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TRANSCRIPT
Ghulam Abbas
BSc MBBS MSc (Sports Med)MRCS FRCS (Tr & Orth) PGHE
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Introduction
Basic Genetics
Research Evidence
Summary
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Marrying first cousin increases the risk ofchildren having genetic disorders pretermbirth and early death
Many people are unaware of this, orunderestimate the impact of the risks
The risk is up to 2 % in unrelated parents
Chance at least doubles if you marry your
first cousin
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Observation in the family or community
Historical facts – A royal pain in the genes
Published data
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Grew up in a small village
Left village in 1988
Medical camp 2009
Recognised children's tribes
looking at them, kept “pure”
Similar birth defects
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Reflection in plane journey
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Rejecting labor-savingtechnologies
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Religious persecutions
Large families are a blessing from God
Descend from about 200 founders
Higher incidences of genetic disorders
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Extinction of Habsburg Dynasty (1516–1700)
Marrying cousins or other blood relatives wasprevalent
The last king was Charles II
impotence/infertility
Alvarez et al 2009
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G×Einteraction
Health
Genetics
Environment
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1. Segregation
2. Dominance
3. Independentassortment
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A normal cell has two variants for a trait.
An egg or a sperm contains one variant randomly chosenfrom the two variants in each cell
If you have one variant for brown eyes (B) and one variantfor blue eyes (b) then each cell of your body will have Bband each egg or sperm will carry one of B or b chosenrandomly
B b
B BB Bb
b Bb bb
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Eggs
Sperm
If your two variants are different such as Bb, the traitassociated with only one of these will be visible (dominant)while the other will be hidden (recessive). For example B isdominant, b is recessive.
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B b
B BB Bb
b Bb bbEggs
Sperm
State of the two variants Observed characteristics
BB (both for brown eyes) Brown eyes
Bb (one for brown eyes, one for blue eyes) Brown eyes
bb (both for blue eyes) Blue eyes
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Simplified view of eye colour inheritance:
Brown dominant: BB, Bb
Blue recessive: bb
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Human eye colour
B b
B BB Bb
b Bb bbEggs
Sperm
Increase the likelihood of inheriting the samegenes from both parents
Gene diversity declines as compared torandom mating populations
Inheriting the same genes from both parentsincreases recessive diseases
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All papers published in English between April1, 1965, and April 1, 2013.
search terms
“congenital abnormalities/epidemiology”AND “consanguinity.”
cousin marriage / birth defects
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Identified 219 relevant scientific papers
28 papers primary data related to cousinmarriages
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Exclusion criteria Inclusion criteria
Studies with smallsize
Observational and nocontrol group
no corrections forother risk factors
Contemporary controlgroups
Blood related vUnrelated union
Su cient size toachieve statisticalsignificance
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13,776 pregnancies
Congenital anomalies 6.1 % (cousinmarriage) v 2.1% (non-cousin marriage)
Microcephaly and Congenital heart disease
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L. Charafeddine et al, 26 hospitals inLebanon
Paediatric and Perinatal Epidemiology, 2012,
65,402 births studies
1.8 fold increase in death rate beforedischarge in cousin marriage V non-cousinmarriage
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1.56 million births in Norway from 1967 to1993
Compared three groups (Both parents native,one native and first cousins)
Relative risk of congenital anomalies twice inchildren whose parents were first cousins
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Mumtaz et al, Am J Epidemiol 2010
39,745 livebirths
19 hospitals in Lebanon
1.6-fold net increased risk - infants of cousinmarriage
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Four Hospitals , Jerusalem
561 Arab newborns
Incidence of major congenital malformations
8.7% first cousin couples
7.1% all consanguineous couples
2.6% non-consanguineous couples
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There is a link between cousin marriage andbirth defects, preterm birth and early death
Risk between 2 to 4 times depending uponthe study and type of genetic disorder
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