Mutations in Two Genes, USP48 and BRAF, Linked to Cushing’s Disease

Mutations in USP48 and BRAF genes contribute to the overproduction of adrenocorticotropin (ACTH) hormone by the pituitary gland and consequent development of Cushing’s disease, a study shows, linking these genes to the disease for a first time.

The study, “Identification of recurrent USP48 and BRAF mutations in Cushing’s disease,” published in the journal Nature Communications, also identified a possible treatment for patients with BRAF-related mutations.

Cushing’s disease is a condition characterized by excessive cortisol levels that, if left untreated, can lead to serious cardiovascular problems, infections, and mood disorders. It usually arises from benign pituitary tumors that produce too much of ACTH hormone, which in turn stimulates the adrenal glands to secrete cortisol.

It is still not clear why some people develop these tumors, but studies have pointed to mutations in the USP8 gene as a possible cause. They are present in 35%–62% of all tumor cases, and influence treatment response and long-term outcomes.

But major disease drivers in people whose tumors have no evidence of  USP8 mutations are unknown. Recognizing this gap, researchers in China examined tumor tissue samples from 22 patients with pituitary ademonas but a normal USP8 gene.

Their analysis revealed four genes that were recurrently mutated, including two — BRAF and USP48 — never before reported in this disease setting. Then, looking at 91 samples from patients, researchers found BRAF mutations in 17% of cases and USP48 mutations in 23% of patients.

These mutations were also found in patients with USP8-mutant pituitary tumors, but at a much lower rate — 5.1% for BRAF and 1.2% for USP48 mutations.

However, mutations in these two genes were not seen in patients with pituitary tumors producing other hormones, suggesting they are “unique genetic signatures of [ACTH-producing] adenomas,” the researchers wrote.

The team also found that BRAF and USP48 mutations activate signaling pathways that lead to the production of proopiomelanocortin (POMC), which is the precursor of ACTH.

“ACTH overproduction is a hallmark of Cushing’s disease and appears to be frequently induced by mutations in genes that tightly regulate POMC gene transcription in the pathogenesis of this disease,” investigators wrote.

Patients with BRAF and USP48 mutations had significantly higher levels of midnight plasma ACTH and midnight serum cortisol, compared to patients without these mutations. Tumor size, however, was similar among the two groups.

Interestingly, the team found that the BRAF inhibitor Zelboraf (vemurafenib) effectively reduced ACTH production in cells from ACTH-producing pituitary tumors. Zelboraf, marketed by Genentech, is approved in the U.S. and Europe to treat cancers with BRAF mutations, and findings suggest it may be a good therapeutic candidate for some people with Cushing’s disease.

“The mutational status of BRAFUSP8, and USP48 in corticotroph adenomas may be used in the future to characterize the molecular subtypes and guide targeted molecular therapy,” the researchers suggested.

From https://cushingsdiseasenews.com/2018/11/20/mutations-in-usp48-braf-genes-contribute-for-cushings-disease-study-finds/

The Pituitary Gland: Small But Mighty

The pituitary gland works hard to keep you healthy, doing everything from ensuring proper bone and muscle growth to helping nursing mothers produce milk for their babies. Its functionality is even more remarkable when you consider the gland is the size of a pea.

“The pituitary is commonly referred to as the ‘master’ gland because it does so many important jobs in the body,” says Karen Frankwich, MD, a board-certified endocrinologist at Mission Hospital. “Not only does the pituitary make its own hormones, but it also triggers hormone production in other glands. The pituitary is aided in its job by the hypothalamus. This part of the brain is situated above the pituitary, and sends messages to the gland on when to release or stimulate production of necessary hormones.”

These hormones include:

  • Growth hormone, for healthy bone and muscle mass
  • Thyroid-stimulating hormone, which signals the thyroid to produce its hormones that govern metabolism and the body’s nervous system, among others
  • Follicle-stimulating and luteinizing hormones for healthy reproductive systems (including ovarian egg development in women and sperm formation in men, as well as estrogen and testosterone production)
  • Prolactin, for breast milk production in nursing mothers
  • Adrenocorticotropin (ACTH), which prompts the adrenal glands to produce the stress hormone cortisol. The proper amount of cortisol helps the body adapt to stressful situations by affecting the immune and nervous systems, blood sugar levels, blood pressure and metabolism.
  • Antidiuretic (ADH), which helps the kidneys control urine levels
  • Oxytocin, which can stimulate labor in pregnant women

The work of the pituitary gland can be affected by non-cancerous tumors called adenomas. “These tumors can affect hormone production, so you have too little or too much of a certain hormone,” Dr. Frankwich says. “Larger tumors that are more than 1 centimeter, called macroadenomas, can also put pressure on the area surrounding the gland, which can lead to vision problems and headaches. Because symptoms can vary depending on the hormone that is affected by a tumor, or sometimes there are no symptoms, adenomas can be difficult to pinpoint. General symptoms can include nausea, weight loss or gain, sluggishness or weakness, and changes in menstruation for women and sex drive for men.”

If there’s a suspected tumor, a doctor will usually run tests on a patient’s blood and urine, and possibly order a brain-imaging scan. An endocrinologist can help guide a patient on the best course of treatment, which could consist of surgery, medication, radiation therapy or careful monitoring of the tumor if it hasn’t caused major disruption.

“The pituitary gland is integral to a healthy, well-functioning body in so many ways,” Dr. Frankwich says. “It may not be a major organ you think about much, but it’s important to know how it works, and how it touches on so many aspects of your health.”

Learn more about Mission Hospital. Learn more about Dr. Frankwich.

From http://www.stjhs.org/HealthCalling/2016/December/The-Pituitary-Gland-Small-but-Mighty.aspx

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