A recurrent de novo splice site variant involving DNM1 exon 10a causes developmental and epileptic encephalopathy through a dominant-negative mechanism.

Heterozygous pathogenic variants in DNM1 cause developmental and epileptic encephalopathy (DEE) as a result of a dominant-negative mechanism impeding vesicular fission. Thus far, pathogenic variants in DNM1 have been studied with a canonical transcript that includes the alternatively spliced exon 10b. However, after performing RNA sequencing in 39 pediatric brain samples, we find the primary transcript expressed in the brain includes the downstream exon 10a instead. Using this information, we evaluated genotype-phenotype correlations of variants affecting exon 10a and identified a cohort of eleven previously unreported individuals. Eight individuals harbor a recurrent de novo splice site variant, c.1197-8G>A (GenBank: NM_001288739.1), which affects exon 10a and leads to DEE consistent with the classical DNM1 phenotype. We find this splice site variant leads to disease through an unexpected dominant-negative mechanism. Functional testing reveals an in-frame upstream splice acceptor causing insertion of two amino acids predicted to impair oligomerization-dependent activity. This is supported by neuropathological samples showing accumulation of enlarged synaptic vesicles adherent to the plasma membrane consistent with impaired vesicular fission. Two additional individuals with missense variants affecting exon 10a, p.Arg399Trp and p.Gly401Asp, had a similar DEE phenotype. In contrast, one individual with a missense variant affecting exon 10b, p.Pro405Leu, which is less expressed in the brain, had a correspondingly less severe presentation. Thus, we implicate variants affecting exon 10a as causing the severe DEE typically associated with DNM1-related disorders. We highlight the importance of considering relevant isoforms for disease-causing variants as well as the possibility of splice site variants acting through a dominant-negative mechanism.

Cancer genetic counseling for childhood cancer predisposition is associated with improved levels of knowledge and high satisfaction in parents.

Previous surveys of adults with cancer have revealed increased levels of genetic knowledge, varying levels of worry, and high satisfaction with cancer genetic counseling. We sought to determine the impact of cancer genetic counseling on parental levels of genetic knowledge, worry about cancer, and satisfaction in the context of suspected cancer predisposition in a child. We hypothesized that parents would be satisfied with cancer genetic counseling and that cancer genetic counseling would improve baseline parental genetic knowledge and decrease levels of worry. Parents were recruited from a pediatric cancer predisposition clinic in the United States. A survey was administered to two cohorts: One cohort had received cancer genetic counseling in the past and only completed one survey (post-only, n = 26), and another cohort completed the survey before and after cancer genetic counseling (pre/post, n = 23). The survey included questions on demographics, knowledge of genetics, worry levels, and satisfaction with the cancer genetic counseling service. The post-genetic counseling survey also contained a free-text section for parents to indicate what they took away from the sessions. Parental levels of genetics knowledge increased by an average of 1.9 points (p = .01), with 65.2% of parents demonstrating an increase in genetics knowledge score. Average worry levels did not change significantly (p = .37), with 52.2% of parents indicating decreased worry, and 34.8% indicating increased worry. Overall, 91.8% of parents reported high levels of satisfaction. Our results show that cancer genetic counseling in a pediatric cancer predisposition clinic improves parental levels of genetics knowledge. Satisfaction rates suggest that parents find this service beneficial. These results demonstrate the positive impacts of cancer genetic counseling on parents of children in which a hereditary cancer syndrome is known or suspected.