCR. Overall, of 63 participants (1.4% of 4653) with molecularly confirmed ADTKD-MUC1, comprehensive diagnoses and descriptions of the disease were available for 24 participants. Median age of kidney failure was 50 years, 38% exhibited bilateral multiple kidney cysts, 8% had early-onset gout, and 58% had arterial hypertension. SharkVNTyper enables the analysis of highly repeated regions, such as the MUC1 VNTR, and facilitates the systematic screening of ADTKD-MUC1 from exome data, fostering 27dupC variation identification.

P3-09-05: Clinical outcome of patients with advanced triple negative breast cancer with germline and somatic variants in homologous recombination gene

ACMG SF v3.0 list for reporting of secondary findings in clinical exome and genome sequencing: a policy statement of the American College of Medical Genetics and Genomics (ACMG)

Autosomal dominant tubulointerstitial kidney disease (ADTKD) constitutes a spectrum of rare, but underdiagnosed renal disorders. ADTKD presents with a bland urinary sediment (no hematuria and little to no proteinuria), usually has no extrarenal manifestations (with the exception of HNF1B- associated disease), and results in a slowly progressive chronic kidney disease. Renal failure typically occurs in the fourth to fifth decade of life. Despite a uniform clinical picture, there is substantial interfamilial- and intrafamilial diversity in progression of CKD sometimes ranging from before the third to beyond the sixth decade of life. ADTKD shows modest genetic heterogeneity, with four main types ( UMOD , MUC1 , HNF1B , and REN ) accounting for the vast majority of cases. However, sometimes ADTKD is used as an umbrella term for a broader number of isolated or syndromal conditions that may present with an ADTKD phenotype. The two most common ADTKD types caused by pathogenic variants in the glycoproteins uromodulin ( UMOD ), mucin 1 ( MUC1 ), and the enzyme renin ( REN ) show striking similarities in their molecular pathophysiology and are considered toxic proteinopathies. From a spectrum of kidney disease virtually unknown to the public and to large parts of the medical community before the identification of UMOD as the first identified cause of ADTKD (then termed MCKD2) in 2002, ADTKD is increasingly recognized as a leading genetic cause of kidney disease in adults. The identification of MUC1 as the cause for the second main type has greatly stimulated research on all aspects of ADTKD and unveiled important molecular insights into its underlying pathophsiology. Our molecular knowledge on common ADTKD forms has passed the critical threshold required for developing targeted therapeutic strategies and personalized treatment approaches can be expected in the near future.

Background and Aims The European patient organization for Autosomal Dominant Tubulointerstitial Kidney Disease (ADTKD) raises awareness and funds cure research (www.adTKD.de/en-gb). At least five disease genes (UMOD, MUC1, REN, HNF1B, and SEC61A1) have causative mutations, with more expected [1]. Due to its non-specific clinical presentation, only a genetic test can diagnose it. The variable number tandem repeat (VNTR) region in ADTKD-MUC1, the second most common subtype, makes detection difficult. Therefore, many patients are misdiagnosed or undiagnosed [2]. Due to the Broad Institute in the US and the University of Erlangen in Germany testing potentially effective ADTKD compounds, this unsatisfactory diagnostic situation is growing [4]. Moreover, a European initiative is registering ADTKD patients in the ERKNet database, paving the way for clinical drug trials. We aim to highlight the complexity of ADTKD-MUC1 genetic testing and examine recently published diagnostic solutions that could make testing more common in clinical practice. Method We conducted a comprehensive review of the latest literature on ADTKD-MUC1, focusing on the challenges of the VNTR region and evaluating existing and newly developed testing strategies. We compared these methods based on feasibility, accuracy, cost, invasiveness, and usability in clinical laboratories. Results The gold standard for MUC1 gene testing, SNaPShot, targets the VNTR region (up to 130 repeats of 60 base pairs with high GC content) but is only offered by a small number of European laboratories. This method is labor-intensive and does not reveal the exact location of the pathogenic variant. In countries such as Germany, reimbursement remains problematic, further limiting its routine use [2]. Our survey revealed that some European countries (e.g., the Netherlands, Ireland, and the United Kingdom) still lack in-country options for MUC1 genetic testing, making cross-border collaborations essential [2]. Recent advances allow detection of MUC1 variants in short-read next-generation sequencing (NGS) data, but the VNTR region's repetitive and GC-rich nature complicates straightforward bioinformatic analysis. Newly developed approaches, such as VNtyper [3], provide alignment-free genotyping from NGS data, detecting whether a pathogenic insertion is present (Fig. 2). VNtyper has now been updated to version 2.0, featuring improved variant-calling algorithms, a more user-friendly pipeline, and a web server (vntyper.org) offering free, online access. Version 2.0 can integrate additional modules for improved filtering (SHARK) and alternative genotyping (code-adVNTR), expanding its utility for various sequencing setups. Immunohistochemistry can identify mutated MUC1 in kidney tissue, confirming ADTKD-MUC1 status non-genetically. This method requires a kidney biopsy and does not pinpoint the mutation's location. Long-read sequencing platforms (e.g., Oxford Nanopore and PacBio) can overcome the limitations of short-read methods by avoiding reliance on PCR amplification in the repetitive VNTR region. Although still under development for clinical application, they have the potential to pinpoint the exact location of the MUC1 variant. Conclusion The diagnostic complexity of ADTKD-MUC1 arises primarily from the VNTR region's repetitive, GC-rich structure. Although SNaPShot remains the diagnostic gold standard, new NGS-based methods, such as the updated VNtyper 2.0 pipeline, will allow for broad screening, while long-read sequencing approaches will provide promising alternatives for more detailed diagnostics. With clinical trials for new ADTKD treatments looming [4], improving and standardizing MUC1 testing is critical. The widespread adoption of accessible, reliable genetic testing methods in Europe and beyond will be critical for identifying patients early, guiding therapeutic interventions, and accelerating drug development for ADTKD-MUC1.

Background and Aims Recent advances in genetic molecular techniques have allowed the expansion of knowledge in glomerular diseases of genetic cause, including the identification of genes involved in focal and segmental glomerular sclerosis (FSGS). The prevalence of adult-onset genetic FSGS varies widely depending on the population studied. In central Europe, NPHS2 and COL4A3, COL4A4 e COL4A5 genes are postulated to be the most frequent genes implicated in genetic causes of adult FSGS. This study aims to characterize patients submitted to genetic study of glomerular diseases in the Nephrogenetics Clinic of our centre. Method We conducted a single-centre retrospective analysis of the patients submitted to genetic study of glomerular diseases in the Nephrogenetics Clinic of our centre from 2016 to 2022. Adult patients with a glomerular disease phenotype suggestive of a genetic cause were studied, using a predetermined phenotype-targeted panel of genes, through massive parallel sequencing. The number of genes included in this panel has increased (from 21 genes in 2016 to 49 genes since 2018); given this change, patients with a negative result on the first approach repeated screening with the broader panel. Additionally, patients presenting with advanced chronic kidney disease (CKD) without an identifiable phenotype, studied with a larger panel for CKD causing genes, are reported. In patients with a negative result but highly suggestive presentation, whole exome sequencing (WES) was considered, after multidisciplinary discussion with a Geneticist's evaluation. Patients with variants of unknown significance (VUS) were referred to a Genetics’ consultation for genetic counselling and segregation studies. Results Of the 80 patients studied (comprising 74 families), 52.5% were female (n=42) and 79% (n=63) of Caucasian ascent. Mean age was 45.4 ± 16.0 years. Nine patients were studied with the larger gene panel for CKD. 85% (n=68) had CKD (all stages) at presentation, with proteinuria (ranging from sub-nephrotic to nephrotic range) and 15% had asymptomatic urinary changes. 50% (n=40) of patients had positive family history, and 31% (n=25) had a syndromic presentation and/or extra renal manifestations. 27.5% (n=22) had a renal biopsy, and the most prevalent result was FSGS (11%; n=9). Genetic variants were identified in 70% (n=56) of the patients; but pathogenicity is not fully established in all: genotype-phenotype correlations, including inheritance pattern and histological correlation, and segregation studies (when indicated and possible) are ongoing. In 5 patients results are pending. Pathogenic / likely pathogenic variants were identified in at least 47.5% (n=38) patients. The most frequently implicated genes were: COL4A3, COL4A4 e COL4A5 (n=21), high risk APOL1 (n=8); NPSH2 (n=5), IFN2 (n=6, 3 pathogenic, 1 variant of unknown significance (VUS), 2 under segregation studies) and MYH9 (n=3). COL4A3, COL4A4 e COL4A5 mutations occur with Alport syndrome, but also with histologically documented FSGS, sub-nephrotic and nephrotic proteinuria, nephrotic syndrome and asymptomatic urinary changes. In our cohort, NPHS2 p.R229Q was identified in 5 patients (6%), but only with pathogenic significance in 3 patients, and APOL1 high risk haplotype was co-identified with COL4 variants in 3 patients. Conclusion The genetic study of a cohort of patients suspected of genetic FSGS allowed the identification of genetic variants in the genes of interest in a high percentage of cases. The most frequently implicated genes were COL4A3, COL4A4 e COL4A5, NPHS2, INF2 and APOL1 high risk haplotype. The high percentage of gene variants identified in our cohort is probably due to the selection of a population with a high likelihood of genetic FSGS. Further studies will clarify the causal and/or modifier effect of some genes, namely COL4A3, COL4A4 e COL4A5. The future use of WES in cases of high likelihood of genetic cause will probably allow the identification on novel candidate genes and increase the clinical benefits of a genetic diagnosis of FSGS.

Genetic renal disorders and genomic screening of renal disease

Dear Editors, Dowling-Degos disease(DDD) (OMIM # 615327) is a benign genodermatosis classified as a reticular pigmented dermatosis.1 Lesions typically appear in adulthood between the second and fifth decades, on intertriginous regions, acral areas, genital areas, and the extremities, presenting as symmetric and progressive macular reticular hyperpigmentation with reddish-brown papules and plaques.1, 2 The pathogenesis is linked to variants in specific genes, including Protein O-fucosyltransferase 1-POFUT1 (OMIM* 607491).1 Here, we report a novel likely pathogenic variant in the POFUT1 gene identified in a family with DDD, supported by clinical, histopathological, and genetic findings. A 51-year-old healthy Turkish woman presented with asymptomatic bilateral pigmented lesions in the axillary and inguinal regions, which had developed since her twenties. Dermatological examination revealed reticular hyperpigmented macules and patches on her face, neck, axillae, inframammary folds, inguinal and genital regions, arms, dorsal hands, and pits on bilateral palms (Figure 1a–c). Seborrheic keratosis (SK) appeared on her neck and shoulder in her forties. Histopathological analysis of a hyperpigmented lesion showed elongation of the rete ridges, focal increased pigmentation at the tips of the rete. Based on the clinical and histopathological findings, a diagnosis of DDD was considered. With informed consent, genomic DNA was extracted from her peripheral blood. Whole exome sequencing (Qiagen, Germany), identified a novel heterozygous likely pathogenic POFUT1 variant, NM_015352.2(POFUT1):c.1047dup (p.Phe350LeufsTer34), (PVS1, PM2) in exon 7 that causes a frameshift, leading to a truncated and likely nonfunctional POFUT1 protein, which is related to DDD. The index patient's mother, an 81-year-old woman, developed similar reticular hyperpigmented lesions on her neck, axillae, inframammary folds, inguinal and genital regions, arms, dorsum of the feet consistent with DDD since her twenties and multiple SKs later on her forties (Figure 1d–f). The index patient's 24-year-old son did not have any lesions. With informed consent, genetic testing was conducted for the index patient's father, mother, brother, and son. Sanger sequencing was performed to confirm the presence of the variant in the patient and to assess its segregation among available family members, her son and her mother were heterozygous for NM_015352.2(POFUT1):c.1047dup variant (Figure 2b). Similar lesions were reported in eleven relatives; however, no material was available for genetic testing or segregation analysis (Figure 2a). At the 1-year follow-up of the index case, newly developed hyperpigmented lesions were noted in the perianal region. In addition, both the patient and her mother showed an increase and further darkening of hyperpigmented lesions. The genetic causes of DDD involve variants in multiple genes. Five casual pathogenic variants in keratin 5 (KRT5), POGLUT1, POFUT1, PSENEN, and GLMN have been identified in association with the disease.1-4 In 2013, Li et al. discovered variants in the POFUT1 gene in patients with DDD.1, 3 Functional analysis indicates that POFUT1 plays a role in melanin synthesis, transport and regulation of keratinocyte proliferation and differentiation.1, 3 The novel heterozygous NM_015352.2(POFUT1):c.1047dup variant identified in our patients has not been previously reported in major genetic databases (NCBI, dbSNP, HGMD, ClinVar). Based on ACMG/AMP 2015 guidelines and available data, it has been classified as likely pathogenic, supported by PVS1 (predicted loss-of-function through a frameshift in a gene where haploinsufficiency is a known disease mechanism) and PM2 (absence from large population databases).5 This frameshift variant introduces a premature stop codon, truncating the protein and disrupting its function. Its occurrence in multiple affected family members further supports its pathogenic role. Literature indicates a range of clinical findings in DDD patients linked to various gene variants.1, 3, 4 A recent review by Kumar et al4 expanded the clinical spectrum of DDD, highlighting at least five distinct subphenotypes associated with specific genetic variants. Of particular relevance, POFUT1-associated DDD (subphenotype II) is characterized by acral and genital hyperpigmentation in addition to classical flexural involvement. In line with this evolving definition, index patient and her mother exhibited genital involvement, further supporting the concept that DDD extends beyond flexural sites. However, her son had no lesions associated with DDD, suggesting variability in the onset of clinical manifestations within the same family despite identical variants. In literature POFUT1 variants in DDD are also reported to be linked to distinct clinical manifestations, including multiple SKs, and psoriasis.1, 6 Our patients had multiple SKs. A reported case with a deletion in the POFUT1 gene showed DDD lesions appearing in the fifth decade, multiple SKs appearing in childhood.6 In our cases, DDD lesions appeared in the third decade followed by SKs in the fifth with a duplication in the POFUT1 gene. The identification of the novel pathogenic variant NM_015352.2:c.1047dup (p.Phe350LeufsTer34) expands current knowledge of POFUT1-related pathogenic variants. Further reports may be helpful in elucidating the relationship between genotype and phenotype in DDD. None.

Genetic counseling in direct-to-consumer exome sequencing: a case report.

Background and Aims Cystinuria (CU) is an inherited renal disorder based on urinary wasting of dibasic amino acids, urinary precipitation, and consecutive cystine stone formation. It is caused by pathogenic variants in two distinct disease genes, SLC3A1 and SLC7A9, both of which encode subunits of a heterodimeric tubular amino acid transporter, rBAT/SLC3A1 and BAT1/SLC7A9, located at the apical membrane of proximal renal tubules. CU is marked by incomplete penetrance and substantial disease variability. Recently, a novel cystine transporter, consisting of the light chain AGT1/SLC7A13 and its heterodimeric partner rBAT/SLC3A1 has been identified in the S3 segment of murine proximal tubules. In this study, we aim at evaluating the role of AGT1 in cystinuric patients with or without mutations in either SLC3A1 or SLC7A9, analyzing the role of AGT1/SLC7A13 as novel disease gene or genetic modifier in CU. Method A multicenter European CU-cohort comprising 132 individuals was screened for pathogenic variants in SLC3A1, SLC7A9, and SLC7A13 using high-throughput multiplex PCR-based amplification and next-generation sequencing (MiSeq Illumina) followed by multiplex ligation-dependent probe amplification (MLPA) of SLC3A1 and SLC7A9. For functional in vitro studies, epitope-tagged human and murine rBAT and AGT1 proteins were transiently expressed in different cell systems. Heterodimer complex formation was analyzed by co-immunoprecipitation and western blot studies and membrane trafficking was evaluated by immunofluorescence microscopy. Results Genectic analysis of our CU-cohort did not reveal indiviuals with SLC7A13 variation only, however we found three patients harbouring heterozygous missense variants in addition to pathogenic or VUS variants in SLC3A1 or SLC7A9. To evaluate their influence on the generation of functional cystine transporters in vitro, different cell models were transiently transfected with plasmids expressing wildtype or mutant proteins. In line with previous reports, co-expression of AGT1 and rBAT wildtype allowed efficient complex formation as AGT1-induced maturation of rBAT was detected by increased mature N-glycosylation, co-immunoprecipitation and membrane insertion. Whereas AGT1 patient variants p.Met452Thr (SLC7A13 c.1355T>C) and p.Ile174Phe (SLC7A13 c.520A>T) behaved comparable to wildtype AGT1, variants p.Asn45Lys (SLC7A13 c.135C>G) and p.Leu270Phe (SLC7A13 c.808C>T) led to clearly reduced glycosylation patterns and trafficking deficits of rBAT wildtype protein. Next, the mutual influence of pathogenic variation in both, AGT1 and rBAT, will unravel the consequences of patient-specific molecular interactions on the functional expression of cystine transporter complexes. Conclusion Here, we report three CU-patients with variants in SLC7A13 combined with either SLC3A1 or SLC7A9. For two of these variants, in vitro functional analysis revealed pathogenic molecular mechanisms disturbing complex formation, maturation and trafficking of rBAT. We hypothesize that specific pathogenic variants in SLC7A13 interfere with efficient membrane localization of heterodimeric cystine transporters, which results in modulation of cystine transport in the S3 segment of proximal tubules in CU-patients.

BackgroundAt present, Multiplex ligation-dependent probe amplification (MLPA) and exome sequencing are common gene detection methods in patients with Duchenne muscular dystrophy or Becker muscular dystrophy (DMD/BMD), but they can not cover the whole-genome sequence of the DMD gene. In this study, the whole genome capture of the DMD gene and next-generation sequencing (NGS) technology were used to detect the patients with DMD/BMD in Southwest China, to clarify the application value of this technology and further study the gene variant spectrum.MethodsFrom 2017 to 2020, 51 unrelated patients with DMD/BMD in southwestern China were clinically diagnosed at West China Second University Hospital of Sichuan University (Chengdu, China). The whole-genome of the DMD gene was captured from the peripheral blood of all patients, and next-generation sequencing was performed. Large copy number variants (CNVs) in the exon regions of the DMD gene were verified through MLPA, and small variations (such as single nucleotide variation and < 50 bp fragment insertions/deletions) were validated using Sanger sequencing.ResultsAmong the 51 patients, 49 (96.1% [49/51]) had pathogenic or likely pathogenic variants in the DMD gene. Among the 49 positive samples, 17 patients (34.7% [17/49]) had CNVs in the exon regions and 32 patients (65.3% [32/49]) had small variations. A total of six novel variants were identified: c.10916_10917del, c.1790T>A, c.1842del, c.5015del, c.5791_5792insCA, and exons 38–50 duplication.ConclusionsPathogenic or likely pathogenic variants of the DMD gene were detected in 49 patients (96.1% [49/51]), of which 6 variants (12.2% [6/49]) had not been previously reported. This study confirmed the value of NGS-based targeted sequencing for the DMD gene expanding the spectrum of variants in DMD, which may provide effective genetic counseling and prenatal diagnosis for families.

In children and adolescents, osteosarcoma (OS) is the most common malignant bone tumor. OS occurs in certain cancer predisposition syndromes at a higher than expected frequency. However, outside of these rare syndromes, OS is significantly more common and its genetic etiology remains poorly understood. We conducted an evaluation of rare exonic variants in 545 unselected OS cases compared with 1061 cancer-free controls using whole-exome sequencing of blood or buccal cell DNA to estimate the prevalence and burden of rare deleterious germline variants. We assessed potentially pathogenic rare variants in 126 established cancer predisposing genes (CPG) and known somatically mutated genes. We also surveyed the exome for genes with a higher burden of rare variants in 342 EUR cases with 994 EUR controls sequenced at the same time. Rare genetic variants, defined by a MAF &amp;lt;0.01 in 1000G, ESP or ExAC, that passed quality control filters were classified based on well-annotated databases (IARC-TP53, Telomerase Database, ARUP, BIC, Insight and COSMIC-hotspots), variant databases (e.g. Clinvar, HGMD and LOVD), and in silico predictions (Sift, Polyphen, Mutation assessor, MutationTaster, FATHMM and LTR). Rare variants matching known pathogenic variants, or inexact matches at the same residue, in selected well-annotated databases were labeled as putative pathogenic variants. High impact variants (frameshift, stop gain/loss, or known splice sites) not matching a previously identified pathogenic variant in the selected databases were categorized as probably pathogenic. Predictions based solely on in silico predictions were categorized as possibly pathogenic, uncertain or likely benign. A total of 14.5% of cases had a predicted pathogenic or high impact variant in an autosomal dominant CPG. A significantly higher pathogenic rare variant burden was present in EUR cases compared with EUR controls (Pburden=3.7x10-05). TP53 had the highest prevalence of pathogenic mutations (5% of EUR cases; Pburden=1.05x10-09). CDKN2A, MEN1, MLH1, MUTYH, PALB2 and VHL had a significantly higher rare variant burden in the EUR cases. 7.5% of cases had a predicted pathogenic or probably pathogenic variant in an autosomal recessive CPG (Pburden=5.4x10-03). Additionally, two males had a pathogenic variant in the X-linked genes, DKC1 and GPC3. In total, 21% of cases had a predicted pathogenic or high impact variant in a CPG (Pburden=2.4x10-07). Exome-wide analysis identified two novel genes with significantly higher rare variant burdens in the cases compared to controls. In conclusion, several CPGs and two novel genes, not previously associated with OS, had an enrichment of rare variants in OS and warrant further follow-up. Our results indicate that a clinically significant fraction of OS cases may harbor one or more mutations worthy of consideration for further investigation and genetic counseling. Citation Format: Roelof Koster, Bin Zhu, Meredith Yeager, Michael Dean, Matthew Gianferante, Lei Song, Joshua Sampson, NCI DCEG Cancer Genomics Research Laboratory, Julie Gastier-Foster, Richard Gorlick, Silvia Regina Caminada de Toledo, Antonio Petrilli, Ana Patiño-Garcia, Fernando Lecanda, Massimo Serra, Claudia Hattinger, Piero Picci, Katia Scotlandi, Adrienne Flanagan, Roberto Tirabosco, Maria Amary, Nilgün Kurucu, Inci Ergurhan Ilhan, Neriman Sari, Mandy Ballinger, David Thomas, Donald Barkauskas, Belynda Hicks, Margaret Tucker, Neil Caporaso, Robert Hoover, Stephen Chanock, Sharon Savage, Lisa Mirabello. Whole-exome sequencing identifies a high frequency of germline deleterious variants in cancer predisposition genes in individuals with osteosarcoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4871. doi:10.1158/1538-7445.AM2017-4871

Autosomal Dominant Tubulointerstitial Kidney Disease: Clinical Presentation of Patients With ADTKD-UMOD and ADTKD-MUC1