Scientists at The Feinstein Institutes for Medical Research, in collaboration with Columbia University, say they have identified a gene mutation that could result in schizophrenia, a chronic brain disorder that affects nearly one percent of the world’s population. Their study “Novel ultra-rare exonic variants identified in a founder population implicate cadherins in schizophrenia,” published in Neuron, could lead to novel treatment strategies, according to the team.

“The identification of rare variants associated with schizophrenia has proven challenging due to genetic heterogeneity, which is reduced in founder populations. In samples from the Ashkenazi Jewish population, we report that schizophrenia cases had a greater frequency of novel missense or loss of function (MisLoF) ultra-rare variants (URVs) compared to controls, and the MisLoF URV burden was inversely correlated with polygenic risk scores in cases,” write the investigators.

“Characterizing 141 ‘case-only’ genes (MisLoF URVs in ≥3 cases with none in controls), the cadherin gene set was associated with schizophrenia. We report a recurrent case mutation in PCDHA3 that results in the formation of cytoplasmic aggregates and failure to engage in homophilic interactions on the plasma membrane in cultured cells. Modeling purifying selection, we demonstrate that deleterious URVs are greatly overrepresented in the Ashkenazi population, yielding enhanced power for association studies. Identification of the cadherin/protocadherin family as risk genes helps specify the synaptic abnormalities central to schizophrenia.”

The research team, led by Todd Lencz, PhD, with Itsik Pe’er, PhD, Tom Maniatis, PhD, and Erin Flaherty, PhD, of Columbia University, carried out a genetic study identifying a single letter change in the DNA code in the PCDHA3 gene that is associated with schizophrenia. The affected gene makes a type of protein called a protocadherin, which generates a cell surface “barcode” required for neurons to recognize, and communicate with, other neurons. They found that the PCDHA3 variant blocks this normal protocadherin function.

The discovery was made possible by the special genetic characteristics of the samples studied by Lencz’s team—patients with schizophrenia and healthy volunteers drawn from the Ashkenazi Jewish population. The Ashkenazi Jewish population represents an important population for study based on its unique history. Just a few hundred individuals who migrated to Eastern Europe less than 1,000 years ago are the ancestors of nearly 10 million Ashkenazi Jews today. This lineage, combined with a tradition of marriage within the community, has resulted in a more uniform genetic background in which to identify disease-related variants.

“In addition to our primary findings regarding PCDHA3 and related genes, we were able— due to the unique characteristics of the Ashkenazi population—to replicate several prior findings in schizophrenia despite relatively small sample sizes,” said Lencz, professor in the Institute of Behavioral Science at the Feinstein Institutes. “In our study, we demonstrated this population represents a smart, cost-effective strategy for identifying disease-related genes. Our findings allow us to zero in on a novel aspect of brain development and function in our quest to develop new treatments for schizophrenia.”

“Lencz’s research into the role of genetics in schizophrenia offers a major advance,” said Kevin J. Tracy, MD, president and CEO of the Feinstein Institutes. “This work may open new avenues to developing therapeutics, which are sorely needed.”

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