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Introduction to Medical Genetics

Introduction to Medical Genetics. Fadel A. Sharif. Contact details. Medical Technology Department Genetics lab fsharif@iugaza.edu. Textbook: Genetics in Medicine, 7 th edition. Nussbaum, McInnes & Willard. W.B. Saunders Co. (2007). Reference

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Introduction to Medical Genetics

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  1. Introduction to Medical Genetics Fadel A. Sharif

  2. Contact details • Medical Technology Department • Genetics lab • fsharif@iugaza.edu

  3. Textbook: • Genetics in Medicine, 7th edition. Nussbaum, McInnes & Willard. W.B. Saunders Co. (2007). • Reference • Emery’s Elements of Medical Genetics, 13th edition, Turnpenny & Ellard. Churchill Livingstone. (2007).

  4. Grades • Midterm exam 30% • Assignments, participation & quizzes 10% • Final exam 60%

  5. Topics • 1: Introduction • 2: Patterns of Single-Gene Inheritance • 3: Genetic Variation in Individuals • 4: Genetic Variation in Populations • 5: Gene Mapping • 6: Principles of Clinical Cytogenetics • 7: Clinical Cytogenetics: Disorders of the Autosomes and the Sex Chromosomes • 8: Treatment of Genetic Diseases • 9: Genetics and Cancer • 10: Prenatal Diagnosis

  6. Glossary & Definitions • Genetics is concerned with variation and heredity in all living organisms • Human genetics is the science of variation and heredity in humans • Medical genetics deals with human genetic variation of significance in medical practice and research • Cytogenetics: the study of chromosomes

  7. Glossary & Definitions • Genomics: the study of genome, its organization and functions • Population genetics: genetic variation in human populations and factors that affect allele frequencies • Clinical genetics: application of genetics to diagnosis and patient care • Genetic counseling: risk information, psychological and educational support to patients and/or their families

  8. Glossary & Definitions • Genotype - the genetic constitution of the organism • Phenotype - the observable expression of genotype

  9. Glossary & Definitions • Locus - a chromosomal location • Alleles - alternative forms of the same locus • Mutation - a change in the genetic material, usually rare and pathological • Polymorphism - a change in the genetic material, usually common and not necessarily pathological

  10. Glossary and Definitions • Homozygote- an organism with two identical alleles • Heterozygote- an organism with two different alleles • Hemizygote-having only one copy of a gene • Males are hemizygous for most genes on the sex chromosomes

  11. Glossary and Definitions • Dominant trait- a trait that shows in a heterozygote • Recessive trait- a trait that is hidden in a heterozygote

  12. Family history is important • It can be critical in diagnosis • Can provide info about natural history of the disease & variation in its expression • Can clarify pattern of inheritance • Note: Diagnosis of a hereditary condition allows risk estimation in other family members so that proper management, prevention, & counseling can be offered to patient & family

  13. Role of Genes in Human Disease • Most diseases / phenotypes result from the interaction between genes and the environment • Some phenotypes are primarily genetically determined • Achondroplasia • Other phenotypes require genetic and environmental factors • Mental retardation in persons with PKU • Some phenotypes result primarily from the environment or chance • Lead poisoning

  14. Major types of genetic disease • Chromosomal disorders • Single gene disorders • Polygenic diseases

  15. Chromosomal disorders • Addition or deletion of entire chromosomes or parts of chromosomes. Rearrangement of chromosomal segments • Typically more than 1 gene involved • Classic example is trisomy 21 - Down syndrome

  16. Down Syndrome

  17. Single gene disorders • Single mutant gene has a large effect on the patient • Transmitted in a Mendelian fashion • Autosomal dominant, autosomal recessive, X-linked, Y-linked • Osteogenesis imperfecta - autosomal dominant • Sickle cell anemia - autosomal recessive • Haemophilia - X-linked

  18. Autosomal dominant pedigree

  19. Polygenic diseases • The most common yet still the least understood of human genetic diseases • Result from an interaction of multiple genes, each with a minor effect • The susceptibility alleles are common • Type I and type II diabetes, autism, multiple sclerosis

  20. Polygenic disease pedigree

  21. Identifying disease genes has been revolutionized by the sequencing of the Human Genome

  22. The sequence • 3.3 billion base pairs • Gene prediction ~ 25,000 • This is likely to be an underestimation due to the occurrence of regulatory RNAs

  23. Accessing the sequence • Public databases • Freely available • Continuously modified and updated

  24. www.ensembl.org

  25. Searching for FRZB

  26. FRZB is located on chromosome 2

  27. FRZB transcript sequence

  28. Two common amino acid substitutions in FRZB

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