Unraveling the intrafamilial correlations and heritability of tumor types in MEN1: a Groupe d'étude des Tumeurs Endocrines study

BACKGROUND

MEN1, which is secondary to the mutation of the MEN1 gene, is a rare autosomal-dominant disease that predisposes mutation carriers to endocrine tumors. Most studies demonstrated the absence of direct genotype-phenotype correlations. The existence of a higher risk of death in the Groupe d'étude des Tumeurs Endocrines-cohort associated with a mutation in the JunD interacting domain suggests heterogeneity across families in disease expressivity. This study aims to assess the existence of modifying genetic factors by estimating the intrafamilial correlations and heritability of the six main tumor types in MEN1.

METHODS

The study included 797 patients from 265 kindred and studied seven phenotypic criteria: parathyroid and pancreatic neuroendocrine tumors (NETs) and pituitary, adrenal, bronchial, and thymic (thNET) tumors and the presence of metastasis. Intrafamilial correlations and heritability estimates were calculated from family tree data using specific validated statistical analysis software.

RESULTS

Intrafamilial correlations were significant and decreased along parental degrees distance for pituitary, adrenal and thNETs. The heritability of these three tumor types was consistently strong and significant with 64% (s.e.m.=0.13; P<0.001) for pituitary tumor, 65% (s.e.m.=0.21; P<0.001) for adrenal tumors, and 97% (s.e.m.=0.41; P=0.006) for thNETs.

CONCLUSION

The present study shows the existence of modifying genetic factors for thymus, adrenal, and pituitary MEN1 tumor types. The identification of at-risk subgroups of individuals within cohorts is the first step toward personalization of care. Next generation sequencing on this subset of tumors will help identify the molecular basis of MEN1 variable genetic expressivity.

Uveal melanoma hepatic metastases mutation spectrum analysis using targeted next-generation sequencing of 400 cancer genes

AIMS

Uveal melanoma (UM) is the most common malignant tumour of the eye. Diagnosis often occurs late in the course of disease, and prognosis is generally poor. Recently, recurrent somatic mutations were described, unravelling additional specific altered pathways in UM. Targeted next-generation sequencing (NGS) can now be applied to an accurate and fast identification of somatic mutations in cancer. The aim of the present study was to characterise the mutation pattern of five UM hepatic metastases with well-defined clinical and pathological features.

METHODS

We analysed the UM mutation spectrum using targeted NGS on 409 cancer genes.

RESULTS

Four previous reported genes were found to be recurrently mutated. All tumours presented mutually exclusive GNA11 or GNAQ missense mutations. BAP1 loss-of-function mutations were found in three UMs. SF3B1 missense mutations were found in the two UMs with no BAP1 mutations. We then searched for additional mutation targets. We identified the Arg505Cys mutation in the tumour suppressor FBXW7. The same mutation was previously described in different cancer types, and FBXW7 was recently reported to be mutated in UM exomes.

CONCLUSIONS

Further studies are required to confirm FBXW7 implication in UM tumorigenesis. Elucidating the molecular mechanisms underlying UM tumorigenesis holds the promise for novel and effective targeted UM therapies.

SPRED1, a RAS MAPK pathway inhibitor that causes Legius syndrome, is a tumour suppressor downregulated in paediatric acute myeloblastic leukaemia

Constitutional dominant loss-of-function mutations in the SPRED1 gene cause a rare phenotype referred as neurofibromatosis type 1 (NF1)-like syndrome or Legius syndrome, consisted of multiple café-au-lait macules, axillary freckling, learning disabilities and macrocephaly. SPRED1 is a negative regulator of the RAS MAPK pathway and can interact with neurofibromin, the NF1 gene product. Individuals with NF1 have a higher risk of haematological malignancies. SPRED1 is highly expressed in haematopoietic cells and negatively regulates haematopoiesis. SPRED1 seemed to be a good candidate for leukaemia predisposition or transformation. We performed SPRED1 mutation screening and expression status in 230 paediatric lymphoblastic and acute myeloblastic leukaemias (AMLs). We found a loss-of-function frameshift SPRED1 mutation in a patient with Legius syndrome. In this patient, the leukaemia blasts karyotype showed a SPRED1 loss of heterozygosity, confirming SPRED1 as a tumour suppressor. Our observation confirmed that acute leukaemias are rare complications of the Legius syndrome. Moreover, SPRED1 was significantly decreased at RNA and protein levels in the majority of AMLs at diagnosis compared with normal or paired complete remission bone marrows. SPRED1 decreased expression correlated with genetic features of AML. Our study reveals a new mechanism which contributes to deregulate RAS MAPK pathway in the vast majority of paediatric AMLs.