Genetic Diseases & Pediatrics PDF

Introduction to genetics and pediatric diseases Lecture outline Genes, genome and chromosomes The central dogma of molecular genetics Genetics and disease Diagnosis of genetic diseases Treatment of genetic diseases Genetic testing and screening Genetic counseling ...

Introduction to genetics and pediatric diseases Lecture outline Genes, genome and chromosomes The central dogma of molecular genetics Genetics and disease Diagnosis of genetic diseases Treatment of genetic diseases Genetic testing and screening Genetic counseling  Some basic facts about genes and chromosomes Genes are located on chromosomes Chromosomes and genes are made up of DNA Genes are the blueprints of heredity. Genes are made of hundreds to thousands of DNA bases Genes work mostly by producing proteins Genes (nearly always) come in pairs Members of a pair of genes can differ from each other  The human genome 3 billion base pairs of DNA in the genome, Less than 1.5% actually encodes proteins About 5% is thought to contain regulatory elements. Only about half of the total linear length of the genome consists of so- called single-copy or unique DNA, The rest of the genome consists of several classes of repetitive DNA e.g. Alu (10%) and LINE (20%) Most (but not all) of the estimated 25,000 genes in the genome are represented in single-copy DNA, Repetitive DNA fraction contribute to maintaining chromosome structure and are an important source of variation between different individuals THE CENTRAL DOGMA of Molecular Biology DNA→RNA→PROTEIN Molecular biology’s Central “Dogma” General Special Unknown DNA → DNA RNA → DNA protein → DNA DNA → RNA RNA → RNA protein → RNA protein → RNA → protein DNA → protein protein Genetics and disease Genetic Variations, Mutations, and Human Disease Changes in genes can sometimes lead to health problems Single-gene disorders show different patterns of inheritance autosomal dominant diseases (e.g., Huntington disease) autosomal recessive diseases (e.g., sickle cell disease) X-linked diseases (e.g., Duchenne muscular dystrophy) Complex or multifactorial disorders are harder to discern (e.g., Asthma, autism, cancer, mental retardation, obesity)  Cancer Genetics and Genomics Imbalance between cellular proliferation and cellular attrition Strikes more than one third of the population, accounts for more than 20% of all deaths, and, in developed countries, is responsible for more than 10% of the total cost of medical care. Genes in which mutations cause cancer fall into two distinct categories: Oncogenes facilitate malignant transformation by stimulating proliferation or inhibiting apoptosis. Tumor-Suppressor Genes (TSGs). "gatekeepers" control cell growth regulators of various cell-cycle checkpoints mediators of programmed cell death "caretakers“ protect the integrity of the genome proteins responsible for detecting and repairing mutations proteins involved in normal chromosome disjunction during mitosis components of programmed cell death machinery What is Inheritance? Every living thing has a set of characteristics inherited from its parent or parents. Genetics is the scientific study of heredity.  Vocabulary to Know Trait: a specific characteristic varying among individuals ex: eye color Gene: a portion of DNA determining a trait; found on the chromosomes ex: the gene for eye color  Vocabulary (continued) Hybrid: the offspring of two parents with different traits Gametes: reproductive cells (aka: sex cells; sperm & egg)  Allele: the form of a gene Allele: the different forms of a gene * Represented by a letter. ex: Widow’s Peak = W * Organisms have two alleles for each trait, one inherited from the mother and one from the father. ex: WW  Forms of Alleles Dominant Allele: trait will be expressed with only one copy present * Represented with capital letters. ex: W (Widow’s peak) Recessive Allele: trait will only be expressed when no dominant alleles are present * Represented with lower case letters. ex: w (No widow’s peak)  Genes and Dominance What is a trait? A characteristic like eye color Example: Tall vs.. Short – Height  Allele Combinations Homozygous: both alleles are the same ex: WW or ww Heterozygous: alleles are different ex: Ww (capital letter is always 1st!)  Genotype: the actual allele combination; what the genes say ex: WW, Ww, ww Phenotype: the trait observed ex: Widow’s Peak  Codominance Both alleles contribute to the phenotype; neither allele is dominant. Ex: roan cattle  Multiple Alleles More than two allele possibilities. Ex: blood type  Polygenic Traits Traits controlled by more than one gene. Ex: skin color  Mendelian disorders Single gene disorders, also known as Mendelian disorders, are genetic conditions that are caused by a mutation in a single gene. Diagnosis of genetic diseases DNA-, RNA-, and protein-based diagnostics identify genetic alterations due to: Point mutations Frame-shift mutations Insertions and deletions Chromosomal aberrations: Loss, addition, translocation… Subtelomeric rearrangements Different types of tests that reveal ones genetic status Microscope-based tests Cytogenetics : Chromosomal anomalies detected by karyotyping and other tests Biochemical tests Measuring and scrutinizing actual gene products, the proteins DNA tests Some of DNA, RNA and Protein based methodologies DNA sequencing Single Nucleotide Polymorphism (SNP) PCRs Fluorescent In-situ Hybridization (FISH) Microarrays Karyotyping  Single nucleotide polymorphism (SNP) Changes at the nucleotide level it must occur in at least 1% of the population. SNPs make up 90 of variation in human genome predispose people to disease or influence their response to a drug valuable for biomedical research and for developing pharmaceutical products or medical diagnostics SNPs are also evolutionarily stable http://www.ncbi.nlm.nih.gov/Database/datamodel/  Restriction Fragment Length Polymorphism RFLP Digesting the DNA with RE Separation with gel electrophoresis Southern blotting Zewdu Terefework 2010 Microscope-based tests Cytogenetics : Chromosomal anomalies detected by Karyotyping FISH Immunohistochemical assays Zewdu Terefework 2010 Zewdu Terefework 2010  FISH Fluorescently labeled Small fragment of DNA is hybridized to specufuc region  Treatment of genetic diseases The objective in treating genetic disease is to eliminate or ameliorate the effects of the disorder, not only on the patient but also on his or her family. THE MOLECULAR TREATMENT OF DISEASE Treatment at the Level of the Protein Increase the Folding of Mutant Polypeptides Cofactor administration to increase enzyme activity Translational "skipping" over mutant stop codons Replacement of an extracellular protein Modulation of Gene Expression Pharmacological modulation of gene expression RNA interference (RNAi) Modification of the Somatic Genome by Transplantation Stem Cell Transplantation Nuclear Transplantation Therapeutic cloning Genetic screening/testing TO TEST OR NOT TO TEST  Pronatal motives and prenatal diagnosis Prenatal diagnosis is a technological system examining tissues, cells, bio- chemical products, chromosomes and DNA of a fetus Amniocentesis Chorionic villus sampling ultrasound Cytogenetics Karyotyping Enzyme analysis of cultured fetal cells Prenatal genetic tests Learn about the health problems the child face Determine the kind of medical care needed Searching for medical specialists Explore available educational and other services Finding support groups Choice of terminating pregnancy  Genetic test to determine carrier status The value of the test for future children or the extended family should be considered before taking this test Prior to having children At the point of having children After an affected child, sibling or relative is diagnosed  Genetic counselors Work as members of a healthcare team Provide information and support to families who have members with birth defects or genetic disorders Identify families at risk Investigate the problem present in the family Interpret information about the disorder Analyze inheritance patterns and risks of recurrence and review available options with the family.  Prevention of genetic diseases Genetic counseling – professional consultation – Help to determine risk – Help evaluate whether offspring have a genetic disorder – Offer advice on treatment, care Tools – Pedigree – Punnett square – karyotype  Pedigree Shows relationships in a family over several generations  Karyotype Used to find chromosomal disorders Use a sample of cells (cheek, wbc) Cells in metaphase are stained and photographed Chromosomes cut and arranged according to size  Amniocentesis Fetal cells floating in amniotic fluid are collected using a LARGE syringe  Chorionic Villus Sampling Cell from chorionic villi are collected from area surrounding embryo Cells are grown in petri dishes, then analyzed Eugenics = Beautiful inheritance Thank you