Alpha Thalassemia is further classified on the number of gene deletions (4 in total):
- Silent carrier(1 gene deletion)
- Alpha trait(2 gene deletion)
- HbH disease(3 gene deletion)
- Alpha thalassemia major/Hydrops fetalis(4 gene deletion)
Beta Thalassemia is classified on basis of chain deletion (2 in total) rather than gene deletion as:
- Beta thalassemia trait(1 chain deletion)
- Beta thalassemia intermedia(2 chain deletion but mild variety)
- Beta thalassemia major(2 chain deletion but severe variety)
SYMPTOMS (seen by parents)
Usually around 4-6 months of age
- Increasing paleness
- Poor feeding
- Abdominal swelling
SIGNS (seen by physician)
- The hallmark of thalassemia is anemia resulting from ineffective erythropoesis
- Marked pallor
- Signs of failure maybe present- tachycardia, tachypnea, hepatomegaly Splenomegaly
Complete blood counts show microcytic hypochromic (Low MCV/MCH) anemia, high white cell count, platelet count maybe raised.
Peripheral smear shows hypochromic microcytic cells, anisocyosis, poikilocytosis, target cells.
Hb electrophoresis is diagnostic. The patients as well as parents testing must be done. This test must be taken prior to blood transfusion. The patients study will show raised HbF and low HbA2 and HbA. The parents study will show raised HbA2 (>3.5%)
The patient has to be managed with regular blood transfusion usually every 3-4 weeks with packed red cells which are leucodepleted. The pre transfusion Hb should not be allowed to fall <9gm/dl.
After around 10-12 transfusions chelation therapy must be started to rid the body of exxcess unusable iron. The iron status is monitored using serum ferritin. If not monitored iron deposition in liver, heart ,brain and other organs leads to failure of working of these organs and eventually death.
Iron is therefore removed using chelation therapy which can be oral/IV. Various drugs used are desferroxamine(IV), deferiprone and desferrasirox (oral). The oldest and yet best drug yet is desferroxamine.
Chelation is continued lifelong and the patient is monitoed of side effects of these drugs- white counts can drop, growth monitoring, hearing tests, liver and kidney functions.
However, the most important aspect of management still remains parent counselling. The parents are dealing with a chronic and incurable disease,hence counselling for further pregnancy is a must. This disease is autosomal recesive and follows mendelian laws of genetics. Hence, in each pregnancy there is a 25% chance of delivering a baby with thalassemia major.
At 16 weeks of pregnancy an amniocentesis is done to test for the genetic mutation causing thalassemaia. This mutation is previously identified in the parents. If the fetus has the mutations, abortion is advised else pregnancy is continued.
PREVENTION IS THE ONLY HOPE FOR THALASSEMIA!!!!!!!!!!!!!!!!!!
Thalassemia Package: Rs. 2200/ per visit (Includes Pediatric Hematologist Consultation, Fully tested Crossmatched Leucoreduced Blood Transfusion, Complete Blood Count and Day Care File).
- Initial dose of 10 μg CNCbl may be given subcutaneously for 2 days. This therapy is sufficient to normalize serum lactate dehydrogenase and iron levels and induce reticulocytosis in 5 to 7 days, but insufficient to normalize plasma methylmalonic acid and total homocysteine levels and replete body stores.
- For severely affected children, the dose of CNCbl is 0.2 μg/kg/day subcutaneously for 2 days.
- Complete correction of megaloblastosis and associated metabolic changes requires anywhere from 15 to 150 μg of CNCbl.
- Conventional therapy has been 1000 μg of CNCbl or OHCbl by injection daily for 1 week, followed by 100 μg of CNCbl weekly for 1 month and then monthly thereafter.
- Oral therapy with 1 to 2 mg cobalamin daily is cheaper and better tolerated and has become standard treatment in many countries
- Whether oral therapy arrests the neurologic toxicity as quickly as parenteral dosing does is not yet known
CAUSES OF B12 DEFICIENCY
- Inadequate intake
- Vegans, poorly controlled PKU diet, malnutrition
- Maternal B12 Deficiency
- Defective Absorbtion
- Failure of IF
- Failure in absorption small intestine
- Defective Transport
- Metabolic Defects
- Failure of IF
- Congenital absence – normal mucosa
- Juvenile PA
- Juvenile PA with polyendocrinopathies
- Juvenile PA with IgA deficiency
- Gastric mucosal disease – corrosives, Gastrectomy
- Failure in absorption small intestine
- Abnormal IF
- Defective IF transport by enterocytes – Imerslund Gräseback syndrome
- Chelating agents. – Bind Ca++
- Generalised malabsorbtion
- Intestinal Resection
- Crohns disease
- Malignancy– lymphosarcoma
- Pancreatic insufficiency
- Zollinger Ellison Syndrome
- Celiac Disease, Tropical Sprue
- Non Specific Malabsorbtion Syndromes
- Neonatal NEC
- Small bowel overgrowth – anastomoses Fistulae, blind loop
- D. latum, Giardia, Strongyloides stercoralis
- Defective Transport
- Congenital TC II defect
- Transient TC II deficiency
- Partial R-binder defect
- Defects in B12 metabolism
- Adenosyl cobalamine deficiency CblA & CblB diseases
- Methylcobalamine deficiency Cbl E &Cbl G
- Combied Methyl and adenosyl Cll Deficienct – Cbl C, Cbl D, Cbl F
- Methyl malonyl CoA mutase defect
- Liver disease
- Drugs – impaired absorbtion/utilization: PAS, colchicine, Neomycin, ethanol, OC pills, Metormin
Causes of FA deficiency
- Inadequate intake
- Poor diet
- Poor cooking practices
- Defective absorption
- Goat’s milk
- Heat sterilized food in post BMT
- PKU, MSUD
- Defective Absorption
- Congenital isolated folate malabsorbtion
- Idiopathic steatorrhea
- Tropical sprue
- Total/Partial gastrectomy
- Diverticula of small intestine
- Jejunal resection
- Regional ileitis
- Whipples disease
- Lymphoma of intestine
- Post BMT
- OC pills
- Dietary: glyceine, methionine
- Increased Requirements
- Rapid growth ex prematurity
- Chronic hemolytic anemia
- Dyserythropoietic anemias
- Malignancy – leukemia , lymphoma
- Hypermetabolic states – infection, Hyperthyroidism
- Post BMT
- Folate metabolism defects
- Congenital deficiencies of
- Glutamate formiminotransferase
- Functional/primary N5Methyl THF homocysteine transferase
- Dihydrofolate reductase
- Methyl-THF cyclohydrolase
- FA antagonists – MTX, TMP, pyrimethamine, pentamidine
- Cbl deficiency
- Liver disease
- Increased Excretion
- Cbl def
- Liver and heart disease
- APPROACH TO DIAGNOSIS
||Mean Corpuscular Volume (fl)
| 1 wk
|3 to 6 mo
|0.5 to 2.0 yr
|2 to 6 yr
|6 to 12 yr
|12 to 18 yr
|18 to 49 yr
- PERIPHERAL SMEAR
- BONE MARROW ASPIRATE
FALSELY RAISED CBL LEVELS IN THE PRESENCE OF A TRUE DEFICIENCY
- Cbl binders (TC I and II) increased (myeloproliferative states, hepatomas, and fibrolamellar hepatic tumors)
- TC II-producing macrophages are activated (autoimmune diseases, monoblastic leukemias, and lymphomas)
- Release of Cbl from hepatocytes (active liver disease)
- % saturation of TC II – Technical issues and validation failure
- Urinary MMA test - inadequate clinical data, Renal dysfunction and dehydration factors, on the kinetics of reduction of urinary MMA to Cbl replacement
- Deoxyuridine suppression test : not widely available
- B12 absorption-levels after oral b12
- Urinary excretion using cobalt 58-accurate urine measurement, b12/folic acid deficiency leads to decreased renal absorption
- B12 binding capacity-plasma transcobalamine measurement
- Holo TC- first to diminish
Parenteral vs oral maintenance in patients with malabsorption
- Advantages in ease, cost, and comfort,
- Possible disadvantages of dosing with meals.
- Relapse in patients with IF-related malabsorption occurs within 1 to 2 years.
- MMAor homocysteine is a better monitoring tool than serum cobalamin and provides early warning of relapse if measured annually.
RECOMMENDED DAILY ALLOWANCE
Sources of Cbl (VIT B12)
- Cbl is only produced in nature by Cbl-producing microorganisms.
- Humans - solely from diet.
- Herbivores - from plants contaminated with Cbl-producing bacteria that grow in roots and nodules of legumes.
- Exogenous contamination of plants by feces
- Carnivores - Cbl supply by ingesting tissues.
- Cbl is produced by bacteria in the large bowel of humans - too distal for absoption
- Food Cbl is stable to high-temperature cooking processes
- Converted to inactive analogues by ascorbic acid.
- Animal protein is the major dietary Cbl source.
- Meats from parenchymal organs are richest in Cbl > fish and animal muscle, milk products egg yolk
- Of the total body content of 25 mg in adults, 1 mg is in the liver.
- There is an obligatory loss of 0.1% per day regardless of total body Cbl content.
- It takes 34 years to deplete stores if abruptly stopped
- Longer in V/O enterohepatic circulation
Sources of Folic Acid
- Leafy vegetables (spinach, lettuce, broccoli, beans)
- Fruits (bananas, melons, lemons)
- Yeast, mushrooms,
- Animal protein (liver, kidney)
- Human breast milk
- Pasteurized cow's milk.
- Infant formulas
- Goat's milk / powdered milk is deficient
- Increased vitamin requirements - pregnancy, growth in infancy, chronic hemolysis.
- The normal infant daily requirement is 25–35 µg/day.
- The requirements on a weight basis are higher in children than adults, - increased needs of growth
- Extremely thermolabile
- Prolonged cooking (for >15 minutes)
- In large quantities of water
- Absence of reducing agents
- Oxidation of food folate by nitrites reduces its bioavailability.
- Pteroylpolyglutamates - absorbed less efficiently than pteroylmonoglutamate
- Foods (cabbage, lettuce, orange) are not well absorbed
- Other dietary folates are nutritionally available
- Enterohepatic circulation
RARE CAUSES – INBORN ERRORS
Deficiency of Intrinsic Factor
- Appears after the first year but before the fifth year of life
- Ormal gastric acid secretion and normal findings on gastric cytologic examination
- No detectable intrinsic factor is produced
- Immunologically reactive but nonfunctional intrinsic factor
- Reduced affinity for cubam, reduced affinity for cobalamin
- Failure to thrive, recurrent gastrointestinal or respiratory infections, pallor, and fatigue.
- Megaloblastic anemia is usually present. Neurologic signs may be relatively mild
- Proteinuria that is neither of the classic glomerular or tubular type
- Deficiency of the intrinsic factor–cobalamin receptor complex, cubam.
- The proteinuria is a result of disruption of cubam function in the proximal tubule of the kidney
- Treatment involves intramuscular injection of cobalamin, initially at 1 mg OHCbl daily for 10 days, followed by monthly injection afterward.
- At a much earlier age than in patients with other causes of cobalamin malabsorption, usually in the first months of life
- Severe immunologic deficiency with defective cellular and humoral immunity
- Mutations in the TCN2
- Serum cobalamin levels must be kept very high if transcobalamin-deficient patients are to be treated successfully. Levels ranging from 1000 to 10,000 pg/mL have been required and are achieved with doses of oral OHCbl or CNCbl twice weekly (500 to 1000 μg) or with systemic administration of CNCbl or OHCbl (1000 μg) weekly or more often.
Haptocorrin (R Binder, Transcobalamin I or III) Deficiency
- Deficiency or complete absence of haptocorrin in plasma, saliva, and leukocytes
- Although serum cobalamin levels are low, holo-TC levels are normal and the patients are not clinically deficient in cobalamin
- Optic atrophy, ataxia, long tract signs, and dementia
- Haptocorrin may play a role in the scavenging of cobalamin analogues that may be toxic to the brain
Inborn Errors of Cobalamin Metabolism
- Homocystinuria, methylmalonic aciduria, or both, depending on whether synthesis of MeCbl, AdoCbl, or both cobalamin cofactors
- Only disorders in which synthesis of MeCbl is impaired, either alone (cblE, cblG, cblD variant 1) or in combination with AdoCbl synthesis (cblC, cblD, cblF), are characterized by megaloblastic anemia.
- The diagnosis of inborn errors of cobalamin metabolism is usually carried out with the use of cultured fibroblasts
- Molecular diagnosis
- Prenatal diagnosis by biochemical analysis of cultured amniocytes or chorionic villus cells has been sought for most of the classes of inborn errors of cobalamin metabolism
- Analysis of amniocytes appears to be more reliable than that of chorionic villus cells. In addition, gas chromatography–mass spectroscopy or liquid chromatography–tandem mass spectroscopy has been used to detect the presence of methylmalonic acid or homocysteine in amniotic fluid.
Functional Methionine Synthase Deficiency
- Functional methionine synthase deficiency is characterized by elevated plasma homocysteine, homocystinuria, and hypomethioninemia without methylmalonic aciduria.
- Two distinct groups of patients have been identified: cblE and cblG.
- The clinical and biochemical findings in the two disorders are virtually identical.
- Patients are usually seen initially in the first 2 years of life, but some have not been symptomatic until adulthood. The most common findings in both cblE and cblG disease include megaloblastic anemia and various neurologic problems, including developmental delay and cerebral atrophy.
- Other findings include electroencephalographic abnormalities, nystagmus, hypotonia, hypertonia, seizures, blindness, and ataxia. Findings in patients with adult onset of symptoms have typically involved neurologic or psychiatric symptoms.
- Fibroblasts from both cblE and cblG patients show decreased synthesis of MeCbl and decreased activity of methionine synthase in the presence of normal AdoCbl synthesis and methylmalonyl-CoA mutase activity]
GLUCOSE-6-PHOSPHATE DEHYDROGENASE DEFICIENCY
Glucose-6-Phosphate Dehydrogenase Deficiency commonly known as G-6-PD deficiency is common in the malaria belts. It manifests as a hemolytic anemia in children when anti malarial drugs are given. The child is usually diagnosed when investigation of hemolytic anemia is done occurring in some individuals treated for malaria with 6-methoxy-8-aminoquinoline drugs.
Biochemical pathways through which red cells metabolize sugar were painstakingly unraveled by Warburg, Embden, and Meyerhof and were the result of tests performed on prisoner volunteers serving sentences in various prisons.
THE MECHANISM OF HEMOLYSIS
The hemolytic process is the inability of the erythrocytes to protect sulfhydryl groups against oxidative damage. There is targeted disruption of the gene encoding leading to hemolysis (breakdown of Red Blood Cells). On microscopic examination there is appearance of Heinz bodies both in vivo and in vitro in G6PD-deficient cells and their inability to protect their GSH against drug challenge. Glutathione peroxidase has little effect on oxidation of hemoglobin of murine cells challenged with peroxides.
DRUGS AND CHEMICALS TO BE AVOIDED BY PERSONS WITH G6PD DEFICIENCY
- Diaminodiphenyl sulfone
- Furazolidone (Furoxone)
- Henna (Lawsone)
- Isobutyl nitrite
- Methylene Blue
- Niridazole (Ambilhar)
- Nitrofurantoin (Furadantin)
- Phenazopyridine (Pyridium)
- Urate oxidase