Presentation on theme: "Dr. Muhammad Rafique Assist. Prof. Paediatrics College of Medicine K K U Abha K S A."— Presentation transcript:
Dr. Muhammad Rafique Assist. Prof. Paediatrics College of Medicine K K U Abha K S A
Human Genetics Introduction: Genetic diseases common cause of diseases, death and prolonged handicap. 1% newborns monogenic diseases like CF,SCD etc. 0.5% chromosomal disorders like Down Syndrome. 1-3% multifactorial disorders like CHD, spina bifida. 40% deaths due to genetic disorders& birth defects.
Modes of Genetic Inheritance
Mode of inheritance Mendelian Polygenic multifactoriaL l Non traditional AD AR XD XR Y-linked Imprinting disorders Triple repeat expansion Mitochondrial Chromosomal Numerical Structural
MENDELIAN INERITENCE Classically 4 forms of genetic inheritance..Autosomal dominant (A D ).Autosomal recessive (A R ).X-linked recessive..X-linked dominant -Foundation of single gene inheritance. -Single gene sufficient to impact phenotype.
AUTOSOMAL DOMINENT Either parent can transmit to 50% offspring. Same family show variable expressivity. Male /female equally affected. Vertical transmission-(parents to offspring). Involve all generations (no skip generation). No carrier state.
MUTATION Spontaneous change in genetic material 1-Gain function mutation; over/inappropriate expression of a gene product. Mostly produce AD disorder e. g. achondroplasia. 2-Loss of function mutation; observed in A R disorders.50% enzyme activity in hetro- normal function e.g.(SCD)
AUTOSOMAL RECESSIVE Both parents are clinically normal but carrier. Both M&F but homozygous are affected. 25% offspring pt.,25% normal,50% carrier risk. If a pt. marries a normal person,all kids carrier. Mostly conditions are enzyme defects& IEM. Less variability among affected persons. Consanguinity increases its risk.
X-LINKED RECESSIVE INHERITENCE Males are affected. Females – carrier, normal/only mild s/sympt. Males daughters,100% carrier,(XY). All sons normal(no male to male transmission) Carrier females sons 50 % norml,50 % pts(XX). Carrier mothers 50% daughters normal (XX).
X-LINKED RECESSIVE DISORDERS Duchene muscular dystrophy. Haemophelia A & B. Nephrogenic diabetes insipidus. G6-PD deficiency. Colour blindness.
X-LINKED DOMINANT INHERIT. Can manifest in heterozygous female. In female twice common (XX). Manifestations more variable in females. 50% risk for both f/m offspring of hetro. F. All daughters of pt. father are affected(XY). Example-Vit. D resistant ricket - Pseudo-hypo-parathyroidism -X-linked hypophosphatemic rickets
Y-LINKED INHERITANCE There are only few Y- linked traits. Male to male transmission only. Most Y–linked genes are related to sex determination & reproduction and are associated with infertility. Rare familial transmission of Y-linked disorders.
Polygenic/multifactorial Inheritence Combination of geneti+environmental factors. General population incidence 1-1.5/1000. Recurrence risk (2 nd time)for kid/sibling 3-5%. Re-recurrence risk(3 rd time) about 8-10%. Risk/severity increas with more pts. relatives. CDH is F>M while pyloric stenosis is M>F. Recurrence risk cleft lip+palat> only cleft lip.
Mitochondrial Inheritance A woman with a mitochondrial genetic disorder will have affected offspring of either sex. An affected father will have no affected offspring.
Mitochondrial Inheritance Diseased Normal
CURRRENT UNDERSTANDING OF GENETICS OF COMMON DISORDERS Impact of genetics in paediatrics diseases is being realized. Prevention and intervention may soon be possible in,at risk children. Examples;.Type 1 diabetes mellitus..Early onset childhood obesity.Asthma
Type 1 Diabetes Mellitus Polygenic multi-factorial paediatric illness. In affected families many loci appears to be linked to increase risk. A few gene variants confer risk for disease. Some environmental factors like viral illness. Heritability estimates about 66-72%. Twins concordance 30-50%.
T1DM-----cont---- Relative risk in general population --0.4%. Pt.s siblings has 15 times more risk (6%). Many studies indicate locus of gene on 6p21. 30% pts. have association with HLA-DQ2/DQ8.
CHILDHOOD OBESITY It is a multi-factorial disease. Many contributing factors still unknown like.Modern environment of plentiful calories..Low physical activity..With combination of gene resultobesity. Many studies suggest rare gene, acting as recessive.
CHILDHOOD OBESITY –CONT.-- Example is MC4R (melanocortin 4 receptor), found in 3% obese children. Families and twin studies estimate 50% heritability. 100 genetic associations with obesity reported in positional and functional candidates.
CHILDHOOD ASTHMA Asthma and atopy are heritable. Asthmatic parents have 60% increase risk of atopy in their kids. 3-6years children have double risk if both parents are asthmatic. Twin studies found heritability about 80%. Higher concordance in monozygotic twins.
CHILDHOOD ASTHMA– CONT.-- Children of asthmatic mother have more risk to develop asthma than asthmatic father. Some environmental factors involved are : endotoxin, cockroach, dust-mite antigens, and diesel particles. Implicated genes are found on 5q,6p,13q and 20p13.