DOT1L Gene Variants Linked to Emerging Neurological Disorder

So far, only partial loss-of-function DOT1L variants in around half of KMT-encoding genes (16 of 34) have been shown to cause dominant human developmental disorders. “We found the variants in DOT1L cause a dominant disorder through a gain-of-function mechanism, which is different from other KMTs,” said Dr. Bellen.

Although DOT1L is involved in several fundamental cellular processes, and its misregulation has been implicated in cancer, prior to this study it was not clear how variants in the DOT1L gene cause a congenital disorder. So, Dr. Zelha Nil, the first author and postdoctoral associate in the Bellen lab, turned to fruit flies to address that question.

DOT1L and its fruit fly version, grappa (gpp) have similar protein sequences and are also likely to have overlapping functions. Most disease-causing human variants in DOT1L are located in its enzymatic domain. Furthermore, gpp is expressed in a large subset of neurons and some glial cells. The team generated a fly gpp mutant, which grew slowly and died in larval stages. Using these mutant flies and flies in which gpp RNA was knocked down, they found compelling evidence that gpp is essential for the survival of the flies and required for proper development as well as the development and function of the fly nervous system, and for H3K79 methylation.

“We attempted to suppress the lethality of gpp mutant flies by expressing the human DOT1L gene in flies,” Dr. Zelha Nil said. “To our surprise, expressing normal or variant versions of the human DOT1L gene in tissues where it occurs naturally in flies was not sufficient for gpp mutants who had lost both copies of the gene to survive. Surprisingly, flies with a partial loss of gpp that expressed the human DOT1L variants were less viable and had more profound morphological defects than the normal DOT1L expressing flies, suggesting the human DOT1L expression in flies was toxic.” Consistent with this observation, gpp mutant flies and cultured cells expressing variant versions of human DOT1L exhibited significantly higher levels of H3K79 methylation than normal DOT1L, suggesting that elevated levels of methylation are the likely molecular cause of the symptoms seen in the patients.

“Based on our studies in flies, it appears that the variants result in excess enzymatic activity of DOT1Lin these patients,” Dr. Bellen said. “While additional studies are needed to unravel the exact mechanism of disease pathogenesis, our study suggests that reducing DOT1L activity is a viable therapeutic strategy that can be developed in the future to treat this new genetic condition.”

Source: Eurekalert