This document discusses genetic disorders, which are caused by mutations in genes or chromosomes inherited from a person's parents. It classifies genetic disorders into single gene defects, multifactorial disorders caused by multiple genes and environment, and chromosomal/cytogenic disorders involving changes in chromosome number or structure. Examples are provided for autosomal dominant and recessive disorders, sex-linked disorders, multifactorial disorders, and chromosomal disorders including Down syndrome, Klinefelter syndrome, and Turner syndrome.

1. Genetic
Disorder
Dr. Saugat Chapagain

2. Genetic Disorder
Caused by a mutation of a gene, group of genes
or an entire chromosome.
The mutation or defect is inherited.
 Classification:
1. Single gene defect (mendelian disorder)
1. Autosomal (dominant/ recessive)
2. Sex linked (dominant/ recessive)
2. Multifactorial
3. Cytogenic or chromosomal

3.  Chromosome-
 Carrier of DNA with hereditary information.
 Normal somatic cell contains 46 chromosomes
 2x 23 pairs
 22 pairs autosomes and 1 pair sex chromosomes.
 Male – XY
 Female – XX
 Gene-
 Unit of inheritance of character.
 Mutation-
 Permanent change in the DNA

4. Mendelian disorder
 Unifactorial inheritance
 Defect in a single gene of large visible effect.
 Dominant -
o Manifested even on a heterozygote
 Recessive –
o Manifested only if homozygous.
 Autosomal –
o Affects both male and females equally
 Sex linked / X linked –
o May affect either depending on the gene linked.
o Almost always X-linked and affects male.

9. 1. Autosomal dominant:
 Familial hypercholesterolemia
 Polycystic Kidney Disease
 Hereditary spherocytosis
 Von Willebrand’s disease
2. Autosomal recessive:
 Thalassaemia
 Sickle cell anaemia
 Cystic fibrosis
 Alpha 1 antitrypsin deficiency
 Glycogen storage disorder
 Neurogenic muscular
atrophies
 Spinal muscular atrophy
 Congenital adrenal
hyperplasia.
3. X-linked recessive
 Haemophilia A
 Haemophilia B (X-mas
disease)
 G6PD deficiency
 Nephrogenic diabetes
insipidus
4. X-linked dominant
 Vitamin D resistant rickets.
Examples

10. Multifactorial disorders
 Polygenic inheritance
 2 or more genes + environmental factors
 Examples –
 Congenital heart diseases
 Coronary heart diseases
 Essential hypertention
 Diabetes mellitus
 Cleft palate or lip
 Pyronic stenosis

11. Cytogenic/ chromosomal
disorders
 Aberrations in the number or structure of chromosomes.
 Haploid / polyploidy (69XX, 92XX)
 Aneuploidy (47XXY)
 Autosomal disorders:
 Trisomy 21/ Down’s Syndrome
 Trisomy 18/ Edward’s Syndrome
 Trisomy 13/ Patau’s syndrome
 Cri du Chat syndrome (missing part of 5th chromosome)
 Sex chromosomal disorders:
 Klinefelter’s syndrome (47XXY)
 Turner’s syndrome (45 XO)
 Triple X syndrome (47 XXX)
 47 XYY – has normal phenotype

12. Patau’s Down’s

15. Klinefelter’s Syndrome

16. Turner’s Syndrome

17. 47 XXX