What is MVID?

WHAT IS MVID?

An intestinal, pediatric disease

Microvillus inclusion disease (MVID) is a rare, genetic disorder caused by a mutation in the MYO5B gene that limits the growth and function of cells in the intestine. As a result, these immature cells cannot absorb fluids, nutrients, or electrolytes.

Infants with MVID develop persistent and severe diarrhea within hours, days, or months after birth. This prevents them from getting the necessary nutrition – resulting in malnutrition, stunted growth, and in most cases, a significantly shortened lifespan.

Other names for the disease include:

» Congenital microvillus atrophy

» Davidson’s Disease

» Familial protracted diarrhea

Treatment of MVID

MVID patients are dependent on intravenous (IV) fluid, known as total parenteral nutrition (TPN) to receive nutrition and hydration. Consequently, the MVID intestine has often been considered by doctors and clinicians to be a failed organ, and it is often advocated that patients receive an intestinal transplant early in the course of the disease. However, new research suggests that the immature cells of the MVID intestine have the potential to mature and function (therefore, allowing the body to absorb the necessary nutrition and hydration) with proper treatment.

Healthy Intestine vs. MVID Intestine

The inside of a healthy intestine is lined with a single layer of fingerlike cells, called villi. The surface of these cells is lined with thousands of tiny brushlike structures, called microvilli.

The microvilli layer has three main responsibilities:

DIGESTION

Breaking down food

ABSORPTION

Taking water, salts, and nutrients from the intestine into the body

SECRETION

The opposite of absorption: sending fluid and mucus into the intestine

Intestinal cell development and maturation

Intestinal cells are born in the crevices between neighboring villi (called intestinal glands, or crypts). With time, they progress further and further away from the depth of the crypts. As the cells climb up the villus, they mature and change function from secretion to absorption, and eventually die at the tip of the villus. The whole process takes around 72 hours.

Healthy Intestine

As cells migrate upwards, they acquire mature features when they surface from the depth of intestinal crypts.

Mature cells (red) cover the villi. Well-equipped for absorption, they are responsible for taking water, nutrients, and electrolytes into the body.

Immature cells (green) – predominantly secrete, sending fluid and mucus into the intestine.

MVID Intestine

The maturation process is impaired in the diseased intestine, resulting in the overall immature state of the intestinal cells. As a result, the villi are shortened, and the cells are not equipped for absorption.

Immature cells (green) – immature MVID cells perform secretion, continuously producing fluids into the opening of the intestine and worsening diarrhea.

Absorption and secretion imbalance

In the healthy intestine, absorption and secretion are balanced. After a healthy infant drinks or eats, the intestine transfers nutrients, water, and electrolytes to the rest of the body, while secreting or releasing just enough fluid to help waste move through the digestive system.

However, the intestine of an MVID patient is out of balance. It severely and continuously secretes much more than it absorbs because cells and ion channels, which would normally drain or absorb fluid from the gut, do not form. Instead, the cells are frozen in an immature state, where their main task is to secrete fluids into the intestine. This causes the intestine to overflow, resulting in serious diarrhea. Critical nutrients, water, and electrolytes are not absorbed into the body when the infant eats or drinks; and are instead lost in the stool. Because of this imbalance, an infant with MVID can lose up to one third of his or her body weight each day.

Blue bubbles: incoming flow of fluid and nutrients.

Yellow bubbles: fluids secreted by the intestine

Healthy Intestine

Absorption and secretion in the normal intestine are balanced:

» Villi are mature and equipped for absorption

» The majority of incoming fluid is absorbed into the body, delivering nutrition and hydration

» Only a very small amount of fluid is lost with stool

MVID Intestine

Absorption and secretion in the MVID intestine are not balanced:

» Villi are immature and lack absorptive capacity

» The majority of incoming fluid passes through the intestinal tract, and critical nutrients and hydration are not absorbed into the body

» Secretion is exaggerated, so a significant volume of fluid is build up in the intestine – leading to severe diarrhea

Lethal dehydration

The constant loss of fluid from the MVID intestine also creates lethal levels of dehydration. Think of the body as a solution with a high concentration of water, and low concentration of salt. When water is lost due to dehydration, the salt remains, and becomes increasingly concentrated. The salt concentration can reach toxic levels, killing cells in the body.

A washing machine with no drainage holes

Think of the intestine as a washing machine: a typical washing machine controls and directs the removal of detergent and water through drainage holes in the drum. Similarly, a healthy intestine has many tiny holes that control the movement of water and salts across the intestinal wall.

An MVID intestine essentially has no drainage holes, causing it to overflow with fluid (therefore leading to diarrhea). The washing machine drum in this case would look more like a large cooking pot. The “drainage holes” do not develop because of the MYO5B genetic mutation, and the resulting deficiency in a protein called myosin VB.

Diagnosis and prevalence