When sequencing does not identify a rare disease

Routine sequencing has given an unprecedented insight into the genetics of rare diseases, but genomics does not diagnose up to half of the patients tested. This is the problem that German scientists have tackled in a recent review of the journal Molecular and cellular proteomics. Using patient samples from four countries and a new neutrophil proteome database, they were able to make a genetic diagnosis for two children with severe conbad neutropenia whose sequencing had failed.

"There are very few examples of people who use multiple" methods "to investigate rare diseases … (but) I think that's the future of personalized medicine," he says. said senior author Christoph Klein, physician and director of the Child & # 39; s Medicine Hospital of Munich University.

Patients' disease affects their neutrophils, white blood cells filled with toxic proteins to deploy against bacteria. If the development of neutrophils is disrupted, according to Klein, it happens to one newborn out of 200,000, each bacterial or fungal infection can become a medical emergency that can lead to death.

Neutrophils are fragile, making them difficult to study. Postdoctoral researcher Sebastian Hesse has developed a protocol for collecting healthy neutrophil proteins. Scientists led by Piotr Grabowski of Juri Rappsilber's proteomics lab at Berlin Technical University then used these healthy cells to establish a basic neutrophil proteome.

Next, Hesse collected neutrophils from 16 patients with conbad neutropenia. Some of them lived in Germany; to reach others, he had to travel to Turkey and Iran. Mbad spectrometers repeated the same proteomic test to compare neutrophils from patients to volunteers.

The team used abnormal protein profiles to diagnose two patients whose exome sequencing results were inconclusive. In the case of a child, a pseudogene has made it difficult to identify mutations in the gene encoding the protein; in the second case, incomplete coverage by exome sequencing had missed a key mutation. Protein abundance data in each patient led the researchers to perform secondary genetic badyzes that were found to be successful.

Both mutations are known causes of neutropenia. "It shows that even if you have highly controlled pipelines for genetic studies, you still risk not being 100% correct," said Klein. In a future article, the team will report on new genetic causes of neutropenia discovered through the proteogenomic technique.

Proteomic and genomic combined screening is not yet practical for all patients. "But, if you look at the machines that are being developed, I think there will be tremendous potential for proteome badysis at a very low cost," Klein said.

Provided by
American Society of Biochemistry and Molecular Biology