What is a Rare Genetic Disorder of Obesity?

A genetic disorder is any condition that is caused when a gene has a variant that prevents it from working the way it should.

Recently, genetic variants have been identified along the melanocortin-4 (MC4) genetic pathway, which is responsible for regulating weight and appetite. These variants, although very rare, can lead to disorders that cause severe obesity. This type of disorder is known as a rare genetic disorder of obesity and is responsible for a very small percentage of all obesity cases.

Rare genetic disorders of obesity are different from a genetic predisposition to obesity. When someone has a genetic predisposition to obesity, they have genetic factors which contribute to the development of obesity but do not directly cause it. Rare genetic disorders of obesity, on the other hand, are directly caused by specific variants in one’s genetic makeup.

There are several different rare genetic disorders of obesity, but those caused by variants in the MC4 pathway have a few things in common. First, people with rare genetic disorders of obesity will often have severe obesity that begins early in life, sometimes even in infancy. This is known as early-onset obesity. And secondly, they will experience a feeling of intense, unrelenting hunger called hyperphagia.

The Genetic Obesity Project is focusing on 5 of these rare genetic disorders of obesity.

  • Proopiomelanocortin (POMC) Deficiency Obesity

    POMC deficiency obesity is a rare genetic disorder characterized by severe obesity and hyperphagia beginning at an early age and persisting throughout life.

    People with POMC are more likely to have red hair and very light skin, although this is not always the case. They may also have low levels of adrenocorticotropic hormone (ACTH), which may lead to a condition called adrenal insufficiency that can cause low blood sugar levels (hypoglycemia), seizures, and other problems in the body.

  • Leptin Receptor (LEPR) Deficiency Obesity

    Like POMC, LEPR deficiency obesity is a rare genetic disorder that leads to severe obesity and hyperphagia beginning at an early age and persisting throughout life. People with LEPR deficiency obesity may grow at a normal rate during childhood but reach a shorter adult height.

    People with LEPR deficiency obesity also have hypogonadotropic hypogonadism, which is caused by low hormone levels in the body that can result in delayed puberty, underdeveloped sex glands (testicles or ovaries), and infertility.

  • Bardet-Biedl Syndrome (BBS)

    Bardet-Biedl syndrome (BBS) is a rare genetic disorder that is caused by more than one genetic variant. Each person with BBS will experience different symptoms, but most become obese beginning early in life.

    One of the most visible symptoms of BBS is having extra fingers or toes (polydactyly) at birth. They may also have learning or speech difficulties and hypogonadism, a condition in which the sex glands do not produce enough hormones.

    People with BBS often experience vision loss and may become legally blind. In addition, they may develop type 2 diabetes, high blood pressure, very high cholesterol levels, and kidney disease.

  • Alström Syndrome

    Alström syndrome is a rare genetic disorder that affects many parts of the body. While the symptoms may begin in childhood, sometimes they do not appear until later in life. People with Alström syndrome can experience obesity and serious medical problems in the liver, kidney, bladder, and lungs.

    Often, Alström syndrome leads to type 2 diabetes, hearing and vision loss, a type of heart disease called dilated cardiomyopathy, and reduced height.

  • Prader-Willi Syndrome

    Prader-Willi syndrome has many effects on the body, including behavior, development, and obesity, which can be life-threatening. People with Prader-Willi syndrome experience hyperphagia and slowed metabolism, which can lead to severe obesity. In addition, they may have weak muscle tone, known as hypotonia, poor growth, and delayed development in childhood.

    People with Prader-Willi syndrome often have intellectual impairment, learning disabilities, and behavioral problems, as well.

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Not all obesity is the same. We've spent years studying rare genetic disorders of obesity, but there's more to learn.

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The Genetic Obesity Project is dedicated to helping people better understand certain genetic causes that result in conditions known as rare genetic disorders of obesity. Watch the video to see why getting a diagnosis is an important step.

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The Genetic Obesity Project is an initiative of Rhythm Pharmaceuticals, Inc. The content on this site is intended for use by patients, caregivers, and healthcare professionals for informational purposes only and is not intended to be taken as medical advice.
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