March 2 (UPI) -- Researchers at Massachusetts General Hospital found the gene variant that causes red hair and increases the risk of melanoma, may be the cause of the link between melanoma and Parkinson's disease.
There is a known association between melanoma and Parkinson's disease. Patients with Parkinson's disease have an increased risk for melanoma, and patients diagnosed with melanoma are at increased risk of developing Parkinson's disease.
In the study, mice carrying the red hair variant of the melanocortin 1 receptor, or MC1R, gene were found to have reduced production of the neurotransmitter dopamine in the substantia nigra, the part of the brain where dopamine-producing neurons are destroyed in patients with Parkinson's disease.
Inherited MC1R gene variants are responsible for skin pigmentation. The most common form leads to greater production of eumelanin, a darker pigment. The red-hair-associated variant inactivates the gene's function and increases production of the lighter pigment pheomelanin.
Pheomelanin offers less protection from ultraviolet radiation than eumelanin, and may contribute to the development of melanoma, researchers said.
"This study is the first to show direct influences of the melanoma-linked MC1R gene on dopaminergic neurons in the brain and may provide evidence for targeting MC1R as a novel therapeutic strategy for PD [Parkinson's disease]," Dr. Xiqun Chen, a researcher at the MassGeneral Institute for Neurodegenerative Disease at Massachusetts General Hospital, said in a press release.
"It also forms a foundation for further interdisciplinary investigators into the dual role of this gene in tumorigenesis within melanocytes -- the pigment cells in which melanoma develops -- and the degeneration of dopaminergic neurons, improving our understanding of why and how melanoma and Parkinson's disease are linked."
Results showed mice with most common form of the MC1R gene express it in dopamine-producing neurons in the substantia nigra. Red-haired mice with the gene inactivated due to mutation had fewer dopamine-producing neurons, which became fewer as the mice aged, along with a progressive decline in movement.
The mice were more sensitive to toxic substances that damage dopamine-producing neurons and increased oxidative stress, which is a known association with melanoma risk.
The study was published in the Annals of Neurology.