An Sci 361 1st Edition Lecture 5 Outline of Last Lecture I. Learning Goalsa. Dystrophinb. RingoII. Duchenne Muscular Dystrophy (DMD)III. Muscular Dystrophy in Golden Retrieversa. Dystrophinb. RNA Splicingc. Causesd. TreatmentsIV. Exon Skipping TherapyV. Stem Cell InjectionsOutline of Current Lecture I. Gene disordersa. Singlei. Typesii. Causesb. PolygenicII. Citrullinaemiaa. Humansi. Type Iii. Type IIb. Cattlei. CausesIII. ASS DeficiencyCurrent LectureLearning goals:• Understand the mechanisms of single-gene and polygenic traits/diseases• Learn the causes of single-gene disorders• Citrullinaemia in humans and cattle: causes, types, paper of Robinson et al.• von Willebrand disease dogsSingle Gene Disorders vs. Polygenic disorders:These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.• Single-gene disorders– Disorder caused by a mutation\alteration within one gene– The disease is caused by a mutation in a single gene– Autosomal dominant– Autosomal recessive– X-linked dominant– X-linked recessive– Y-linked– Mitochondrial• Mis-sense mutation - a single base substitution in a codon that results in an amino acid substitution• CAT is codon for histidine• CAA is codon for glutamine• Typically results in improper protein function• Non-sense mutation - a single base substitution that changes a functional codon into a stop codon• Typically results in a shortened protein• Stop codon: UGC (cysteine)  UGA– CAUSES:• Other kinds of mutations - insertions or deletions (Indels) of single or multiple bases• Can lead to frame shift mutations• Original coding strand TCCGAGTATCAGTCCCAG...• Amino acid sequence SerGluTyrGlnSerGln .• If the second base is deleted:• Mutant coding strand TCGAGTATCAGTCCCAG....• Amino acid sequence SerSerIleSerPro . .• Mutations may occur in introns as well as exons• Mutation near either end of intron may cause a change in splicing of exons and produce abnormal protein• DNA alterations causing change in transcription or translation• Promoter site mutation• Enhancer mutation• Repressor mutation• micro RNA target mutation• Polygenic diseases (complex, multifactorial)– Disorder caused by collective action of alleles in many genes– Gene x environment interactions– Examples: Resistance to mastitis, Johne’s disease, bovine leukemia virus, milk fever, infertility, cancer, obesity, etc.Human Citrullinaemia• Citrullinemia belongs to a class of genetic diseases called urea cycle disorders• The urea cycle is a sequence of chemical reactions that takes place in liver cells.• These reactions process excess nitrogen that is generated when protein is used by the body.• The excess nitrogen is used to make a compound called urea, which is excreted in urine.• Citrullinaemia causes ammonia and other toxic substances to accumulate in the bloodUrea Cycle:-Is the sole source of endogenous production of arginine, ornithine, and citrulline; -Is the principal mechanism for the clearance of waste nitrogen resulting from protein turnover; -Is the principal mechanism for the metabolism of other nitrogenous metabolic compounds such as adenosine monophosphate;-Includes enzymes that overlap with the nitric oxide production pathway (ASS and ASL).Two Forms of Citrullinaemia:-They have different signs and symptoms and are caused by mutations in different genes.Type I: mutations in the ASS1Type II: mutations in the SLC25A13 geneCitrullinaemia in Humans Type I:-Mutations in the argininosuccinate synthase 1 (ASS1) gene-Mutations in ASS1 reduce the activity of the enzyme and prevents the body from processing nitrogen effectively.-Excess nitrogen (in the form of ammonia) accumulate in the bloodstream.-Ammonia is particularly toxic to the nervous system, which helps explain the neurologic symptoms (such as lack of energy, seizures, and ataxia) that are often seen in type I citrullinemia.-Affected infants typically appear normal at birth, but as ammonia builds up in the body they develop neurologic symptome-Affects about 1 in 57,000 human births worldwide Citrullinaemia in Humans Type II:-The signs and symptoms usually appear during adulthood and mainly affect the nervous system-Confusion, abnormal behaviors (such as aggression, irritability, and hyperactivity), seizures, andcoma-Mutations in the SLC25A13 (solute carrier family 25, member 13) gene are responsible for type II citrullinemia-This gene makes a protein called Citrin, which normally transports certain molecules in and out of mitochondria-Nonfunctional protein disrupts the urea cycle-Type II is primarily found in the Japanese population (1 in 100,000 to 230,000 individuals)Citrullinaemia in Cattle:• Normal at birth, but signs of depression within a few hours• Tongue protrusion • Unsteady walk• Blindness• Frothing at mouth• Head pressing• Death within 3-5 days because of ammonia poisoningCAUSES:-Single base substitution in the ASS gene: Arginine (CGA) in the 86th amino acid of the enzyme is replaced by a stop codon (TGA), a nonsense mutation.-Normal protein: 412 amino acids-Truncated protein: 85 amino acids-Heterozygous animals live normally but have 50% of normal enzyme activity-Affected animals are homozygous for the defective allele, produce no enzymeASS Deficiency:-Discovered in Australia -Australia: 1/250 calves affected; 10% of the Friesian cattle were carriers-Canadian bull Linmack Kriss King -Extensive use of L-K-K semen in Australia, New Zealand, and the UK.-The sire of L-K-K, Gray-View Crisscross (US), was a carrier-Crisscross was bred at Gray View Farms, Union Grove, WI -Less than 2,000 offspring in the