Megaloblastic anemia

Dr.Himanshu S Dave
DCH,DNB (Final) Pediatrics
NRCH, New Delhi

 Group of disorders caused by impaired DNA
synthesis .
 Red blood cells (RBCs) are larger than
normal at every developmental stage.
 There is maturational asynchrony between
the nucleus and cytoplasm of erythrocytes.

 Myeloid and platelet precursors are also
affected: Giant meta myelocytes and
neutrophil bands are often present in the
bone marrow.
 Thrombocytopenia and leukopenia are often
associated.

 P/S: Large, often oval RBCs with increased
mean corpuscular volume.
 Neutrophils are hypersegmented, with many
having >5 lobes.
 Childhood megaloblastic anemia result from
a deficiency of folic acid or vitamin B12
(cobalamin), vitamins essential for DNA
synthesis. Rarely caused by inborn errors of
metabolism.

CAUSATIVE CONDITIONS HEMATOLOGIC FEATURES
MEGALOBLASTIC ANEMIA
* Cobalamin (vitamin B12 )
deficiency
* Folate deficiency
* Antifolate drugs (e.g.,
methotrexate)
* Cytotoxic drugs (e.g.,
hydroxyurea, 5-FU)
* Immunosuppressive drugs (e.g.,
azathioprine)
* Thiamine-responsive anemia
* Hereditary orotic aciduria
•Megaloblastic changes
(hypersegmented neutrophils)
* Macrocytosis .
* Mild reticulocytopenia
* Pancytopenia (severe cases)

DISORDERS OF ERYTHROID
PRODUCTION
•Aplastic anemia
•PRCA
•Blackfan-Diamond anemia
•Some sideroblastic anemias
•Dyserythropoiesis
•Fanconi anemia
•Myelodysplasia
•Myeloproliferative Diseases
•Nonmegaloblastic
•Some disorders feature
dyserythropoiesis
•Hyposegmented neutrophils.
•Macrocytosis can often be
severe (e.g., aplastic processes).
•Reticulocytopenia (often
severe)

RETICULOCYTOSIS
Chronic hemolytic anemia •Nonmegaloblastic
•No hypersegmented neutrophils
DRUGS AND TOXINS
•Alcohol abuse
•Antiviral drugs (e.g., nucleoside
RT inhibitors)
•Anticonvulsant drugs

NONHEMATOLOGIC DISEASES
•Chronic liver diseases
•Hypothyroidism
•Copper deficiency
•Nonmegaloblastic
ARTIFACTS
* RBC clumping by cold
agglutinins; some
warm RBC antibodies
•Severe hyperglycemia
•Hyponatremia
•Nonmegaloblastic
•Disparity between high MCV and
normal morphologic examination

 Folic acid (pteroylglutamic acid) consists of
pteroic acid conjugated to glutamic acid.
 Biologically active folates: Derived from
folic acid ;serve as 1-carbon donors and
acceptors in many biosynthetic pathways.
 To form functional compounds, folates must
be reduced to tetrahydrofolates in a process
catalyzed by the enzyme dihydrofolate
reductase.

 Essential for DNA replication and cellular
proliferation.
 Humans cannot synthesize folate and depend
on dietary sources, including green
vegetables,fruits, and animal organs (e.g.,
liver, kidney).
 Folates are heat labile and water soluble.

 Naturally occurring folates are in a
polyglutamated form that is less efficiently
absorbed than the monoglutamate species
(i.e., folic acid).
 Dietary folate polyglutamates are hydrolyzed
to simple folates
Absorbed primarily in the proximal small
intestine by a specific carrier-mediated
system.

 Folates travel in the bloodstream
 Taken up in cells primarily in the form of
unconjugated MTHF
 Which is subsequently reconjugated
(polyglutamated) in the cell.

 Rarely, megaloblastic anemia as a
consequence of folate deficiency has its peak
incidence at 4-7 mo of age, somewhat earlier
than iron-deficiency anemia.

Inadequate Nutrition
 Poor diet (Relative dietary insufficiency)
 Poor food preparation methods
 Exclusive feeding with goat's milk

Defects in Absorption
 Gastric achlorhydria
 Diseases of the upper small intestine
-Tropical sprue
-Celiac disease
-Dermatitis herpetiformis
-Inflammatory bowel disease
 Oral pancreatic replacement therapy
 Hereditary folate malabsorption

Increased Requirements or Losses
 Pregnancy
 Lactation
 Prematurity
 Chronic hemolytic anemia
 Dialysis
 Hyperthyroidism
 Lesch-Nyhan syndrome

Disorders of Transport
 Cerebral folate deficiency (genetic or
acquired)
Disorders of Cellular Metabolism
 Drugs inhibiting folate metabolism
-Antifolates (e.g., methotrexate)
-Pyrimethamine
-Trimethoprim
-Sulfasalazine
-Valproic acid

 Inherited defects
- Methylenetetrahydrofolate reductase
(MTHFR) deficiency
- Methionine synthase deficiency
- Dihydrofolate reductase deficiency
- Methylenetetrahydrofolate
dehydrogenase, cyclohydrolase, and
formyltetrahydrofolate synthetase 1
(MTHFD1) deficiency

Multifactorial or Uncertain Mechanisms
 Alcohol abuse
 Anticonvulsants
 Oral contraceptives

 Usually occurs in the context of increased
vitamin requirements associated with
pregnancy, periods of accelerated growth,
and chronic hemolysis.
 Folate requirements greatly increase during
pregnancy, in part to meet fetal needs.

 Folate supplementation is recommended
from the start of pregnancy to prevent
neural tube defects and to meet the needs
of the developing fetus.
 Fortunately, folate-deficient mothers
generally do not give birth to infants with
clinical folate deficiency because there is
selective transfer of folate to the fetus via
placental folate receptors.

 Human breast milk, infant formulas, and
pasteurized cow's milk provide adequate
amounts of folic acid.
 Goat's milk is folate deficient, and
supplementation must be given when it is
the child's main food.
 Powdered milk may also be a poor source of
folic acid.

 Malnutrition is the most common cause of
folate deficiency in older children.
 Those with hemoglobinopathies, infections,
or malabsorption are at increased risk.
 Because body stores of folate are limited,
deficiency can develop quickly in
malnourished individuals.
 On a folate-free diet, megaloblastic anemia
will occur after 2-3 mo.

 Malabsorption caused by chronic diarrheal
states or diffuse inflammatory disease.
 In both situations: Impaired folate conjugase
activity.
 Chronic diarrhea also interferes with the
enterohepatic circulation of folate;
enhancing folate losses because of rapid
intestinal passage.

 Celiac disease or chronic infectious enteritis
and in association with enteroenteric
fistulas.
 Previous intestinal surgery.
 Anticonvulsant drugs (phenytoin, primidone,
phenobarbital) impair folic acid absorption.
 Alcohol overuse

 Rare , but can be life threatening.
Hereditary folate malabsorption (HFM):
 Autosomal recessive disorder
 Several loss-of-function mutations in the
SLC46A1 gene encoding the protein-coupled
folate transporter.

 Inability to absorb folic acid, 5-
tetrahydrofolate, 5-methyltetrahydrofolate,
or 5-formyltetrahydrofolate (folinic acid).
 It can become apparent at 2-6 mo of age
with megaloblastic anemia and other
deficits, including infections and diarrhea.

Neurologic abnormalities:
 Seizures, developmental delay, and
intellectual disability.
 Folate transport is impaired both in the
intestine and at the brain's choroid plexus.
 Serum and cerebrospinal fluid (CSF) folate
levels are very low, with a loss of the normal
3:1 ratio of CSF to serum folate.

Treatment of HFM:
 Involves parenteral folate, although oral
administration has been useful in some
cases.
 Reduced folates are more effective than folic
acid.
 Folate sufficiency should be maintained in
both blood and CSF to avoid important
complications.

Functional methionine synthase deficiency:
 Result from mutations affecting the function
of methionine synthase reductase or
methionine synthase.
 Autosomal recessive.
 Megaloblastic anemia, cerebral atrophy,
nystagmus, blindness, and altered muscle
tone.
 Respond to hydroxocobalamin plus betaine.

Dihydrofolate reductase (DHFR) deficiency:
 Extremely rare.
 Homozygous mutations in the DHFR gene.
 Megaloblastic anemia and neurologic
manifestations

Methylenetetrahydrofolate reductase
(MTHFR) deficiency:
 Most common inborn error of folate
metabolism.
 Severe cases produce neurologic and vascular
complications.
 No associated megaloblastic anemia.

 Anti–folic acid activity & regularly produce
megaloblastic anemia.
 Methotrexate binds to dihydrofolate
reductase and prevents formation of
tetrahydrofolate, the active form of folate.

 Pyrimethamine used in toxoplasmosis, and
Trimethoprim, used for treatment of
various infections, can induce folic acid
deficiency and occasionally megaloblastic
anemia.
 Therapy with folinic acid (5
formyltetrahydrofolate) is usually beneficial

 Features associated with anemia.
 Infants and children : Irritability, chronic
diarrhea, and poor weight gain.
 Hemorrhages from thrombocytopenia may
occur in advanced cases.

 Congenital folate malabsorption associated
with hypogammaglobulinemia, severe
infections, failure to thrive, neurologic
abnormalities, and cognitive delays.

 The anemia is macrocytic (mean corpuscular
volume >100 fL).
 Variations in RBC shape and size.
 Reticulocyte count is low, and nucleated
RBCs with megaloblastic morphology are
often seen in P/S.

 Neutropenia and thrombocytopenia may be
present, in long-standing and severe
deficiencies.
 Neutrophils: Large with hypersegmented
nuclei.
 Bone marrow is hypercellular because of
erythroid hyperplasia, and megaloblastic
changes are prominent.

 Large, abnormal neutrophilic forms (giant
metamyelocytes) with cytoplasmic
vacuolation are also seen.
 Normal serum folic acid levels are 5-20
ng/ml.
 Deficiency: <3 ng/mL.
 Levels of RBC folate are a better indicator
of chronic deficiency.

 Normal RBC folate level : 150-600 ng/mL of
packed cells.
 Levels of iron and vitamin B12 in serum
usually are normal or elevated.
 Serum lactate dehydrogenase (a marker of
ineffective erythropoiesis) is markedly
elevated.

 Folic acid ; orally or parenterally at 0.5-1.0
mg/day.
 If the specific diagnosis is in doubt, smaller
doses of folate (0.1 mg/day) may be used for
1 wk as a diagnostic test (because a
hematologic response can be expected
within 72 hr).

 Doses of folate >0.1 mg can correct the
anemia of vitamin B12 deficiency but might
aggravate any associated neurologic
abnormalities.
 Folic acid therapy (0.5-1.0 mg/day) should
be continued for 3-4 wk until a definite
hematologic response is seen.

 Maintenance therapy with a multivitamin
(containing 0.2 mg of folate) is adequate.
 Very high doses of folate may be required in
the setting of HFM.
 Transfusions are indicated only when the
anemia is severe or the child is very ill.

 FIGLU Test: Excretion of Formimino Glutamic
acid in urine after loading with Histamine.
 Positive FIGLU test is diagnostic of folic acid
deficiency. (Now only theoritical
significance).

 Generic term for all biologically active
cobalamins.
 Water-soluble with a central, functional
cobalt atom and a planar corrin ring.
 Methylcobalamin and adenosylcobalamin are
the metabolically active derivatives, serving
as cofactors in 2 essential metabolic
reactions:

1) Methylation of homocysteine to
methionine (via methionine synthase).
2) Conversion of methyl-malonyl-
coenzyme A (CoA) to succinyl CoA (via L -
methyl-malonyl- CoA mutase).
• The products and by-products of these
enzymatic reactions are critical to DNA, RNA,
and protein synthesis.

 Synthesized exclusively by
microorganisms.
 Humans rely on dietary sources (animal
products, including meat, eggs, fish, and
milk) for their needs.
 Unlike folate, older children and adults have
sufficient vitamin B12 stores to last 3-5 yr.

 In young infants born to mothers with low
vitamin B12 stores, clinical signs of Cbl
deficiency can become apparent in the 1st 6-
18 mo of life.

 Cobalamin is released from food protein in
the stomach through peptic digestion
 Cbl then binds to haptocorrin (HC), a salivary
glycoprotein
 This complex moves into the duodenum,
where HC is digested by pancreatic proteases
and Cbl is liberated

 Cbl then binds to intrinsic factor (IF),
another glycoprotein that is produced by
gastric parietal cells
 The Cbl-IF complex subsequently enters
mucosal cells of the distal ileum by receptor
mediated endocytosis.

 The IF-Cbl receptors are composed of a
complex of 2 proteins, cubilin (CUBN) and
amnionless (AMN), collectively known as
cubam.
 After internalization into enterocytes, IF is
degraded in the lysosome, and Cbl is
released.

 The transporter ABCC1 (also known as MRP1)
exports Cbl bound to the transport protein
transcobalamin (TC), out of the cell.
 In the bloodstream, Cbl is associated with
either TC (approximately 20%) or HC.
 TC mediates the transport of B12 across cells
after complexing with the TC receptor, which
is internalized in the lysosome.

 Lysosomal degradation of TC releases Cbl,
which remains in the cell and is further
processed.
 Two distinct membrane proteins transport
Cbl across the lysosomal membrane into the
cytoplasm.

 Cobalamins are processed in the cytoplasm
 Form a common intermediate
 That can be allocated to the
methylcobalamin and adenosylcobalamin
synthesis pathways to meet cellular needs.

 It is postulated that the MMACHC protein, a
product of the Cbl C locus, accepts the
cobalamins exiting the lysosome.
 HC may play a role in B12 storage.

 Vitamin B12 deficiency in infants is most
often nutritional, due to low Cbl levels in the
breast milk of B12 -deficient mothers.
 Associated megaloblastic anemia often
appears during the 1st yr of life.
 Maternal deficiency may be caused by
pernicious anemia or gastrointestinal
disorders ,previous gastric bypass surgery,
treatment with PPI, or inadequate intake
from a strict unsupplemented vegetarian
diet.

 Fortunately, as a result of active placental
Cbl transport in utero, most children of B12 -
deficient mothers maintain Cbl levels
sufficient to support adequate prenatal
development.
 Such infants are born with low B12 stores.

 Vitamin B12 replacement often results in
rapid improvement, but the longer the
deficient period, the greater the likelihood
of permanent disabilities.
 Neonatal screening programs may detect
maternal neonatal nutritional B12 deficiency:
increase in propionyl carnitine or
measurement of methylmalonic acid (higher
sensitivity).
 Daily requirements range from 0.4-2.4 μg.

 Gastric surgery or medications that impair
gastric acid secretion may result in IF
deficiency, leading to decreased vitamin B12
absorption.
 Pancreatic insufficiency lead to Cbl
deficiency because of impaired cleavage and
IF complex formation.

 Patients with neonatal necrotizing
enterocolitis, inflammatory bowel disease,
celiac disease, or surgical removal of the
terminal ileum.
 An overgrowth of intestinal bacteria within
diverticula or duplications of the small
intestine causes vitamin B12 deficiency by
consumption of (or competition for) the
vitamin or by splitting of its complex with IF

 In these cases, hematologic response can
follow appropriate antibiotic therapy.
 Fish tapeworm Diphyllobothrium latum
infestatation of upper small intestine,
similar mechanisms may be operative.

 Rare autosomal recessive disorder.
 Caused by a variety of mutations in the IF
gene that produce a lack of gastric IF or a
functionally abnormal IF.
 HIFD differs from typical adult pernicious
anemia in that gastric acid is secreted
normally and the stomach is histologically
normal.

 Not associated with antibodies or endocrine
abnormalities.
 Occasionally associated with proteinuria.
 Symptoms become prominent at an early age
(6-24 mo), consistent with exhaustion of
vitamin B12 stores acquired in utero.
 Weakness, irritability, anorexia, and
listlessness occur.
 The tongue is smooth, red, and painful.

 Neurologic manifestations: axia,
paresthesias, hyporeflexia, Babinski
responses, and clonus.
 Oral vitamin B12 is usually ineffective , and
lifelong intramuscular (IM) or intranasal Cbl
should be used to bypass the absorption
defect.

 The natural form, hydroxocobalamin
(OHCbl), is believed to be more effective
than the synthetic form, cyanocobalamin
(CNCbl).

 Recessively inherited.
 Selective vitamin B12 malabsorption in the
ileum and consequent vitamin B12
deficiency.
 Clinically apparent within the 1st 6 yr of life.

 Also have neurologic defects (e.g.,
hypotonia, developmental delay, brain
atrophy, movement disorders, dementia)
and/or proteinuria.
 Mutations in either CUBN or AMN, proteins
that form the cubam receptor for the ileal
IF-Cbl complex.

 CUBN is also a key receptor for protein
reabsorption in the kidney, impaired
expression at this site results in associated
proteinuria.
 The disease is fatal if untreated.
 Early diagnosis and treatment with IM or
intranasal Cbl will reverse the hematologic
and neurologic abnormalities.
 Proteinuria does not respond to therapy.

 Classic pernicious anemia (autoimmune
gastritis) usually occurs in older adults but
can rarely affect children.
 Juvenile pernicious anemia usually presents
during adolescence.

 Antibodies +, against IF and the H+ K+ ATPase
proton pump in gastric parietal cells.
 Immunologic abnormalities, cutaneous
candidiasis, hypoparathyroidism,atrophy of
the gastric mucosa and achlorhydria may
occur.
 IM or intranasal vitamin B12 should be
administered regularly.

 Rare cause of megaloblastic anemia.
 Autosomal recessive.
 Resulting in a failure to absorb and transport
vitamin B12 .
 Most patients lack TC but some have
functionally defective forms.

 Manifests in the first weeks of life.
 Failure to thrive, diarrhea, vomiting,
glossitis, neurologic abnormalities, and
megaloblastic anemia.
 The diagnosis can be difficult. Total serum
vitamin B12 levels are often normal because
approximately 80% of serum Cbl is bound to
HC.

 The diagnosis is suggested bythe presence of
severe megaloblastic anemia in the face of
normal folate levels and no evidence of
another inborn error of metabolism.
 Plasma homocysteine and methylmalonic
acid levels are elevated.
 A definitive diagnosis is made by measuring
plasma TC.

 The serum vitamin B12 levels must be kept
high to force enough Cbl into cells and allow
normal function using high-dose oral
supplementation or IM or intranasal
treatment.

 The conversion of Cbl to methylcobalamin
(MeCbl) and adenosylcobalamin (AdoCbl)
involves a number of steps, abnormalities of
which have been tied to several distinct
alphabetically labeled disorders.
 In CblE and CblG, defective N5-
methyltetrahydrofolate-homocysteine
methyltransferase fails to produce MeCbl.

 Infants with megaloblastic anemia, vomiting,
and developmental delay have
homocystinuria & hyperhomocysteinemia.
 They do not have methylmalonic aciduria or
methylmalonic acidemia.
 Good response to CNCbl.

 AdoCbl and MeCbl are both affected by CblC
(the most common of the Cbl inborn errors),
CblD, and CblF.
 Patients can present in early infancy through
adolescence.
 Newborns have lethargy, failure to thrive,
and neurologic problems.
 Older patients may present with neurologic
difficulties, dementia, and psychological
problems.

 Megaloblastic anemia occurs in about half
the cases.
 Patients have elevated homocysteine and
methylmalonic acid in both urine and blood.
 Affected individuals respond partially to
OHCbl or CNCbl.

 CblA, CblB, and CblH are associated with
methylmalonic aciduria and a variety of
serious symptoms, but megaloblastic anemia
is absent.

 Cbl deficiency present with nonspecific
manifestations:as weakness, lethargy,
feeding difficulties, failure to thrive, and
irritability.
 Other findings include : Pallor, glossitis,
vomiting, diarrhea, and icterus.

 Neurologic symptoms can include
paresthesia, sensory deficits, hypotonia,
seizures, developmental delay,
developmental regression, neuropsychiatric
changes, and brain/spine MRI changes.
 Neurologic problems from vitamin B12
deficiency may occur in the absence of any
hematologic abnormalities.

 The hematologic manifestations of folate and
Cbl deficiency are identical.
 The anemia is macrocytic, with prominent
macro ovalocytosis of the RBCs.
 The neutrophils may be large and
hypersegmented.
 In advanced cases, neutropenia and
thrombocytopenia can occur, simulating
aplastic anemia or leukemia.

 Serum vitamin B12 levels are low.
 Serum methylmalonic acid and homocysteine
are usually elevated.
 Concentrations of serum iron and serum folic
acid are normal or elevated.

 Serum lactate dehydrogenase activity is
 markedly increased (a reflection of
ineffective erythropoiesis).
 Moderate elevations of serum bilirubin levels
(2-3 mg/dL) may be found.
 Excessive excretion of methylmalonic acid in
the urine (normal: 0-3.5 mg/24 hr) is a
reliable and sensitive index of vitamin B12
deficiency.

 A comprehensive medical history is essential
to the clinical recognition of possible Cbl
deficiency.
 Information regarding clinical symptoms,
dietary history, diseases, surgeries, or
medications is important.
 The physical examination may reveal
relevant findings such as irritability, pallor, or
specific neurologic symptoms.

 Screening laboratory findings.
 More focused testing will be required to
confirm a diagnosis of vitamin B12 deficiency
and its cause.
 Cbl deficiency is usually identified by
measuring total or TC bound vitamin B12 in
the blood.

 An extremely low level is generally
diagnostic. (<100 pg/ml)
 False negatives and false positives are
reportedly common using currently available
assays.
 In the face of clinical symptoms, macrocytic
anemia, an abnormal blood smear,and a
normal folate level; Vitamin B12 deficiency is
to be suspected.

 In untreated patients, methylmalonic acid
and total homocysteine levels are often
greatly elevated.
 Excessive urinary methylmalonic acid
excretion (3.5 mg/day) is also a sensitive test
of B12 deficiency.
 Although modest increase occur with renal
failure, elevated methylmalonic acid is
otherwise quite specific for B12 deficiency.

 Notably,serum homocysteine is also elevated
in folate deficiency, homocystinuria, and
renal failure.
 In no evidence of inadequate dietary intake
or, an infant, inadequate maternal B12 ,
malabsorption should be investigated.
 In the past the Schilling test, a measure of
Cbl absorption, was the gold standard, but it
is no longer available.

 Anti-IF antibodies and anti–parietal cell
antibodies are useful for the diagnosis of
pernicious anemia.
 Measurement of IF may be required for less
common disorders.

 Used to establish presence of B12 deficiency
(Part 1) as well as to differentiate between
IF deficiency and mal absorption defects
(Part 2).
 PART -1 : A small amount of radio labelled
(57CO) Vitamin B 12 is given orally, followed
by second flushing dose of 1 mg parenteral
B12 after 2 hours, which leads to excretion
of > 10-30% of radio labelled dose in urine.

 Excretion of < 2% of radio labeled vitamin
B12 indicates its retention in body due to
vitamin B 12 deficiency.
 PART- 2: Test is repeated with 30 mg of IF
given along with radioactive dose. Correction
of test results indicates IF deficiency , while
persistent abnormality suggests mal
absorption.

 The physiologic requirement for vitamin B12
is about 1-3 μg/day.
 Parenteral B12 @ 1 mg (1000 mcg) IM.
 Lower doses @ 250 mcg in infants.
 A decrease in MCV , reticulocytosis, high
platelet and neutrophil counts is observed
within few days of therapy.

 In pernicious anemia and malabsorptive
states , Vitamin B 12 @ 1000 mcg should be
given IM daily for 2 weeks , then weekly
until hematocrit is normal and then monthly
for life.
 In neurological complications: 1000 mcg
everyday for 2 weeks, then every 2 weeks for
6 months and then monthly for life.
 Oral absorption is variable.

Megaloblastic anemia

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