Microvillus Inclusion Disease

Slide 1 · Microvillus Inclusion Disease

Cell polarity, brush-border failure, neonatal intestinal disease

Dr Abu Suraih Sakhri

MBBS, MD (Pathology)

www.abusuraihsakhri.com

Slide 2 · Learning objectives

Explain how MYO5B-associated vesicular transport maintains epithelial polarity.

Connect brush-border disruption with neonatal intractable diarrhea and nutritional failure.

Interpret villin, CD10 and electron-microscopic findings in suspected disease.

Differentiate MVID from important congenital and acquired enteropathies.

Slide 3 · Disease identity and terminology

Microvillus inclusion disease (MVID) is also called Davidson disease.

It is a rare inherited disorder of enterocyte membrane trafficking.

Defective brush-border assembly causes a severe disorder of digestion and transport.

Intracellular microvillus-bearing profiles give the disorder its name.

Slide 4 · Where MVID fits among intestinal disorders

Defects of digestion or absorption

Defects of enterocyte polarity / trafficking

Disaccharidase deficiency: Failed terminal carbohydrate digestion.

Abetalipoproteinemia: Defective lipoprotein assembly.

Celiac disease: Immune-mediated villus injury.

MVID: Impaired apical membrane delivery and recycling.

Intestinal epithelial microvilli become abnormal.

Transport failure can be profound even without brisk inflammation.

Slide 5 · Normal enterocyte: Brush-border architecture

Lumen / apical surface

Nucleus

Apical microvilli

Schematic (not histology or electron microscopy)

Slide 6 · What does an intact brush border accomplish?

Apical microvilli increase the effective membrane surface available to the lumen.

Membrane-localized enzymes complete terminal digestion.

Selective transport proteins mediate electrolyte and nutrient flux.

Microvilli require correct apical delivery and retention of membrane cargo.

Slide 7 · A polarized enterocyte separates transport tasks

Apical membrane faces intestinal lumen

Cellular trafficking sorts cargo to destinations

Basolateral domain interfaces with interstitium

Correct localization matters as much as the presence of a transport protein.

Slide 8 · Membrane organization and intestinal function

Apical compartment

Basolateral compartment

Brush border faces digested luminal nutrients.

Contains specialized transporters and hydrolases.

Requires continuous trafficking and renewal.

Supports transfer toward the interstitium.

Maintains distinct sets of membrane proteins.

Loss of polarity compromises vectorial transport.

Slide 9 · Core disease mechanism

Pathogenic MYO5B variants

Defective myosin Vb–mediated trafficking

Disordered apical brush-border assembly

Failed absorption / severe diarrhea

A primary cell-biological defect produces an organ-level intestinal phenotype.

Slide 10 · Inheritance: Autosomal recessive pattern

Classic MYO5B-related MVID follows an autosomal recessive inheritance pattern.

Affected infants usually harbor pathogenic variants in both MYO5B alleles.

Parents may be clinically unaffected carriers.

The molecular diagnosis provides a basis for family counseling.

Slide 11 · MYO5B encodes an actin-based motor

MYO5B gene

Myosin Vb motor protein

Movement / positioning of intracellular cargo

Normal apical membrane composition

Disease-causing disruption affects membrane delivery and retrieval.

Slide 12 · Myosin Vb is more than a structural component

A molecular motor links membrane-carrying compartments to intracellular movement.

Apical cargo must arrive at the correct membrane surface.

Recycling restores or replaces membrane components after internalization.

MYO5B disruption changes where epithelial proteins reside.

Slide 13 · A simplified apical trafficking cycle

Cargo enters intracellular transport route

Directed delivery to apical domain

Surface retention / function

Retrieval and recycling

This diagram is conceptual; Individual vesicle routes are not drawn to scale.

Slide 14 · RAB-associated apical trafficking context

Experimental literature links myosin Vb with RAB8A and RAB11A transport machinery.

This network helps coordinate delivery of selected apical membrane cargo.

Loss of productive coupling can reproduce features of MVID in models.

These details extend beyond the short Robbins disease paragraph.

Slide 15 · Transport protein synthesis versus localization

Protein made but mislocalized

Protein localized correctly

An enterocyte may still express a transporter.

The protein may accumulate in inappropriate compartments.

Surface function is lost despite residual cellular expression.

Apical sorting delivers cargo to its functional domain.

Vectorial electrolyte and nutrient transport can proceed.

Organization and polarity support the epithelial barrier.

Slide 16 · Brush-border assembly: Normal versus abnormal

Normal polarized enterocyte

MVID enterocyte

Continuous apical brush border

Shortened brush border + intracellular inclusion

Schematic (not histology or electron microscopy)

Slide 17 · What does “microvillus inclusion” mean?

Microvilli or microvillus-like membranes are present inside epithelial cytoplasmic profiles.

These profiles are distinct from an intact luminal brush border.

The source links their accumulation to defective plasma-membrane trafficking.

Electron microscopy demonstrates their diagnostic ultrastructure.

Slide 18 · Conceptual microvillus inclusion in an enterocyte

Lumen / apical surface

Nucleus

Intracytoplasmic microvillus inclusion

Schematic (not histology or electron microscopy)

Slide 19 · From trafficking failure to inclusion formation

Abnormal apical vesicle traffic

Accumulation of vesicular membrane cargo

Intracellular microvillus-bearing profiles

Diagnostic inclusion phenotype

A mechanistic synthesis: The precise cellular origins of inclusions are complex.

Slide 20 · Why terminal digestion is impaired

Brush-border membrane enzymes depend on correct apical organization.

Disorganized microvilli diminish the functional digestive interface.

Digestion products may not be generated or handled normally at the surface.

Defective terminal digestion as one contributor to diarrhea.

Slide 21 · Why transepithelial transport is impaired

Electrolyte and nutrient handling requires properly localized membrane transporters.

MYO5B-related trafficking disturbances alter the apical transport apparatus.

Reduced absorptive capacity can coexist with ongoing epithelial secretory processes.

Net intestinal water balance shifts toward severe luminal fluid loss.

Slide 22 · Linking cell biology to diarrhea

Mislocalization of apical proteins

Nutrient and electrolyte transport imbalance

Excess fluid retained within intestinal lumen

Intractable watery diarrhea

The hallmark symptom is the physiological consequence of failed absorption/transport.

Slide 23 · Malabsorptive and secretory features may coexist

Malabsorptive component

Secretory / electrolyte component

Brush-border digestion and transport are deficient.

Nutrient assimilation is inadequate.

Growth and nutritional status are threatened.

High-volume watery stool may persist despite restricted enteral intake.

Ion and water transport become unbalanced.

Severe sodium and fluid losses may occur.

Slide 24 · Age at onset is diagnostically informative

Severe diarrhea before three months of age.

Manifestations often begin within the first days of life.

Such early onset supports investigation of congenital epithelial disorders.

Age alone is not sufficient for a definitive diagnosis.

Slide 25 · A typical presenting clinical pattern

Intractable, high-volume watery diarrhea in early infancy.

Dehydration can develop rapidly because intestinal fluid losses are continuous.

Feeding intolerance and inability to maintain hydration/nutrition are prominent.

The apparent severity is disproportionate to nonspecific mucosal inflammation.

Slide 26 · Immediate consequences of intestinal failure

Profound stool water and electrolyte losses

Dehydration and acid–base disturbance

Inadequate enteral nutrient absorption

Dependence on parenteral support

Clinical priorities derive directly from the physiologic deficits.

Slide 27 · Metabolic complications: Mechanisms, not cutoffs

Ongoing gastrointestinal losses can deplete total-body water and electrolytes.

Metabolic acidosis is reported with severe neonatal MVID.

Failure to establish adequate enteral nutrition threatens growth.

Individual fluid and electrolyte management requires measured patient data.

Slide 28 · Growth and nutritional consequences

Severe epithelial dysfunction prevents reliable intestinal nutrient delivery.

Failure to thrive may accompany the persistent diarrhea.

Intravenous nutrition can maintain intake but does not repair the epithelial defect.

Clinical care must assess hydration, nutrition and line-related complications.

Slide 29 · Extraintestinal findings require careful attribution

MYO5B variants can be associated with low-GGT cholestatic liver disease.

Parenteral nutrition can independently contribute to hepatobiliary complications.

Hepatic manifestations should not automatically be labeled treatment-induced.

Broader genotype–phenotype relationships are evolving.

Slide 30 · Intestinal and hepatobiliary manifestations

Enterocyte disease

Associated hepatobiliary disease

Apical trafficking disorder with microvillus inclusions.

Profound diarrhea and malabsorption.

Dependence on fluid and nutrition replacement.

Some genotypes alter canalicular transport localization.

Cholestasis may occur independently of parenteral nutrition.

Management requires separating genetic and treatment effects.

Slide 31 · What routine histology may suggest

A small-intestinal biopsy may show villus blunting or atrophy.

Apical enterocyte cytoplasm can be vacuolated or granular.

Surface brush-border attenuation may be patchy.

These light-microscopic features alone are not disease-specific.

Slide 32 · Architecture versus cell-level lesion

Mucosal architecture

Enterocyte brush-border phenotype

Villus shortening can accompany many enteropathies.

Inflammatory changes and crypt responses vary.

Overall villus morphology cannot identify MVID by itself.

Loss of normal sharp apical membrane line.

Subapical cytoplasmic staining/vesicles.

Internalized microvillus-containing structures.

Slide 33 · Periodic acid–Schiff: An explanatory adjunct

Normal apical brush-border staining tends to form a narrow luminal line.

MVID may produce abnormal apical/subapical PAS-positive material.

An expanded cytoplasmic band or granules can prompt closer evaluation.

PAS cannot replace ultrastructural and molecular correlation.

Slide 34 · Normal and MVID PAS staining patterns

Expected normal pattern

Abnormal MVID pattern

Relatively continuous, narrow apical staining.

Localization follows the enterocyte–lumen interface.

No characteristic intracellular microvillus-containing band.

Attenuated or disrupted apical line.

Subapical/apical cytoplasmic PAS-positive accumulations.

Pattern should trigger CD10/villin or EM correlation.

Slide 35 · CD10 immunohistochemistry in MVID

CD10 ordinarily accentuates the intestinal brush-border surface.

In MVID, intracytoplasmic/apical subapical CD10-positive structures may appear.

A broadened, irregular or misplaced CD10 pattern supports a trafficking disorder.

CD10 is an adjunctive morphological marker, not a genotype test.

Slide 36 · CD10: Normal distribution versus MVID

Normal enterocyte

MVID enterocyte

Fine linear surface labeling of the brush border.

Emphasizes the luminal enterocyte margin.

No characteristic internalized staining pattern.

Abnormal apical cytoplasmic or vesicular labeling.

Microvillus inclusion-related structures may stain.

Distribution is interpreted with morphology and clinical context.

Slide 37 · Villin highlights microvillus-related structures

Villin is a brush-border-associated protein.

Villin immunostaining can reveal abnormal internalized apical components.

Loss of the expected crisp apical surface distribution is informative.

The staining pattern complements CD10 and ultrastructural assessment.

Slide 38 · Reasoning from immunostaining to diagnosis

Recognize disrupted apical border

Identify abnormal cytoplasmic apical-marker staining

Correlate with ultrastructure

Confirm with genotype when feasible

A single stained structure is not sufficient without correlation.

Slide 39 · Electron microscopy: Defining lesion

Enterocytes may have shortened, sparse or absent luminal microvilli.

Intracytoplasmic inclusions are lined by microvilli.

Abnormal apical vesicular and tubulovesicular profiles may accumulate.

EM demonstrates topology that routine H&E cannot resolve.

Slide 40 · EM interpretation: Schematic ultrastructural correlate

Normal polarized enterocyte

MVID enterocyte

Continuous apical brush border

Shortened brush border + intracellular inclusion

Schematic (not histology or electron microscopy)

Slide 41 · Do not confuse an inclusion with surface microvilli

Normal microvilli project from the apical membrane into the intestinal lumen.

An inclusion is bounded within the cytoplasm of an enterocyte.

EM helps establish the position and orientation of the membrane structures.

The accompanying reduced brush border strengthens interpretation.

Slide 42 · Sampling effects and diagnostic pitfalls

An abnormal phenotype can be more conspicuous in mature villus enterocytes.

Microvillus inclusions and staining changes may be focal or heterogeneous.

A normal-looking field does not establish absence of disease.

Sampling, fixation and method availability should inform diagnostic confidence.

Slide 43 · Biopsy-based diagnostic reasoning

Early severe diarrhea + intestinal dysfunction

Examine apical enterocyte morphology

PAS / CD10 / villin as available

EM and molecular confirmation

This is a teaching pathway, not a clinical-practice guideline.

Slide 44 · Genetic confirmation and its limits

Biallelic pathogenic MYO5B variants support classic MVID.

Genetic testing can resolve a difficult phenotypic differential.

Variant classification requires appropriate pathogenicity evidence.

A negative or uncertain result should be integrated with histology and clinical data.

Slide 45 · Molecular heterogeneity beyond classic MYO5B

Subsequent research identifies STX3 and STXBP2-related MVID phenotypes.

UNC45A-associated disorders can produce MVID-like enterocyte abnormalities.

The genes converge on epithelial polarity, myosin-related function or apical traffic.

These additional genes are supplementary literature, not part of Robbins’ short paragraph.

Slide 46 · Classical gene and broader differential genes

Classic textbook locus

Broader literature-associated loci

MYO5B → myosin Vb motor.

Core problem: Apical membrane trafficking.

Autosomal recessive disease with early severe diarrhea.

STX3 → apical membrane fusion machinery.

STXBP2 → vesicle fusion machinery; Systemic disease context.

UNC45A → myosin folding/function; MVID-like phenotypes.

Slide 47 · A molecular result is not automatically causal

Assess allele configuration and inheritance for recessive disease.

Distinguish pathogenic / likely pathogenic variants from uncertain significance.

Review whether the phenotype matches a known gene-associated syndrome.

Report concordance and residual uncertainty rather than assigning a diagnosis from a VUS.

Slide 48 · A rational neonatal diagnostic pathway

Severe diarrhea beginning in the neonatal period

Evaluate dehydration, infection and biochemical causes

Investigate congenital epithelial/transport disorders

Biopsy morphology + apical markers ± EM + genetics

Integrate results with multidisciplinary clinical findings

Slide 49 · MVID versus lactase deficiency

MVID

Lactase deficiency

Primary inherited membrane trafficking disorder.

Severe neonatal intractable diarrhea.

Abnormal apical vesicles and brush-border organization.

Intracellular microvillus inclusions are diagnostic clues.

Disaccharidase defect at brush border.

Osmotic symptoms linked to lactose exposure.

Histology usually unremarkable in isolated deficiency.

Symptoms in congenital cases abate with lactose exclusion.

Slide 50 · MVID versus abetalipoproteinemia

MVID

Abetalipoproteinemia

MYO5B-linked trafficking defect in classic disease.

Severe early watery diarrhea and brush-border lesions.

Subapical inclusions on EM; CD10/villin anomalies.

MTTP-linked failure to assemble apoB lipoproteins.

Infant diarrhea, steatorrhea and nutritional deficits.

Lipid-laden vacuolated enterocytes; Acanthocytes may appear.

Slide 51 · MVID versus celiac disease

MVID

Celiac disease

Often manifests within days of birth.

Apical trafficking defect; Inclusions can be detected.

Villus atrophy is possible but not defining in isolation.

Immune-mediated gluten-associated enteropathy.

Typical villous atrophy with increased intraepithelial lymphocytes.

Diagnosis requires suitable serologic–clinical–histologic correlation.

Slide 52 · MVID versus autoimmune enteropathy

MVID

Autoimmune enteropathy

Genetic apical membrane trafficking disorder.

Internalized microvillus structures support its diagnosis.

Severe diarrhea can occur without prominent immune injury.

Immune dysregulation may be associated with IPEX/FOXP3.

Other autoimmunity and epithelial immune damage occur.

Mucosal inflammatory patterns and systemic findings differ.

Slide 53 · MVID versus tufting enteropathy

MVID

Tufting enteropathy

Abnormal apical brush border and intracellular inclusions.

Vesicular trafficking/polarity disease.

EM and apical-marker immunostains help confirmation.

Another congenital epithelial enteropathy.

Focal epithelial surface tufts are a distinctive clue.

EPCAM variants are associated with many cases.

Slide 54 · High-yield congenital diarrhea discrimination

Condition

Biological defect

Most useful discriminator

MVID

Apical trafficking / polarity

Microvillus inclusions; CD10/villin

Congenital lactase deficiency

Lactose hydrolysis

Milk-triggered osmotic diarrhea

Abetalipoproteinemia

ApoB lipoprotein assembly

Enterocyte lipid vacuoles

Tufting enteropathy

Epithelial adhesion

Surface epithelial tufts

Congenital ion transporter defects

Electrolyte absorption/flux

Characteristic stool chemistry/genetics

Slide 55 · Avoid diagnosing from villous atrophy alone

Shortened villi have many different possible etiologies.

Enterocyte-level abnormalities can be more specific than global villus architecture.

Clinical age of onset and mucosal inflammation guide prioritization.

Confirm MVID through a compatible cellular/ultrastructural and/or molecular pattern.

Slide 56 · Case application: Neonatal intractable diarrhea

A newborn develops profuse watery diarrhea in the first postnatal week.

Fluid loss continues despite careful nutritional adjustments.

Small-bowel biopsy demonstrates abnormal subapical CD10 staining.

No alternative acquired cause adequately explains the severity.

What diagnosis and confirmatory examinations are most appropriate?

Slide 57 · Case interpretation: Integrate phenotype and tissue

MVID should be prioritized among congenital epithelial diarrheal disorders.

Subapical CD10 labeling suggests mislocalized brush-border components.

Look for microvillus inclusions on electron microscopy.

Seek a compatible pathogenic genotype; Do not rely on one stain alone.

Slide 58 · Case application: Interpreting electron microscopy

Biopsy from an infant with persistent severe diarrhea is examined ultrastructurally.

Surface microvilli are sparse and shortened.

A membrane-bounded cytoplasmic compartment is lined by microvilli.

Subapical vesicular structures are increased.

Which abnormality best distinguishes this from nonspecific villous injury?

Slide 59 · EM case answer: Location defines the lesion

An intracytoplasmic microvillus-lined inclusion is characteristic of MVID.

Shortened surface microvilli are important supporting evidence.

Correlate the EM phenotype with apical immunostaining and genetics.

Absence of a visible inclusion in one field does not exclude disease.

Slide 60 · Management goals follow the causal pathway

Measure and replace fluid/electrolyte losses

Establish adequate parenteral nutrition

Detect complications of prolonged support

Assess intestinal transplantation candidacy

Treatment supports physiology; It does not restore normal myosin Vb function.

Slide 61 · Parenteral nutrition: Rationale and limits

Severe mucosal dysfunction may prevent adequate enteral fluid/nutrient uptake.

Total parenteral nutrition (TPN) bypasses intestinal absorptive failure.

TPN does not correct the defective brush border or eliminate diarrheal losses.

Long-term care requires specialist monitoring for vascular-access and liver complications.

Slide 62 · Intestinal transplantation in severe MVID

Small-bowel transplantation is a recognized option for profound intestinal failure.

It can provide functioning absorptive intestinal epithelium.

Recipient selection must balance benefit with major surgical and immunologic risks.

Associated liver disease may influence transplant planning.

Slide 63 · Two support strategies have different goals

Total parenteral nutrition

Intestinal transplantation

Supplies fluid, electrolytes and nutrients intravenously.

Maintains growth while bypassing ineffective intestinal absorption.

Prolonged therapy carries infection, access and hepatobiliary risks.

Aims to restore functional intestinal absorption.

May reduce reliance on lifelong parenteral support.

Carries rejection, immunosuppression and procedure-related risk.

Slide 64 · The high-burden complications must be monitored

Recurrent dehydration and electrolyte disturbances from ongoing diarrhea.

Central venous catheter-related complications during TPN.

Nutrition-associated and/or genotype-associated cholestasis.

Growth and developmental outcomes over a prolonged disease course.

Slide 65 · Experimental strategies are not established cures

Cell and animal models clarify myosin Vb-dependent epithelial trafficking.

Research explores ways to restore transporter localization or reduce fluid loss.

Preclinical mechanistic observations are not equivalent to effective infant therapy.

TPN and transplantation remain central clinical approaches in the cited literature.

Slide 66 · Core causal chain to retain

MYO5B-associated trafficking defect

Loss of properly organized apical brush border

Vesicles and microvillus inclusions in enterocytes

Catastrophic intestinal transport failure

Microvillus inclusion disease links molecular cell polarity to a neonatal phenotype.

Slide 67 · Five diagnostic principles

Suspect a congenital epithelial disorder in severe diarrhea beginning within days of birth.

Findings relate to apical enterocyte membrane trafficking—not inflammation alone.

CD10 and villin can disclose internalized brush-border components.

Electron microscopy demonstrates the defining intracellular inclusions.

Interpret pathogenic genotypes in conjunction with phenotype and tissue.

Slide 68 · Final challenge: The misleading biopsy

An infant with watery diarrhea has duodenal villus blunting but little inflammation.

The differential includes congenital epithelial defects and several non-MVID disorders.

A pathologist is asked whether villus atrophy proves MVID.

Only routine H&E sections have been reviewed.

Which additional evidence is needed before a confident MVID diagnosis?

Slide 69 · Final challenge: Expected reasoning

Villus blunting is nonspecific and cannot diagnose MVID.

Interrogate the apical enterocyte phenotype with PAS, CD10 and/or villin.

Seek intracytoplasmic microvillus inclusions by electron microscopy when feasible.

Combine findings with age, course, biochemical workup and molecular testing.

Slide 70 · References: Primary textbook and diagnosis

Robbins, Cotran & Kumar. Pathologic Basis of Disease. 11th ed. 2026; Chapter 17, p. 716.

Jayawardena D et al. F1000Research. 2019;8:2061. Doi:10.12688/f1000research.20762.1.

Kozan EN et al. Gastroenterol Hepatol Bed Bench. 2023;16:234–239. Doi:10.22037/ghfbb.v16i2.2735.

Slide 71 · References: mechanism and molecular spectrum

Goldenring JR, Kaji I. Cell Mol Gastroenterol Hepatol. 2022;14:553–565. doi:10.1016/j.jcmgh.2022.04.015.

Uncovering the Relationship Between Genes and Phenotypes Beyond the Gut in MVID. Cell Mol Gastroenterol Hepatol. 2024;17:983–1005.

Supplementary literature is distinguished from the MYO5B-centered Robbins description in speaker notes.