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Iron-Refractory Iron Deficiency Anemia (IRIDA)

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Definition

• Microcytic, hypochromic anemia
• Complete refractoriness to oral iron therapy
• Slow or partial response to parenteral (intravenous) iron
• Inappropriately elevated hepcidin levels relative to iron stores

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Genetics

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Molecular Pathophysiology

Normal Iron Regulation

1. Hepcidin (encoded by HAMP) is the master regulator of systemic iron homeostasis, produced by hepatocytes
2. Hepcidin binds to and induces internalization/degradation of ferroportin (the only known cellular iron export protein), found on duodenal enterocytes and macrophages
3. When hepcidin is elevated: ferroportin is degraded → iron is trapped inside enterocytes and macrophages → less iron enters plasma → iron-restricted erythropoiesis
4. When hepcidin is low (iron-deficient states): ferroportin is upregulated → increased intestinal absorption and macrophage iron release

The BMP-SMAD-HJV Pathway (Hepcidin Activation)

• BMP ligands (particularly BMP6) bind to BMP receptors along with the co-receptor hemojuvelin (HJV) on hepatocyte surfaces
• This activates the SMAD1/5/8 signaling cascade, which enters the nucleus and drives HAMP (hepcidin) gene transcription

Role of Matriptase-2 (TMPRSS6)

• Matriptase-2 is a protease that cleaves HJV from the hepatocyte surface, thereby dampening the BMP-SMAD pathway
• In conditions of iron deficiency, matriptase-2 is upregulated, HJV is cleaved, BMP signaling is reduced, and hepcidin falls - allowing maximum iron absorption
• In IRIDA: loss-of-function mutations in TMPRSS6 → non-functional matriptase-2 → HJV remains intact → BMP-SMAD pathway is constitutively active → inappropriately high hepcidin production even in the face of iron deficiency
• Elevated hepcidin → ferroportin degradation on enterocytes → iron retained within enterocytes, cannot be exported to plasma → functional block of intestinal iron absorption
• Oral iron is absorbed into enterocytes but cannot be exported across the basolateral membrane into the circulation
• IV iron bypasses this block (delivered directly to plasma), explaining the partial response to parenteral iron

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Clinical Features

Presentation

• Can present at any age from infancy to adulthood, but often detected in childhood or early adulthood
• More severe cases tend to present in infancy/childhood
• Female predominance (due to additional iron demands from menstruation)
• Symptoms of chronic anemia: fatigue, pallor, exercise intolerance, poor growth (in children)
• No response to oral iron supplements - this is the hallmark clinical clue

Physical Examination

• Pallor
• Tachycardia in moderate-severe anemia
• Absence of signs of GI pathology (no malabsorption signs)
• Sometimes associated with alopecia (hair loss) - documented in mouse models and some human cases

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Laboratory Findings

Diagnostic Biomarker

• A TSAT/hepcidin ratio that is very low strongly suggests IRIDA vs. regular IDA
• In regular IDA: low iron → low hepcidin → TSAT/hepcidin ratio is normal-to-high
• In IRIDA: low iron + high hepcidin → very low TSAT/hepcidin ratio
• Studies show this ratio has an AUC of ~0.88 for discriminating IRIDA from other causes of IDA, as noted in a 2022 study on transferrin saturation/hepcidin ratio discrimination

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Diagnosis

Diagnostic Criteria

1. Microcytic hypochromic anemia
2. Very low TSAT (often <5%)
3. Low-normal ferritin
4. No/poor response to oral iron (after adequate trial)
5. Partial response to IV iron
6. Elevated hepcidin despite iron deficiency
7. Confirmation: biallelic pathogenic mutations in TMPRSS6 (genetic testing)

Differential Diagnosis

• Hepcidin is inappropriately high (should be low in iron deficiency)
• No response to oral iron despite compliance
• Family history (autosomal recessive - siblings may be affected)
• No identifiable cause of IDA (no GI blood loss, no malabsorption syndrome)

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Treatment

Intravenous (IV) Iron

• First-line treatment for IRIDA
• Bypasses the blocked intestinal ferroportin, delivering iron directly into plasma
• Common preparations: ferric carboxymaltose, iron sucrose, low-molecular-weight iron dextran
• Response is typically partial - hemoglobin improves but may not normalize
• Repeat dosing is often required (every few months in severe cases)
• Hepcidin remains elevated even after IV iron, so effect is sustained only while iron load is being processed via macrophage recycling pathways

Oral Iron

• Ineffective - do not use as sole therapy
• Some very mild/heterozygous cases may show a partial response to high-dose oral iron, but this is not reliable

Supportive Management

• Folic acid supplementation in some cases
• Address any co-existing nutritional deficiencies
• In women: manage menstrual blood loss to reduce iron demand

Monitoring

• Hemoglobin, ferritin, TSAT at regular intervals
• Hepcidin levels to guide treatment
• Symptom assessment

Emerging/Experimental Therapies

• Anti-hepcidin antibodies / hepcidin antagonists: Block hepcidin action, potentially restoring ferroportin function and iron absorption
• TMPRSS6 upregulators: Theoretically boost matriptase-2 expression; currently experimental
• The same TMPRSS6 pathway is being investigated as a therapeutic target (inhibition) in disorders of iron overload such as beta-thalassemia (to increase hepcidin)

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Mouse Models

• Tmprss6-knockout mice develop a phenotype closely mirroring human IRIDA: severe microcytic anemia, hepatic hepcidin overexpression, alopecia
• Duodenal enterocytes of knockout mice show decreased basolateral ferroportin protein - iron is retained within enterocytes, confirming the pathomechanism
• Both the anemia and alopecia were rescuable by iron administration in these models

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Epidemiology and Clinical Relevance

• IRIDA is rare - exact prevalence unknown, but cases reported across multiple ethnicities worldwide
• Often underdiagnosed or misdiagnosed as refractory common IDA
• Patients frequently undergo unnecessary invasive workup (endoscopy, bone marrow biopsy) before the diagnosis is considered
• Recognizing IRIDA prevents costly, unhelpful investigations and directly changes management (oral iron → IV iron)
• TMPRSS6 variants in the general population may contribute to genetic susceptibility to iron deficiency even without full IRIDA - heterozygous carriers may have lower iron stores, especially with co-existing risk factors (menstruation, inflammation, infection)

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Summary Table

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1. Entry point - Microcytic, hypochromic anemia with initial iron studies
2. First branch - Confirm typical IDA pattern (low TSAT, low ferritin, high TIBC) vs. other causes of microcytosis (thalassemia, ACD, sideroblastic anemia)
3. Oral iron trial - 3-month adequate-dose trial; good responders exit as common IDA
4. Extended workup - For non-responders: rule out non-compliance, GI blood loss, malabsorption; then measure serum hepcidin and calculate TSAT/hepcidin ratio - the key discriminating step
5. IRIDA confirmation - Inappropriately high hepcidin without inflammation → genetic testing for biallelic TMPRSS6 mutations → confirmed IRIDA → IV iron therapy

• No identifiable cause of IDA after full workup
• Oral iron fails despite compliance
• Hepcidin elevated when it should be suppressed by iron deficiency
• Autosomal recessive family pattern

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Moderate Acute Malnutrition (MAM) in Children - Detailed Overview

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1. Definition and Classification

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2. Global Burden

• ~32.8 million children under 5 years are affected by MAM globally
• In 2022, ~45 million children suffered wasting (6.8% of children under 5), of which ~13.6 million had SAM

• 75% of all wasted children live in Asia; ~22% in Africa

• Over 20% of children under 5 (~148 million) suffer stunting, which overlaps with chronic undernutrition
• MAM is the gateway to SAM - untreated MAM significantly increases risk of progression to SAM and death

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3. Classification Frameworks

Waterlow Classification (Weight for Height / Height for Age)

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4. Etiology and Risk Factors

Primary Causes

• Insufficient caloric/protein intake - inadequate food supply, poverty, food insecurity
• Early/inappropriate weaning - transitioning from breast milk to calorie-dense but protein-poor diets (e.g., carbohydrate-only porridge)
• Poor diet quality - monotonous diets lacking micronutrients (zinc, iron, vitamin A)
• Low birth weight / preterm birth - starting with depleted nutritional reserves

Secondary/Contributing Causes

• Recurrent infections - diarrhea, respiratory infections, malaria, measles all increase catabolism and reduce appetite (the malnutrition-infection cycle)
• Intestinal malabsorption - chronic diarrhea, parasitic infections (Giardia, hookworm), celiac disease
• Inadequate breastfeeding practices
• Poor water, sanitation, and hygiene (WASH) - enteric infections and environmental enteropathy
• Maternal malnutrition - in utero programming and poor breast milk composition
• Socioeconomic factors - poverty, food insecurity, displacement (refugees/humanitarian crises), inadequate caregiving

The Malnutrition-Infection Cycle

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5. Pathophysiology

Protein and Energy Compartments

In MAM (Moderate Wasting / Pre-Marasmic State)

• Caloric deficit develops over weeks to months
• Body mobilizes subcutaneous fat and muscle glycogen as initial energy reserves
• With ongoing deficit, muscle catabolism begins - providing amino acids for gluconeogenesis
• The somatic protein compartment is moderately depleted but not severely
• Visceral protein compartment (albumin) is largely preserved in pure wasting (MAM/marasmus)
• Leptin production falls → stimulates hypothalamic-pituitary-adrenal axis → elevated cortisol → promotes lipolysis and muscle catabolism
• Immune compromise: T-cell mediated immunity is impaired; secretory IgA levels fall; complement components decrease → increased vulnerability to infections
• Gut microbiome alterations have been documented - differences in microbial flora between malnourished and well-nourished children may play a pathogenic role

Comparison of MAM vs Marasmus vs Kwashiorkor

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6. Clinical Features of MAM

Anthropometric

• Weight-for-height Z-score: -2 to -3
• MUAC: 115-125 mm (in 6 months to 5 years)
• Mid-arm muscle circumference: reduced (reflects somatic protein depletion)
• Skinfold thickness: reduced (reflects fat depletion)

Physical Examination

• General: Child is thin but alert and has preserved appetite (distinguishes from kwashiorkor)
• Skin: Dry, pale, slightly lax; mild scaling
• Hair: May be slightly dull; thin
• Muscles: Visibly reduced bulk, particularly in buttocks, thighs, shoulders
• Subcutaneous fat: Reduced in cheeks, limbs, abdomen
• No edema (presence of edema = SAM by definition)
• No hepatomegaly typically
• May have co-existing micronutrient deficiency signs (angular cheilitis from riboflavin, Bitot's spots from vitamin A, pallor from iron deficiency)

Co-morbidities

• Recurrent diarrhea
• Acute respiratory infections
• Malaria
• Anemia (iron, folate, B12)
• Vitamin A, zinc, iodine deficiencies are common co-morbidities

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7. Diagnosis

Step 1 - Screening (Community Level)

• MUAC tape measurement: Simple, low-cost, performed by community health workers
  • Green zone: ≥ 125 mm (normal)
  • Yellow zone: 115-125 mm (MAM)
  • Red zone: < 115 mm (SAM)
• Bilateral pitting edema check: Press thumbs on dorsum of both feet for 3 seconds - pitting = SAM (kwashiorkor)

Step 2 - Anthropometric Confirmation (Health Facility)

• Weight-for-height Z-score (WHZ): Requires weight scale and height board; compared against WHO Child Growth Standards 2006
• MUAC: Confirmatory measurement
• Weight for age and height for age to assess stunting alongside wasting

Step 3 - Clinical Assessment

• Full history: dietary intake, breastfeeding, illness episodes, immunization status
• Appetite test (offer RUTF - ready-to-use therapeutic food; good appetite = MAM / poor = SAM indicator)
• Check for bilateral edema
• Signs of infection (fever, respiratory rate, jaundice)
• Examination for micronutrient deficiency signs

Step 4 - Laboratory Tests (if available)

• Hemoglobin / complete blood count (anemia)
• Blood glucose (hypoglycemia risk in SAM but also MAM with illness)
• HIV testing (where indicated)
• Stool microscopy (parasites)
• Malaria RDT (endemic areas)
• Serum albumin (low in kwashiorkor, normal in MAM/marasmus)

Differential Diagnosis of Wasting in Children

• Chronic infection (TB, HIV)
• Malabsorption (celiac disease, cystic fibrosis, giardiasis)
• Congenital heart disease
• Chronic renal disease
• Inflammatory bowel disease
• Endocrine causes (diabetes mellitus type 1)
• Thalassemia / hemolytic anemias

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8. Management of MAM

Core Principles

Setting

• MAM → Outpatient management (Supplementary Feeding Programme)
• SAM without complications → Outpatient (Community-based Management of Acute Malnutrition - CMAM)
• SAM with complications → Inpatient (Therapeutic Feeding Centre)

Nutritional Treatment

A. Dietary Counselling (All settings)

• Optimize local available foods: animal-source proteins, legumes, fortified cereals, vegetables
• Promote continued breastfeeding in children <2 years
• Increase meal frequency: 5-6 small meals/day
• Improve complementary feeding practices

B. Supplementary Foods (Context-dependent)

• High community prevalence of wasting
• Food insecurity at household/community level
• As part of an integrated care continuum

C. Micronutrient Supplementation

• Vitamin A supplementation (per national schedule; therapeutic dosing if deficiency signs present)
• Iron and folic acid if anemia is confirmed
• Zinc supplementation (especially during diarrheal illness)
• Iodine (via iodized salt)
• Multivitamin formulations in some protocols

D. Treatment of Concurrent Illness

• Antibiotics for confirmed infections (not routinely prophylactic in MAM, unlike SAM)
• Anti-malarial treatment if malaria confirmed
• Antihelminthics (mebendazole/albendazole) if parasitic infection present or in endemic areas
• Oral rehydration for diarrhea
• Vaccination catch-up (especially measles, which causes acute nutritional deterioration)

Modified Dosage Strategy (2023 WHO Innovation)

Community Health Worker (CHW) Role (2023 WHO Endorsement)

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9. Monitoring Response

Frequency

• Weekly or bi-weekly visits during supplementary feeding

Response Criteria (Discharge from MAM programme)

• WHZ > -2 (or MUAC ≥ 125 mm)
• No bilateral edema
• Minimum stay of 8 weeks (to ensure sustained recovery)
• No acute illness

Failure to Respond (Transfer criteria to SAM programme)

• Deterioration: WHZ falls to < -3 or MUAC < 115 mm
• Development of bilateral edema
• Development of medical complications
• No weight gain after 4 weeks

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10. Consequences of Untreated MAM

Short-term

• Progression to SAM (2-3x increased risk)
• Increased mortality from common infections (pneumonia, diarrhea, malaria)
• Prolonged hospitalization

Long-term (if MAM occurs in early life)

• Stunting (impaired linear growth) - permanent height deficit
• Neurocognitive impairment - reduced brain development, lower IQ, poor school performance
• Impaired immunity - increased lifetime susceptibility to infection
• Metabolic programming - paradoxically increased risk of obesity, type 2 diabetes, and cardiovascular disease later in life (if high-energy foods given non-selectively during recovery - the "thrifty phenotype" hypothesis)

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11. Prevention

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12. Recent Evidence

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Summary