Researchers at the National Institutes of Health have discovered a new genetic disorder characterized by developmental delays and malformations of the brain, heart and facial features. Named linkage-specific-deubiquitylation-deficiency-induced embryonic defects syndrome (LINKED), it is caused by a mutated version of the OTUD5 gene, which interferes with key molecular actions in embryo development.

The findings indicate that the newly identified pathway may be essential for human growth and may also underlie other disorders that are present at birth. The information will help scientists better understand such diseasesboth common and rareand enhance patient care. The results were reported Jan. 20, 2021 at Science Advances.

The project began when David B. Beck, M.D., Ph.D., a clinical fellow in the laboratory of Dan Kastner M.D., Ph.D., at the National Human Genome Research Institute (NHGRI) and co-first author, was asked to consult on a male baby who had been born with severe birth defects that included abnormalities of the brain, craniofacial skeleton, heart and urinary tract.

Our discovery of the dysregulated neurodevelopmental pathway that underlies LINKED syndrome was only possible through the teamwork of geneticists, developmental biologists and biochemists from NIH,. This collaboration provided the opportunity to pinpoint the likely genetic cause of disease, and then take it a step further to precisely define the sequence of cellular events that are disrupted to cause the disease.

Achim Werner, Ph.D., Investigator, National Institute of Dental and Craniofacial Research (NIDCR) and Lead Author

An in-depth examination of siblings and family members genomes, combined with hereditary bioinformatics analyses, revealed a mutation in the OTUD5 gene as the possible cause of the problem. Through outreach to other researchers working on similar problems, Beck found seven additional males ranging from 1 to 14 years of age who shared symptoms with the first patient and had varying mutations in the OTUD5 gene.

The gene comprises instructions for making the OTUD5 enzyme, which is involved in ubiquitylation, a process which molecularly alters a protein to change its purpose. Ubiquitylation plays a part in governing cell fate, where stem cells are taught to turn into specific cell types in the early stages of embryo development.

According to the genetic evidence, I was pretty sure OTUD5 mutations caused the disease, but I did not understand how this enzyme, when mutated, led to the symptoms seen in our patients, said Beck. For this reason we sought to work with Dr. Werners group, which specializes in using biochemistry to comprehend the functions of enzymes such as OTUD5.

To begin, the NIH team analyzed cells taken from patient samples, which were processed in the NIH Clinical Center. Usually, OTUD5 edits or eliminates molecular tags on particular proteins (substrates) to modulate their function. However, in cells from patients with OTUD5 mutations, this activity was diminished.

Using a method to reunite mature human cells into the stem cell-like state of embryo cells, the scientists discovered that OTUD5 mutations were linked to abnormalities in the development of neural crest cells, which give rise to tissues of the craniofacial skeleton, and of neural precursors, cells that eventually give rise to the brain and spinal cord.

In additional experiments, the team discovered that the OTUD5 enzyme acts on a few protein substrates called chromatin remodelers. This class of proteins alters the closely packed strands of DNA in a cells nucleus to make sure genes accessible for being turned on, or expressed.

With help from collaborators led by Pedro Rocha Ph.D., an investigator in the National Institute of Child Health and Human Development (NICHD), the group found that chromatin remodelers targeted by OTUD5 help enhance expression of genes that control the cell fate of neural precursors during embryo development.

Taken together, the investigators reasoned, OTUD5 normally keeps these chromatin remodelers from being tagged for destruction. However, while OTUD5 is mutated, its protective function is lost and the chromatin remodelers are destroyed, leading to abnormal development of neural precursors and neural crest cells. Ultimately, these changes can lead to some of the birth defects seen in LINKED patients.

This implies that the mechanism we discovered is a portion of a common developmental pathway that, when mutated at different points, will result in a spectrum of disease.

We were amazed to discover that OTUD5 elicits its effects via multiple, functionally related substrates, which shows a new principle of cellular signaling during early embryonic development, said Mohammed A. Basar, Ph.D., a postdoctoral fellow in Werners lab and co-first author of this study. These findings lead us to believe that OTUD5 may have far-reaching effects beyond those identified in LINKED patients.

In future work, Werners team plans to fully investigate the role which OTUD5 and similar enzymes play in development. The researchers hope the study can serve as a guiding framework for unraveling the causes of other undiagnosed diseases, ultimately helping clinicians better evaluate and care for patients.

Were finally able to provide families with a diagnosis, bringing an end to what is often a long and exhausting search for answers, said Beck.

Source:

Journal reference:

Beck, D.B.,et al.(2021) Linkage-specific deubiquitylation by OTUD5 defines an embryonic pathway intolerant to genomic variation.Science Advances.doi.org/10.1126/sciadv.abe2116.

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