Unraveling the Genetic Architecture of Hepatoblastoma Risk: Birth Defects and Increased Burden of Germline Damaging Variants in Gastrointestinal/Renal Cancer Predisposition and DNA Repair Genes

The ultrarare hepatoblastoma (HB) is the most common pediatric liver cancer. HB risk is related to a few rare syndromes, and the molecular bases remain elusive for most cases. We investigated the burden of rare damaging germline variants in 30 Brazilian patients with HB and the presence of additional clinical signs. A high frequency of prematurity (20%) and birth defects (37%), especially craniofacial (17%, including craniosynostosis) and kidney (7%) anomalies, was observed. Putative pathogenic or likely pathogenic monoallelic germline variants mapped to 10 cancer predisposition genes (CPGs: APC, CHEK2, DROSHA, ERCC5, FAH, MSH2, MUTYH, RPS19, TGFBR2 and VHL) were detected in 33% of the patients, only 40% of them with a family history of cancer. These findings showed a predominance of CPGs with a known link to gastrointestinal/colorectal and renal cancer risk. A remarkable feature was an enrichment of rare damaging variants affecting different classes of DNA repair genes, particularly those known as Fanconi anemia genes. Moreover, several potentially deleterious variants mapped to genes impacting liver functions were disclosed. To our knowledge, this is the largest assessment of rare germline variants in HB patients to date, contributing to elucidate the genetic architecture of HB risk.

Abstract 2072: Genomic studies of Brazilian patients with hepatoblastoma: Insight into somatic mutations using whole-exome sequencing

Hepatoblastomas (HB) are embryonal tumors of the liver with histological features that resemble different stages of liver differentiation. The identification of molecular pathways involved in HB development can expand the understanding of the connections between disruption of normal differentiation and cancer. Exome sequencing (244K Agilent SureSelect Target Enrichment) analysis was performed for 6 HBs matched with their non tumoral liver tissues (fresh frozen tissues). Bioinformatic analysis of exome data identified somatic variants in 69 genes which were chosen for validation using a target sequencing panel (SureSelectXT Target Enrichment System for Illumina Paired-End Sequencing Library). The gene panel was composed of the detected 69 genes and other 48 genes related with HB or cancer, and it was used to investigated additional 13 HB samples as a validation group. 60% of the patients were male, and the mean age at diagnosis was 36 months. 13% of this cohort presented pulmonary metastasis. All patients received pre-surgery chemotherapy (SIOPEL and COG protocol).

Results: A total of 71 somatic rare coding mutations (missense and loss-of-function) were validated in 53 genes considering the entire HB group. The somatic analysis reveals pathogenic mutations in the CTNNB1 gene and a recurrent missense mutation in the CX3CL1 gene; the role of these mutations was explored by IHQ studies of their proteins as well as by gene expression analysis by RT-PCR. We also used results from Illumina 450k to evaluated the methylation levels of CX3CL1 and CX3CR1 genes. Methylation values for CpG sites in each sample were measured as β-and CpG sites were grouped into categories, promoter (1stExon; 5'UTR; TSS1500; TSS200) or gene body, information provided by Illumina, based on UCSC data (GRhC 37). The methylation level of each category was obtained by averaging the β-values of all CpGs mapped in the category for each gene, followed by Wilcoxon test correction by calculating the false discovery rate (FDR).

Conclusion: Most investigated HBs carry few potentially pathogenic genetic mutations (≤ 5 mutations). This observed low frequency of somatic mutations is a result similar to previous studies. The proposed explanation is based on the fact that pediatric tumors would originate from precursor cells with pluripotent characteristics; therefore, such tumors may require fewer mutations than adult solid tumors to develop. The congenital HB case of our cohort is discrepant from this scenario since a relatively high number of somatic mutations were found compared to the HB group. To our knowledge, this is the first comprehensive genomic characterization of Brazilian HBs. Next steps include expanding the casuistry of exome sequenced tumors, including two cases of HB associated with Hirschprung disease.

Grants: FAPESP (2016/04785-0; 2017/11212-0), FAPESP (2013/08028-1), CNPq (141625/2016-3).

Citation Format: Talita F. Aguiar, Tatiane Rodrigues, Maria Prates, Fernanda Aparecida dos Santos, Gustavo Fernandes, Cecília Maria Lima da Costa, Isabela Werneck da Cunha, Monica Cypriano, Silvia Regina Caminada de Toledo, Jorge Estefano S. de Souza, Eugênia Valadares, Raquel Borges, Vicente Odone, Israel Tojal, Dirce Carraro, Carla Rosenberg, Ana C.V. Krepischi. Genomic studies of Brazilian patients with hepatoblastoma: Insight into somatic mutations using whole-exome sequencing [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2072.

Mucopolysaccharidosis I, II, and VI: Brief review and guidelines for treatment

Mucopolysaccharidoses (MPS) are rare genetic diseases caused by the deficiency of one of the lysosomal enzymes involved in the glycosaminoglycan (GAG) breakdown pathway. This metabolic block leads to the accumulation of GAG in various organs and tissues of the affected patients, resulting in a multisystemic clinical picture, sometimes including cognitive impairment. Until the beginning of the XXI century, treatment was mainly supportive. Bone marrow transplantation improved the natural course of the disease in some types of MPS, but the morbidity and mortality restricted its use to selected cases. The identification of the genes involved, the new molecular biology tools and the availability of animal models made it possible to develop specific enzyme replacement therapies (ERT) for these diseases. At present, a great number of Brazilian medical centers from all regions of the country have experience with ERT for MPS I, II, and VI, acquired not only through patient treatment but also in clinical trials. Taking the three types of MPS together, over 200 patients have been treated with ERT in our country. This document summarizes the experience of the professionals involved, along with the data available in the international literature, bringing together and harmonizing the information available on the management of these severe and progressive diseases, thus disclosing new prospects for Brazilian patients affected by these conditions.

A clinical study of 77 patients with mucopolysaccharidosis type II

AIM

This study aims to assess the clinical features of 77 South American patients (73 Brazilian) with mucopolysaccharidosis type II (MPS II).

METHODS

Details of the patients and their disease manifestations were obtained from a review of medical records, interviews with the patients and/or their families, and physical examination of the patients.

RESULTS

Mean birth weight was 3360 g, median age at onset of symptoms was 18 months and median age at diagnosis was 6 years. For the whole sample (median age, 8.2 years; range, 2.8-53.0 years), neurological degeneration, typical pebbly skin lesions, seizures and extensive dermal melanocytosis were found in 23.3, 13.0, 13.0 and 1.3% of the cases, respectively. The most frequently reported echocardiogram abnormality was mitral valve regurgitation. Refraction errors were the most common ophthalmological manifestation. The following characteristics were found to be associated with the severe form of MPS II: earlier age at biochemical diagnosis, higher levels of urinary glycosaminoglycans, language development delay, behavioural disturbances, poor school performance and mental retardation.

CONCLUSION

Our results suggest that there is a considerable delay between the onset of signs and symptoms and the diagnosis of MPS II in Brazil (and probably in South America as well), and that many complications of this disease are underdiagnosed and undertreated. Therefore, the implementation of programmes aiming to increase the awareness of the disease, the availability of biochemical diagnostic tests and the provision of better support to affected patients is urgently needed.

Clinical and biochemical study of 28 patients with mucopolysaccharidosis type VI

This paper presents data collected by a Brazilian center in a multinational multicenter observational study of patients with mucopolysaccharidosis type VI (MPS VI), aiming at determining the epidemiological, clinical, and biochemical profile of these patients. Twenty-eight south-American patients with MPS VI were evaluated through medical interview, physical exam, echocardiogram, electrocardiogram, ophthalmologic evaluation, quantification of glycosaminoglycans (GAGs) in urine, and measurement of the activity of N-acetylgalactosamine-4-sulfatase (ARSB) in leukocytes. 92.9% of patients were Brazilian. Mean age at diagnosis and at evaluation was 48.4 months and 97.1 months, respectively. 88% of patients had onset of symptomatology before the age of 36 months. Consanguinity was reported by 27% of the families. Mean weight and height at birth were 3.481 kg and 51.3 cm, respectively. The most frequently reported clinical manifestations were short stature, corneal clouding, coarse facial features, joint contractures, and claw hands. All patients presented with echocardiogram changes as well as corneal clouding. Mean ARSB activity in leukocytes was 5.4 nmoles/h/mg protein (reference values: 72-174), and urinary excretion of GAGs was on average 7.9 times higher than normal. The number of clinical manifestations did not show a significant correlation with the levels of urinary GAGs nor with the ARSB activity. Also, no significant correlation was found between the levels of urinary GAGs and the ARSB activity. It was concluded that MPS VI has high morbidity and that, when compared with data published in the literature, patients in our study were diagnosed later and presented with a higher frequency of cardiological findings.