Microvillous inclusion disease is a rare genetic condition affecting the intestine that appears shortly after birth, causing severe, relentless watery diarrhea and making it impossible for babies to absorb the food and fluids they need to survive.

What Is Microvillous Inclusion Disease?

Microvillous inclusion disease, often abbreviated as MVID, is a rare and serious genetic disorder that affects the small intestine from birth. The condition disrupts the normal structure and function of cells lining the intestine, making it impossible for the body to absorb nutrients and fluids properly. This leads to severe, ongoing diarrhea that begins within hours or days after a baby is born.^[1]

The surface of intestinal cells in a healthy person is covered with tiny finger-like structures called microvilli (very small projections that increase the surface area for absorption). In children with MVID, these microvilli are either missing, malformed, or trapped inside the cells rather than on the surface where they belong. This means that nutrients and water cannot be absorbed as food passes through the intestine.^[2]

The disease was first described in 1978 by a doctor named Davidson, and for some time it was called Davidson’s disease. Over the years, it has also been known as congenital microvillous atrophy or microvillous atrophy. The name “microvillous inclusion disease” comes from a characteristic finding under the microscope: abnormal clumps of microvilli trapped inside intestinal cells, forming what doctors call “inclusion bodies.”^[3]

MVID is classified as a congenital enteropathy (an intestinal disorder present from birth). It is one of several rare conditions that cause severe diarrhea in newborns, though MVID is among the most challenging to manage.^[1]

Epidemiology: How Common Is MVID?

Microvillous inclusion disease is extremely rare. At least 200 cases have been reported in Europe, though the condition occurs worldwide.^[2] Because the disease is so uncommon and difficult to diagnose, the true number of people affected is unknown. Some experts believe that more cases exist than are currently recognized, as babies may be misdiagnosed or may die before a proper diagnosis is made.^[4]

Countries where marriages between close relatives are more common tend to see higher rates of MVID because the disease is inherited in an autosomal recessive pattern (meaning both parents must carry the genetic mutation for a child to develop the condition).^[5]

There appears to be a male predominance with this condition, with boys affected about one and a half times more often than girls. The sex ratio has been reported as approximately 1.5 boys for every 1 girl affected.^[4]

Because of its rarity and the complexity of diagnosis, most children with MVID are cared for at specialized pediatric gastroenterology centers that have experience with congenital intestinal disorders. The scarcity of cases means that knowledge about the disease has developed slowly, though recent genetic discoveries have accelerated understanding.^[3]

Causes of Microvillous Inclusion Disease

MVID is caused by mutations in specific genes that are essential for the normal development and function of intestinal cells. The most common genetic cause is a mutation in the MYO5B gene, which provides instructions for making a protein called myosin Vb. This protein plays a crucial role in determining where different components should be positioned within cells—a property known as cell polarity (the organization and orientation of structures within a cell).^[2]

When the MYO5B gene is mutated, myosin Vb protein either doesn’t function properly or is completely absent. In the cells lining the small intestine, called enterocytes (cells responsible for nutrient absorption), this loss of function disrupts normal cell organization. As a result, enterocytes cannot properly form microvilli on their surface. Instead, small clumps of abnormal microvilli become trapped inside the cells, mixed with digestive proteins, forming the characteristic microvillus inclusions that give the disease its name.^[2]

Not all cases of MVID are caused by MYO5B mutations. Scientists have identified other genes that can cause the disease or variants of it. Mutations in the STX3 gene (which codes for syntaxin 3) can cause a variant form of MVID, sometimes without the typical inclusion bodies seen under the microscope.^[4] Another gene, STXBP2 (also called Munc18-2), can cause MVID when mutated, and interestingly, this gene is also associated with a separate condition called familial hemophagocytic lymphohistiocytosis.^[4] More recently, mutations in the UNC45A gene have also been identified as a cause.^[11]

However, some patients diagnosed with MVID based on their symptoms and microscopic findings do not have mutations in any of the known genes. This suggests that there may be additional genetic causes yet to be discovered.^[4]

Risk Factors

The primary risk factor for microvillous inclusion disease is genetic inheritance. Since MVID follows an autosomal recessive inheritance pattern, the main risk occurs when both parents carry a mutation in one of the genes associated with the disease. If only one parent is a carrier, their children will not develop MVID, though they may become carriers themselves.^[1]

Families with a history of MVID are at higher risk of having additional affected children. In some documented families, more than one child has been diagnosed with the condition, which reflects the 25 percent recurrence risk with each pregnancy when both parents are carriers.^[1]

Populations with higher rates of consanguinity (marriage or reproduction between close blood relatives) face increased risk for all autosomal recessive conditions, including MVID. This is because related individuals are more likely to carry the same rare genetic mutations inherited from common ancestors.^[5]

Unlike many other diseases, MVID has no known environmental, lifestyle, or behavioral risk factors. It is not caused by anything parents did or did not do during pregnancy. The condition is not contagious and cannot be transmitted from person to person. Pregnancy and birth are typically normal in mothers carrying affected babies, offering no warning signs before the infant develops symptoms after birth.^[5]

For families where one child has been diagnosed with MVID, genetic testing and counseling can help identify whether both parents are carriers and assess the risk for future pregnancies. If the specific genetic mutation has been identified in an affected family member, prenatal diagnosis may be possible in subsequent pregnancies, though there are no specific prenatal signs or symptoms that would suggest MVID before genetic testing.^[4]

Symptoms and Clinical Presentation

The symptoms of microvillous inclusion disease typically appear very early in life, though there are two recognized patterns of onset. The early-onset form develops within hours or the first few days after birth, while the late-onset form may not appear until around two to four months of age. Regardless of when symptoms begin, the hallmark feature is severe, watery diarrhea that does not improve.^[4]

The diarrhea in MVID is profuse and intractable, meaning it is extremely difficult to control. Affected infants can produce 100 to 500 milliliters of watery stool per kilogram of body weight each day—a volume comparable to or even greater than what is seen in cholera. This represents an enormous fluid loss for a small baby. The diarrhea is classified as secretory, which means it continues even when the baby is not being fed, persisting despite complete bowel rest.^[11]

Because of these massive fluid losses, babies with MVID become severely dehydrated very quickly. Without aggressive intravenous rehydration, an infant can lose up to 30 percent of their body weight within 24 hours. This rapid dehydration leads to profound metabolic acidosis (a dangerous condition where the body’s fluids become too acidic) and requires immediate hospitalization.^[11]

Food intake makes the diarrhea worse. Attempting to feed the baby increases the frequency and volume of watery stools. This is because the intestine not only fails to absorb nutrients and fluids but also continues to secrete fluid into the intestinal tract. Babies with MVID cannot absorb the nutrients they need from food, leading to severe malnutrition (inadequate nutrition due to lack of proper food or inability to absorb nutrients).^[2]

As a result of malnutrition and the inability to absorb nutrients, affected infants experience failure to thrive (inability to gain weight and grow as expected). They cannot gain weight properly and do not develop normally. Without specialized nutritional support delivered directly into the bloodstream, babies with MVID will not survive.^[4]

Additional symptoms and complications may include developmental delays, though these are often related to the challenges of managing the disease rather than being direct effects of the genetic mutations. Some affected individuals may develop liver and kidney problems over time, particularly related to long-term dependence on intravenous nutrition. Osteoporosis (thinning and weakening of the bones) can develop in some patients. Cholestasis (reduced ability to produce and release bile, a digestive fluid) may occur, potentially leading to irreversible liver disease called cirrhosis (scarring and permanent damage to the liver).^[2]

Rare associated abnormalities have been reported in some cases, including inguinal hernia and renal dysplasia, though these are not consistent features of the disease.^[4]

The late-onset or atypical forms of MVID tend to have milder symptoms. Some children with these variants may be able to tolerate some oral feeding and do not require full-time parenteral nutrition. Individuals with the variant type more frequently survive past childhood.^[2]

Prevention

Because microvillous inclusion disease is caused by inherited genetic mutations, there is no way to prevent the disease itself from developing in an affected child. However, families can take steps to understand their risks and make informed decisions about future pregnancies.

For families where one child has been diagnosed with MVID, genetic counseling is strongly recommended. A genetic counselor (a healthcare professional trained in genetics who helps families understand inherited conditions) can explain the inheritance pattern, assess the risk of recurrence in future pregnancies, and discuss available options. Since MVID follows an autosomal recessive pattern, couples who have had one affected child have a 25 percent chance with each subsequent pregnancy of having another child with the condition.^[1]

Genetic testing can identify whether both parents carry mutations in the genes known to cause MVID. If the specific mutation causing the disease in an affected family member has been identified, prenatal diagnosis becomes possible for future pregnancies. This can be done through procedures such as amniocentesis (testing fluid from around the developing baby) or chorionic villus sampling (testing tissue from the placenta), though these procedures carry small risks and should be discussed thoroughly with healthcare providers.^[4]

It is important to note that prenatal diagnosis for MVID is only possible when the specific genetic mutation has already been identified in a family. There are no routine prenatal signs or symptoms that suggest a baby has MVID, and the condition cannot be detected through standard prenatal ultrasound or other routine pregnancy monitoring. Pregnancy and delivery are typically completely normal.^[4]

For the general population, there are no known lifestyle changes, dietary modifications, vaccinations, or other preventive measures that can reduce the risk of MVID, as the disease is purely genetic in origin. Unlike infectious diseases or conditions related to environmental exposures, MVID cannot be prevented through public health interventions or personal choices made before or during pregnancy.

Research into the disease continues, and recent advances in understanding the genetic causes and mechanisms of MVID may eventually lead to targeted therapies or interventions. Families affected by MVID are encouraged to connect with specialized centers that have expertise in congenital enteropathies, as these centers often participate in research studies and clinical trials aimed at improving outcomes.^[3]

Pathophysiology: What Goes Wrong in the Body

To understand what happens in microvillous inclusion disease, it helps to first understand how the small intestine normally works. The small intestine is where most digestion and nutrient absorption occurs. Its inner surface is lined with specialized cells called enterocytes. These cells have a distinctive structure: their surface facing the intestinal cavity is covered with thousands of tiny projections called microvilli, which together form what is known as the brush border (the fringe-like appearance of microvilli on intestinal cells).^[16]

The microvilli dramatically increase the surface area available for absorption, allowing the intestine to efficiently take in nutrients and fluids from food as it passes through. Special transport proteins embedded in the membranes of these microvilli actively move nutrients, electrolytes, and water from the intestinal cavity into the cells and then into the bloodstream. This is how the body extracts the nourishment it needs from food.^[16]

In MVID, this carefully organized system breaks down at the cellular level. The genetic mutations that cause MVID disrupt the normal polarity and organization of enterocytes. Instead of having properly formed microvilli extending outward from their surface, affected enterocytes either have very short, stubby microvilli, no microvilli at all, or microvilli that are trapped inside the cell rather than on its surface.^[7]

When mutations affect the MYO5B gene, the resulting loss of myosin Vb protein disrupts the trafficking of important cellular components. Myosin Vb normally helps move materials within cells and determines where different proteins and structures should be positioned. Without functional myosin Vb, enterocytes cannot properly deliver the proteins and components needed to build and maintain microvilli to the correct location on the cell surface.^[2]

Inside affected enterocytes, researchers have observed abnormal accumulation of vesicles and granules containing digestive enzymes and transport proteins at the top of the cells. These materials should be incorporated into the brush border but instead accumulate in the wrong place. Microscopic examination reveals the characteristic microvillus inclusions: small clumps of malformed microvilli mixed with misplaced digestive proteins, forming distinct structures inside the cells that can be seen with special staining techniques and electron microscopy.^[3]

The functional consequence of these structural abnormalities is devastating. Without properly formed microvilli and with transport proteins in the wrong locations, enterocytes cannot absorb nutrients, electrolytes, or water. Recent research using patient-derived intestinal cells grown in the laboratory (organoids) has revealed specific details about what goes wrong. Studies have shown that intestinal cells in MVID lose the ability to absorb sodium and the water that normally travels with it. At the same time, secretion of chloride and fluid continues normally. The net result is massive fluid loss into the intestinal cavity, producing the severe, watery diarrhea characteristic of the disease.^[9]

The mutations also affect a process called exocytosis (the cellular process of releasing materials from inside the cell to the outside), leading to impaired delivery of ion channels and transporters to the cell surface. This disrupted trafficking is a common defect across different genetic forms of MVID.^[7]

In the early-onset form of MVID, these cellular abnormalities are present from birth and are severe. In the late-onset form, there may be some residual function that allows partial absorption initially, though progressive dysfunction eventually leads to similar symptoms, albeit less severe.^[4]

Beyond the immediate effects on the intestine, the inability to absorb nutrients has cascading effects throughout the body. Without adequate nutrition absorbed through the intestine, affected individuals depend entirely on parenteral nutrition (intravenous delivery of nutrients directly into the bloodstream, bypassing the digestive system). While this life-saving intervention provides necessary nutrition, long-term dependence on parenteral nutrition can lead to complications including liver damage, increased risk of infections, and problems with bone health.^[3]

Recent research has provided hope for potential future treatments by revealing more about the underlying mechanisms. Scientists have discovered that certain interventions might help restore some function to affected intestinal cells, though these approaches are still experimental and require much more study before they could become available treatments.^[9]