Analysis of mutations in EXT1 and EXT2 in Brazilian patients with multiple osteochondromas.

BACKGROUND: Multiple osteochondromas is a dysplasia characterized by growth of two or more osteochondromas. It is genetically heterogeneous, caused by pathogenic variants in EXT1 or EXT2 genes in 70%-90% of patients. The EXT1 is more often mutated than EXT2 gene, with a variable prevalence between populations. There are no data about EXT1 and EXT2 pathogenic variants in patients with multiple osteochondromas in Brazilian population. The aim of this survey is to characterize these to determine the genotype profile of this population. METHODS: DNA sequencing (Sanger Method) and MLPA analysis were performed to identify point mutations and deletions/duplications in the sample of 153 patients in 114 families. RESULTS: Germline variants were identified in 83% of families in which EXT2 variants were detected in 46% and EXT1 in 37% of cases. No variants were detected in 17% of them. We identified 50 different variants, 33 (13 frameshift, 11 nonsense, 5 missense, 2 splice site mutation, and 2 large deletions) in EXT1 and 17 (6 frameshift, 6 splice site mutation, 3 nonsense, 1 missense, and 1 large deletion) in EXT2. Of all 50 variants, 31 (62%) were novel, including 20 out of 33 (60,6%) EXT1 and 11 out of 17 (64.7%) EXT2 alleles. The vast majority of variants (88%) were "loss-of-function" and two novel hotspots in EXT2 gene were observed in our study. CONCLUSION: The prevalence of variants detected in the EXT2 gene differs from other researches from Latin America, European, and Asian population. This uncommon prevalence could be related with the newly characterized variant hotspot sites detected in EXT2 gene (p.Ala409Profs*26 and p.Ser290*). A high number of novel variants were also identified indicating that Brazilian population has a unique genetic profile. Characterizing this population and establishing its genotype is essential to understand the molecular pathogenesis of this disease in Brazil.

SF-1 overexpression in childhood adrenocortical tumours.

The steroidogenic factor 1 (SF-1) gene encodes a transcription factor playing a pivotal role in the regulation of adrenogenital development. We have recently shown that SF-1 is amplified in childhood adrenocortical tumours (ACT). This study was aimed to assess if an increase in SF-1 gene copy number was associated with increased protein levels and to study the correlation between SF-1 expression and ACT clinical parameters. An increased SF-1 copy number was detected in eight of the 10 ACT cases studied. Conversely, the SF-1 protein was found to be overexpressed in all cases, compared to normal age-matched adrenal glands. No significant correlation was found between SF-1 protein levels and its gene copy number. Furthermore, no significant correlation existed with histological grade or with the clinical manifestation or evolution of disease. This data show that SF-1 overexpression is widespread in childhood ACT and is likely to play a role in its pathogenesis.