Tapeshwar Yadav (Lecturer)

BMLT, DNHE, M.Sc. Medical Biochemistry

INBORN ERRORS OF METABOLISM

Garrod coined the term `INBORN ERRORS OF METABOLISM`

An inherited enzyme deficiency leading to the disruption of normal bodily metabolism.

Accumulation of a toxic substrate. Impaired formation of a product normally

produced by the deficient enzyme.

Garrod`s hypothesis :-

A B C

Dsubstrate excess product deficiency

toxic metabolite

Small molecule diseaseCarbohydrateProteinLipidNucleic Acids

Organelle disease

LysosomesMitochondriaPeroxisomesCytoplasm

Prenatal DiagnosisNewborn ScreeningLater life diagnosis

Prenatal Diagnosis

Index of suspicionFamily History

Have a child already affected by an inherited disorder.

One of the parents affected by autosomal or X-linked disorder.

H/O Neonatal deaths, fetal lossesMaternal family history

males - X-linked disorders all - mitochondrial DNA is maternally

inheritedA positive family history may be helpful!

Enzymatic assay of cultured amniocytesChorionic villi sampling to determine the

chromosomal,enzymatic or molecular genetic status of the fetus.

CytogeneticsEnzyme assay.

Newborn Screening

Reliable screen test and low false negative results.

Test is simple and inexpensive Available results soon to start effective

therapyDefinite follow up testOutcome without treatment is very badEffective therapy is available

Index of suspicion

“with any full-term infant who has no antecedent maternal fever or PROM (premature rupture of the membranes) and who is sick enough to warrant a blood culture or LP, one should proceed with a family history & few simple lab tests.

Family HistoryMost IEM’s are recessive - a negative family

history is not reassuring!Consanguinity, ethnicity, inbreedingneonatal deaths, fetal lossesmaternal family history

males - X-linked disorders all - mitochondrial DNA is maternally

inheritedA positive family history may be helpful!

Simple laboratory tests

Glucose, Electrolytes, Gases, Ketones, BUN Creatinine

Lactate, Ammonia, Bilirubin, LFTAmino acids, Organic acids, Reducing

subst.

Specialized biochemical testingAmino acid analysis

Maple syrup urine disease with increase leucine, valine and isoleucine

Hyperglycinemia: increase glycineOrganic acid : propionic acidemiaCarnitine levelChromatography of glycolipidIncreased level of long chain fatty acid

with perioxisomal disorder

Carbohydrate metabolism

GalactosemiaGalactosemia Enzyme deficiency:- Galactose-1-p uridyl transferase Galactokinase Uridine diphosphate galactose 4

epimeraseScreening :- Failure to thrive Hypoglycemia Urine demonstrates the presence of

reducing substance that does not react to glucose oxidase.

Galactose can be identified by chromatography.

Galactose & galactose-1-p in bloodConfirmed :- Assaying red blood cell transferase activity.

Fructosuriaa Enzyme deficiency:- • Essential Fructosuria - Fructokinase• Inherited Fructose Intolerance - Fructose-1-P aldolase• Hereditary fructose-1,6-diphosphatase deficiency Screening :- • Fructosuria after eating fructose containing food• Hypoglycemia Confirmed :-

• Enzyme defect in liver biopsy.

Hemolytic diseases

Enzyme deficiency:- Pyruvate kinase Glucose-6-phosphate

dehydrogenase Screening :- Lactic acidosis on glucose load

Hemolytic anemia Confirmed :- Specific enzyme activity.

Glycogen Storage DisordersGlycogen Storage Disorders Type 1-Von Gierke’s Enzyme deficiency:- Glucose-6-phosphatase Screening :-

Life threatening Hypoglycemia Lactic acidosis Hyper-uricemia Hyper lipidemiaAdverse response to Glucagon with worsening Lactic

acidosis.Confirmed :- Glucose-6-phosphatase enzyme

activity assay in liver biopsy.

Enzyme deficiency:-

Type 2- Pompe’s disease- Acid α-glucosidase Type 3- Deficency of Glycogen debranching enzyme Type 4- Deficiency of Branching enzyme Type 5- McArdle`s Syndrome- Muscle phosphorylase Type 6- Liver phosphorylase or phosphorylase kinase

Screening :- Almost same as type I

Confirmed :- Respective enzyme activity assay in liver & muscle biopsy.

MucopolysacccharidosisMutation in a gene encoding a lysosomal hydrolase involved in the degradation of 1 or more GAGs

Defective lysosomal hydrolase

Accumulation of substates in various tissues including Liver,spleen,skin,bone & CNS

Hurler syndrome – α l-iduronidaseHunter syndrome - iduronate sulfatase

• Urinalysis for presence of ↑ GAGs• Assay of suspected enzymes in WBC,fibroblast or serum• Tissue biopsy with subsequent analysis of GAG by electrophoresis• Use of specific gene test• Prenatal diagnosis by amniotic fluid cells or chorionic villus sampling.

Amino acid metabolism

Aromatic Amino acid metabolism Phenylketonuria Enzyme deficiency:- Phenylalanine hydroxylase Dihydrobiopterine reductase 6-Pyruvoyl-tetrahydropterin synthase GTP cyclohydrolase I Pterin-4-carbinolamine dehydratase Screening :- FeCl₃ to detect urinary phenyl pyruvate Tandem mass spectrometry. Prenatal Diagnosis :- DNA probe Confirmed :- Elevated blood phenylalanine level. Enzyme activity

Tyrosinemia Enzyme deficiency:- Type I- Fumarylacetoacetase Type II-Tyrosine aminotransferase Type III-4-hydroxyphenylpyruvate dioxygenase Screening :- FeCl₃ Tandem mass spectrometry. Prenatal Diagnosis :- RFLP Confirmed :- Elevated conc of tyrosine in plasma Succinyllactone in urine,by product of fumaryl

acetoacetic acid in urine.

Maple syrup urine disease

Enzyme deficiency:- Branched chain ketoacid dehydrogenase complex Screening :- Acidosis Ketotic hypoglycemia Pancreatitis Odor of maple syrup Mixing urine with DNPH Prenatal Diagnosis :- DNA analysisConfirmed :- Elevated plasma level of Branched chain amino-

acids. 2hydroxy valeric acid in urine.

Enzyme deficiency:-

Hypermethioninemia- Methionine adenosyl transferase Homocystenuria - Cysthionine β-synthase Cystathionuria - Cystathionase

Prenatal Diagnosis :- DNA analysis

Confirmed :- Elevated levels of the regarding substrates in

plasma.

Urea cycle disorders N-acetylglutamate synthase – Glutamine,Alanine & Citruline CPS - Glutamine,Alanine & Citruline ,Arginine OTC –Orotic acid(U) Glutamine,Alanine & Citruline ,Arginine Arginisuccinate synthase - Citrulline,Orotic acid(U) Arginisuccinate lyase- Arginisuccinic acid (B & U) HHH syndrome – Mytochondrial ornithin transporter.

Screening :- Hyperamonimia

Prenatal Diagnosis :- DNA analysis

Disorders of heme metabolismMutation in various genes

Abnormalities of the enzymes of the heme synthesis

Accumulation of ALA& PBG ↓in heme in cell & body fluid

Nuropsychiatric signs & symtoms

Accumulation of porphyrinogen In skin & tissues

Sponteneous oxidation of Porphyrinogen to porphyrin

photosensitivity

Prenatal diagnosis - Appropriate DNA probe

Diagnosis by ↑ corproporphyrin,uroporphyrin,ALA,PBG,protoporphyrin

Metabolism of Fatty acid

Impaired oxidation of Fatty acid1) Transporter deficiency:- CPT-I & CPT-II deficiency Prenatal Diagnosis :- Enzyme assay in aminocentesis DNA analysis Confirmed :- Elevated levels of free carnitine & acyl

carnitine in plasma.

2) Dicarboxylic aciduria- medium chain acyl coa dehydrogenase deficiency

3) Refsum disease- Accumulation of phytanic acid

4) Zellweger`s syndrome- Absence of peroxisomes

Lipid storage disease Tay-Sachs disease – Hexosaminidase Fabry`s disease – α-galactosidase Metachromatic leucodystrophy- Arylsulfatase A Krabbe`s disease- β- galactosidase Goucher disease- β- glucosidase Niemann-Pick disease- Sphingomyelinase Farbe`s disease - CeramidaseDiagnosis:- Analysis of tissue sample peripheral leucocyte plasma amniotic fluid Culture fibroblast for presence of enzymatic activity or accumulated

lipidPrenatal diagnosis – DNA probe

Disorder of nucleic acid metabolism Purine metabolism:- Gout – Genetic defect in PRPP synthetase Lesch-nyhan syndrome- hypoxanthine-guanine

phosphorybosyl transferase Hypouricemia – Xanthine oxidase deficiency ADA & purine nucleoside phosphorylase

deficiency- defective T & B cell function Pyrimidine metabolism:- Hydroxy butyric aciduria- dihydropyrimidine

dehydrogenase Orotic aciduria – Orotate phosphorybosyl transferase

& orotidyl decarboxylase Diagnosis :- Assay of respective enzyme activity

Thank you !