(2) 1.genetic disorders & inborn errors of metabolism
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7/29/2019 (2) 1.Genetic Disorders & Inborn Errors of Metabolism
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GeneticGenetic
Disorders & Disorders &
Inborn ErrorsInborn Errorsof Metabolismof Metabolismpd f Mach ine - i s a pdf w r i te r t ha t pr oduces qua l i ty PDF f i l es w i t h ease!
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Categories of GeneticCategories of Genetic
DisordersDisorders
1.1. Chromosomal disordersChromosomal disorders
2.2. Monogenic disordersMonogenic disorders3.3. MultifactorialMultifactorial disordersdisorders
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Categories of GeneticCategories of Genetic
DisordersDisorders1.1. Chromosomal disordersChromosomal disorders – –
Includes conditions in which there isIncludes conditions in which there is
excess loss of chromosomes, deletion of aexcess loss of chromosomes, deletion of apart of chromosome or translocationpart of chromosome or translocation
Can be recognized by analysis of theCan be recognized by analysis of the
karyotypekaryotype (chromosomal pattern) of an(chromosomal pattern) of an
individualindividual
E.g.E.g. TrisomyTrisomy 21 (Down21 (Down’ ’ s Syndrome)s Syndrome)
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Categories of GeneticCategories of Genetic
DisordersDisorders
2.2. Monogenic disordersMonogenic disorders – –
Involves single mutant geneInvolves single mutant gene Classified asClassified as – –
a.a. Autosomal Autosomal dominantdominant
b.b. Autosomal Autosomal recessiverecessivec.c. XX--linkedlinked
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Categories of GeneticCategories of Genetic
DisordersDisorders
3.3. MultifactorialMultifactorial disordersdisorders – –
Involves no. of genesInvolves no. of genes Pattern of inheritance of thesePattern of inheritance of these
conditions does not conform toconditions does not conform to
classicclassic MendelianMendelian genetic principlegenetic principle
E.g. common adult diseases like IHDE.g. common adult diseases like IHD
& HT& HT
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Inborn Errors of Inborn Errors of
MetabolismMetabolism – – A Definition A Definition ‘ ‘ A mutation in a structural gene may affect the A mutation in a structural gene may affect the
structure of the encoded protein. If anstructure of the encoded protein. If an
enzyme is affected anenzyme is affected an inborn error of inborn error of metabolismmetabolism may resultmay result’ ’
‘ ‘Inborn Error of MetabolismInborn Error of Metabolism is a geneticis a genetic
disorder in which a specific enzyme isdisorder in which a specific enzyme isaffected, producing a metabolic block, whichaffected, producing a metabolic block, whichmay have pathological consequences.may have pathological consequences.’ ’ E.g.E.g.PKU,PKU, CystinuriaCystinuria,, PentosuriaPentosuria, Albinism etc., Albinism etc.
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Patterns of InheritancePatterns of Inheritance Inheritance characteristics of an individual are determined by aInheritance characteristics of an individual are determined by aboutbout
50,000 gene pairs arranged on 23 pairs of chromosomes, one of 50,000 gene pairs arranged on 23 pairs of chromosomes, one of each pair coming from father & one from mother.each pair coming from father & one from mother.
Out of 23 pairs of chromosomesOut of 23 pairs of chromosomes
22 pairs determine 1 pair deter22 pairs determine 1 pair determinesmines
characteristics of sex of ancharacteristics of sex of an individualindividual
body cellsbody cells
Autosomes Autosomes Sex ChromosomesSex Chromosomes (X & Y)(X & Y)
Chromosome of each Female has 2X chromosoChromosome of each Female has 2X chromosomes (XX)mes (XX)
autosomeautosome pair are & male have one X & onepair are & male have one X & one Y Y
homologoushomologous
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Patterns of InheritancePatterns of InheritanceDuring development of male & female reproductive cellsDuring development of male & female reproductive cells
Meiosis occursMeiosis occurs
SpermSperm OvumOvum
2222 Autosomes Autosomes + 22+ 22 Autosomes Autosomes ++
X or Y chromosomeX or Y chromosome X chromosomeX chromosome
FertilizationFertilization
Diploid Cell (46 chromosomes)Diploid Cell (46 chromosomes)
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Autosomal Autosomal DisordersDisorders
‘ ‘If an inherited disease is caused by aIf an inherited disease is caused by a
mutant (abnormal) gene situated onmutant (abnormal) gene situated on
anan autosomeautosome, the disorder is called, the disorder is called
autosomalautosomal’ ’
It may be dominant or recessiveIt may be dominant or recessive
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1.1. Autosomal Autosomal DominantDominant
DisorderDisorder
Presence of one mutant gene isPresence of one mutant gene is
necessary for the trait to benecessary for the trait to be
manifested in the carrier.manifested in the carrier.
E.g.E.g. HbpathiesHbpathies like SCA like SCA
HereditaryHereditary spherocytosisspherocytosis & &
Acute Acute intermittantintermittant porphyriaporphyria
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1.1. Autosomal Autosomal DominantDominant
DisorderDisorder
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2.2. Autosomal Autosomal RecessiveRecessive
DisorderDisorder
Disease is manifested only inDisease is manifested only in
homozygous (presence of 2 mutanthomozygous (presence of 2 mutant
genes)genes)
E.g. Cystic fibrosisE.g. Cystic fibrosis
PKUPKU
GalactosemiaGalactosemia
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1.1. Autosomal Autosomal RecessiveRecessive
DisorderDisorder
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Sex Linked DisorderSex Linked Disorder Most of the sexMost of the sex--linked disorders are carried on Xlinked disorders are carried on X--
chrchr
Females have 2 XFemales have 2 X
--chrchr
but only one of them is activebut only one of them is active
A women with one X A women with one X--chrchr carrying a recessivecarrying a recessivedisorder is unaffected clinically (Carrier)disorder is unaffected clinically (Carrier)
Homozygous female will however show the disorderHomozygous female will however show the disorder
Males have only one XMales have only one X--chrchr & this is always active. A & this is always active. A
male carrying recessive gene is therefore alwaysmale carrying recessive gene is therefore alwaysaffected clinicallyaffected clinically
E.g. GE.g. G--66--PD deficiency, Hemophilia, etc.PD deficiency, Hemophilia, etc.
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Sex Linked DisorderSex Linked Disorder
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Clinical Importance of Clinical Importance of
Inborn Errors of MetabolismInborn Errors of Metabolism DiagnosisDiagnosis
Prevent these conditions by geneticPrevent these conditions by genetic
counselingcounseling Prenatal diagnosis during subsequentPrenatal diagnosis during subsequent
pregnancies can help terminate thepregnancies can help terminate thepregnancy or plan apt place & plan forpregnancy or plan apt place & plan fordeliverydelivery
Recognition in early infancy of diseases likeRecognition in early infancy of diseases likeGalactosemiaGalactosemia, PKU, MSUD may prevent, PKU, MSUD may preventirreversible clinical consequences or deathirreversible clinical consequences or death
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Clinical Importance of Clinical Importance of
Inborn Errors of MetabolismInborn Errors of Metabolism Blood relatives of affected patients shouldBlood relatives of affected patients should
screen themselves for Gscreen themselves for G--66--PD deficiency,PD deficiency,Familial hypercholesterolemia,Familial hypercholesterolemia, cystinuriacystinuria,,WilsonWilson’ ’ s diseases disease
Following inherited disorders can beFollowing inherited disorders can betreated symptomaticallytreated symptomatically – – congenitalcongenitaldisaccharidasedisaccharidase deficiency, hereditarydeficiency, hereditarynephrogenicnephrogenic diabetesdiabetes insipidusinsipidus
Following inborn errors are almostFollowing inborn errors are almostcompletely harmlesscompletely harmless – – renalrenal glycosuriaglycosuria,,GilbertGilbert’ ’ s diseases disease
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