BMS 532 Neurogenetics & Structural Abnormalities PDF

Additional Inheritance and Human Pedigrees Questions An individual inherits a pathogenic variant of a gene: ◦ If the pathogenicity is inherited in an autosomal dominant manner, what are the possible genotypes of the parents? (LO3, LO5, LO6) ◦ If the pathogenicity is inherited in an autosomal re...

Additional Inheritance and Human Pedigrees Questions An individual inherits a pathogenic variant of a gene: ◦ If the pathogenicity is inherited in an autosomal dominant manner, what are the possible genotypes of the parents? (LO3, LO5, LO6) ◦ If the pathogenicity is inherited in an autosomal recessive manner, what are the possible genotypes of the parents? (LO3, LO5, LO6) ◦ Draw the pedigree adding in the following features: the individual is male, neither parent is affected, there are 3 siblings as follows: male with, male without, female without. The maternal grandfather was affected but the maternal grandmother was not (no additional relatives on maternal side). Neither paternal grandparent was affected and one additional child was also not affected. What would you expect for manifestation of a genetic disorder if disease phenotype is influenced by environment and no environmental triggers are present? (LO5, LO8) Gene Regulation Questions Which operon example is turned on when needed? (LO4, LO5) Which operon example also has significant translational regulation? (LO4, LO5) Translational regulation in eukaryotes can be thought of as a method that affects the level of translation and/or _________? (LO6) What is the role of mRNA higher order structures in regulation? (LO6) High levels of glucose are available in the environment along with high levels of lactose. What is the most likely consequence for the lac operon in terms of relative activity? (LO4, LO5, LO7) MORE LO7: What is the expected consequence in terms of gene expression for the following changes: constitutive binding of repressor to operator? constitutive binding of cAMP to operon? A change in sequence prevents mRNA folding. If folding was necessary to enable full transcription of the mRNA, what is the consequence in terms of functional product? Proteins and Protein Aggregation Questions A protein that does not spontaneously fold and is no longer capable of interacting with folding machinery would not be capable of what level(s) of protein structure? (LO1 and LO3) A structurally abnormal protein that is capable of inducing altered structure of normal protein variants would be classified as what and would most likely cause what? (LO1, LO4, and LO5) The genetic sequence of a protein whose active site is made available via conformational changes induced via phosphorylation is altered turning all serine sites to threonine. What is the potential consequence of this change? (LO6) Neurogenetics and Structural Abnormalities BMS 532 MOLECULAR BIOLOGY AND GENETICS BLOCK 4 LECTURE 4  Objectives 1. Define the following terms: neurogenetics, polygenic, congenital, phenotypic spectrum, syndactyly, and myopathy 2. Explain the role of genomic sequencing in modern neurogenetics and structural anomalies 3. Connect the following genes with their normal function, tissue activity, and most common pathogenic variations: ◦ APP, PSEN1, PSEN2, APOE, and APOE-ε4 (Alzheimer’s); WFS1 (Wolfram Syndrome 1); HTT (Huntington’s Disease); MTHFR (Spina Bifida and Myelomeningocele); HOXD13 (Syndactyly); and RYR1, MTM1, DNM2, TTN, MYH7, ACTA1, and NEB (Congenital Myopathies) 4. Identify the disease, phenotypic manifestations, and clinical expectations for a given pathogenic variant of the genes listed above 5. Assess the most likely gene involved from a list of clinical symptoms or provided a disease/syndrome with emphasis on the genes and conditions listed above 6. Compare and contrast the congenital myopathies to discriminate and identify the following with emphasis on discriminating phenotypic features, genes involved, expected inheritance patterns, and gene mutations that influence the expected inheritance patterns: ◦ Core myopathies, Nemaline myopathies, Centronuclear myopathies, and Myosin storage myopathies 7. Evaluate somatic changes in the mTOR pathway and explain their role in corresponding disease development LO1 Introduction to Neurogenetics Field of study emphasizing understanding the genetic underpinnings of neurological conditions Crosses-over with several other areas of molecular biology and genetics as there are neurological implications in many inherited and de novo genetic disorders Example Categories: ◦ Neurometabolic ◦ Channelopathies ◦ Disorders of Gene Regulation ◦ Neurologic Disorders caused by Sequence Repeats ◦ Peripheral inherited neuropathies LO1 Neurogenetics and Phenotypic Spectrums Neurogenetics provides valuable insights into complicated genetic interactions Not all changes in the same gene are created equal or cause identical outcomes Correlation between disease severity and type of genetic change with complex genetic interactions playing a role in activity and phenotype ◦ Additional variation can alter disease phenotypic manifestation (for better or worse) Congenital changes = changes that are present since birth ◦ Most commonly referred to in terms of structural anomalies LO1, LO2 Genetics of Neurologic Diseases Genome-wide association studies (GWAS) remains a valuable tool to identify the genetic alterations most likely to result in a disease phenotype/manifestation DNA sequencing has enabled the identification of rare single-gene mutations that correlate with a wide range of neurologic conditions ◦ As these tests advance and become more common across the population, results and identification of pathogenic variants improves ◦ Ex) Huntington’s disease, several Inborn Errors of Metabolism/Common Metabolic Disorders NOTE: Most common neurologic diseases are polygenic and complex LO1, LO3, LO4, LO5 Alzheimer’s Disease Most common neurodegenerative disorder Genetic studies have provided significant insights into this disease Autosomal Dominant Inheritance for many forms Rare, early onset forms are associated with mutations in: ◦ Amyloid beta (A4) precursor protein (APP) ◦ Presenilin 1 (PSEN1) ◦ Presenilin 2 (PSEN2) ◦ All 3 function in amyloid beta processing thus making this process a marker for Alzheimer disease Monogenic vs polygenic can be a factor of specific variations: ◦ Apolipoprotein E (APOE) = a major cholesterol carrier; correlated with autosomal dominant inheritance of Alzheimer’s (3 known pathogenic variants that are inherited autosomal dominantly) ◦ Changes in APOE alongside APP, PSEN1, or PSEN2 can modify the disorder (worse prognosis with earlier age of onset observed in many cases) ◦ Polygenic version is a specific APOE variant = APOE-ε4 ◦ Confers increased risk of Alzheimer’s disease development but is also correlated with cardiovascular disease risk LO1, LO3, LO4, LO5 Wolfram Syndrome 1 Rare neurogenetic disorder Highly variable syndrome but characterized by DIDMOAD: diabetes insipidus (excessive urine production), diabetes mellites (elevated blood glucose), optic atrophy, and deafness In general, inherited autosomal recessively due to mutations in the wolframin ER transmembrane glycoprotein gene (WFS1) (see top pedigree) Some WFS1 gene mutations can exhibit Dominant inheritance patterns (see bottom pedigree) but will not typically follow all aspects of WFS1 disease manifestation (i.e. will not have DIDMOAD) LO1, LO3, LO4, LO5 Huntington’s Disease Neurodegenerative disease (see previous slides) HTT gene = huntingtin (exact function unknown); clear role in neurons given implications of mutation Trinucleotide repeat expansion (CAG) results in disease phenotype ◦ 36 repeats = disease manifestation Number of copies of expanded gene inherited AND number of repeats for each gene contribute to disease phenotype ◦ Younger onset and more severe phenotype for homozygous and larger expansions LO1, LO3, LO4, Structural Abnormalities due to Genetic LO5 Mutation Classified as major structural anomalies or congenital anomalies Includes physical alterations of body parts including major organ systems Wide range of outcomes and possibilities including spectrum consequences Examples: ◦ Open Neural Tube Defects ◦ Spina Bifida = most common congenital defect of the central nervous system ◦ Myelomeningocele = most severe form ◦ Syndactyly = one of the most common congenital anomalies of the extremities and the most common congenital anomaly of the hand ◦ Congenital Myopathies = disorders present at birth that affect muscle (primarily referencing voluntary or skeletal muscle)  LO 11 Development of the Spinal ANATOMY Cord Callback A. Neural tube is created via neurulation ◦ Rostral and caudal neuropores close B. Neuroprogenitor differentiate into neuroblasts and proliferate A B C. Alar plate posterior horn ◦ Remaining neural crest cells will form dorsal root ganglion with sensory neuron cell bodies within; axons grow out to form dorsal root D. Basal plates anterior horn ◦ Contain motor neuron cell bodies; axons will grow from neuronal cell bodies Neural canal becomes central canal C D Before We Are Born, Moore et al., 2020  Development of the Dermatomes and Myotome Patterns LO 11 Somites from paraxial mesoderm form dermamyotome Axons from future spinal nerves grow into dermamyotome; are pulled along during migration of future muscles and skin ◦ Segmental distribution of dermatomes and myotomes results from this migration ANATOMY Callback Gray’s Basic Anatomy, Drake et al., 2018 LO1, LO3, LO4, LO5 Spina Bifida and Myelomeningocele Complicated inheritance pattern involving multiple genes AND a combination of variants at multiple loci Several genes have exhibited autosomal dominant inheritance though environmental influences cannot be ignored (FOLIC ACID intake) Associated Genes: ◦ Homocysteine-folate metabolism enzymes: methylenetetrahydrofolate reductase (MTHFR), methionine synthase (MS), cobalamin coenzyme synthesis, and cystathionine b-synthase (CBS) ◦ Planar Cell Polarity (PCP) pathway genes: core PCP scaffold proteins (VANGL1 and VANGL2), Fuzzy planar cell polarity (FUZ), Cadherin EGF LAG seven-pass G-type receptor (CELSR1) ◦ Additional Genes: several additional genes have been implicated with a wide range of mutations  LO 10b Development of the Limbs Limb buds grow on three axes ◦ Proximodistally ◦ Apical ectodermal ridge (AER) induces growth and development in limb mesenchyme ◦ Anteroposteriorally ◦ Zone of polarizing activity is induced by AER to control anterior/posterior limb patterning (radial/ulnar) ◦ Dorsoventral ANATOMY ◦ Induced by dorsal and ventral epidermis of limb buds, respectively Callback ◦ Future flexors and extensors Mesenchymal cells proximal to AER differentiate into blood vessels and cartilaginous bone models https://en.wikipedia.org/wiki/Zone_of_polarizing_activity  LO 10c Development of the Limbs Week 5 ◦ Limb buds are present Week 6-7 ◦ Hand and foot plates develop ◦ Digital rays form ◦ AER at the tip of each digital ray induces primordia of bones (phalanges) ◦ Apoptosis of loose mesenchyme between developing digits occurs ◦ Cartilaginous models are formed ANATOMY End of week 7 ◦ Limb rotation occurs Callback LO1, LO3, LO4, LO5 Syndactyly Soft tissue fusion of adjacent digits affecting hands and/or feet Results from: ◦ Failure in apoptosis separating the mesenchymal tissue or ◦ Failure of notch formation in the apical ectodermal ridge Generally categorized as simple, complex, or complicated ◦ Presence of bony fusion = complex form ◦ Additional bones or ligament involvement = complicated Autosomal dominant inheritance with incomplete penetrance but also associated with several genetic syndromes ◦ Males to females = nearly 2 to 1 Multiple genes implicated including HOXD13 LO1, LO3, LO4, LO5, LO6 Congenital Myopathies Group of rare hereditary muscle diseases ◦ Architectural abnormalities in muscle fibers 5 subgroups ◦ Core myopathies ◦ Nemaline myopathies ◦ Centronuclear myopathies ◦ Congenital fiber type disproportion myopathy* ◦ Myosin storage myopathy Muscle biopsy, muscle imaging, and genetic analysis are all essential to diagnosis Symptoms manifest at birth or infancy typically though adolescent and adult onset more recently identified Complex inheritance patterns where specific mutations even in the same gene may be inherited autosomal dominantly or autosomal recessively *we will not focus on this type or its inheritance so consider it in terms of question distractors only MPP1 Callback ”Take Home” Figure LO3, LO4, LO5, LO6 Differentiating Features CORE MYOPATHIES NEMALINE MYOPATHIES Presence of cores/minicores in the muscle fibers Presence of nemaline bodies/rods in the ◦ Areas of myofibrillar disruption lacking sarcoplasma and/or nuclei of muscle fibers mitochondria More than 14 genes implicated Visualizable via lack of oxidative enzyme activity ◦ Central core = 1 large ‘core’ where activity is absent Different inheritance patterns based on gene involved ◦ Minicores = multiple focal areas of absent activity Skeletal muscle alpha-actin gene (ACT1) Multiple genes implicated ◦ Accounts for more than 50% of the severe cases RYR1 mutations most common in central core Nebulin (NEB) myopathy ◦ Associated with “typical” nemaline myopathy and ◦ major sarcoplasmic reticulum calcium release represents 50% of all cases channel of the skeletal muscle MPP1 Callback Excitation-Contraction Coupling T-tubule ◦ L-type Ca++ channels (DHP) ◦ Tetrads Mechanics: 1. AP enters T-tubule from sarcolemma 2. DHP receptor opens RyR on SR open 3. Ca++ floods out of SR Guyton and Hall Medical Physiology 13th ed LO3, LO4, LO5, LO6 Differentiating Features CONGENITAL FIBER TYPE DISPROPORTION CENTRONUCLEAR MYOPATHIES MYOPATHY* Centralized nuclei that are larger than normal Defined by selective atrophy of type 1 muscle and commonly with a vesicular appearance fibers (may be absent other anomalies) ◦ Diameter of type 1 fibers typically 35-40% Muscle weakness and wasting with variable smaller in diameter than type 2 fibers age of onset 10 genes associated with both autosomal Variable inheritance based on gene dominant and autosomal recessive inheritance >9 genes identified with 3 serving as *we will not focus on this type or its inheritance so consider it in potentially main causes: MTM1, DNM2, and terms of question distractors only TTN MPP1 Callback Excitation-Contraction Coupling T-tubule ◦ L-type Ca++ channels (DHP) ◦ Tetrads Mechanics: 1. AP enters T-tubule from sarcolemma 2. DHP receptor opens RyR on SR open 3. Ca++ floods out of SR Guyton and Hall Medical Physiology 13th ed LO3, LO4, LO5, LO6 A little more about T-tubules MTM1 = myotubularin ◦ membrane bound lipid phosphatase DNM2 = dynamin 2 ◦ Ubiquitously expressed GTPase These molecules have roles in tubule formation (T-tubules) and therefore play a role in the excitation-contraction coupling MPP1 Callback Structural Proteins of the Sarcomere Numerous cytoskeletal proteins constrain the thick and thin filaments to aid in its assembly and maintenance 1. α- Actinin ◦ Binds the ends of thin filaments to the Z disks 2. Titin ◦ Huge protein, one end is attached to a Z disk, the other to the thick filaments ◦ Forms a spring that limits how much the sarcomere can be stretched. It also centers the thick filaments within the sarcomere 3. Dystrophin ◦ Large protein associated with Z disks ◦ Anchors the contractile array to the cytoskeleton and surface membrane ◦ It also aligns the Z disk with disks in adjacent myofibrils and muscle fibers LO3, LO4, LO5, LO6 Differentiating Features MYOSIN STORAGE MYOPATHY FINAL SUMMARY Formerly hyaline body myopathy The genetics of congenital myopathies are complicated and variable Presence of hyaline bodies Key genes may be associated with key clinical mutations most commonly in Myosin heavy findings and genetic causes may overlap in the chain 7 (MYH7) conditions ◦ MYH7 is also associated with cardiomyopathy and is linked to the cardiovascular abnormalities of the congenital myopathies LO3, LO4, LO5 Clinical Features Correlate with Key Genes All congenital myopathies have marked muscle Clinical Feature Key Genes weakness with potential for additional muscular deficits such as wasting (atrophy) or progressive Eye involvement DNM2, MTM1, RYR1 loss of muscle tone Cardiac involvement ACTA1, MYH7, TTN Quick Gene Reference Marked congenital hypotonia MTM1, RYR1 ◦ ACTA1 = alpha-skeletal actin Respiratory involvement out of ACTA1, NEB, SEPN1, ◦ DNM2 = dynamin 2 proportion to skeletal muscle TPM3 ◦ MTM1 = myotubularin weakness ◦ MYH7 = slow skeletal beta-cardiac myosin ◦ NEB = nebulin Severe respiratory involvement at MTM1, severe RYR1 ◦ RYR1 = ryanodine receptor 1 birth ◦ SEPN1 = selenoprotein 1 Facial dysmorphism (elongated face, Severe DNM2, MTM1, ◦ TPM3 = slow alpha-tropomyosin high arched palate, dolichocephaly) severe RYR1 ◦ TTN = titin LO2, LO3, LO4, LO5, LO6 Inheritance Patterns Although each of the congenital myopathies can be caused by a variety of genes, there are common changes observed for each Inheritance patterns vary depending on the specific genetic mutation The table on the next slide summarizes the most commonly associated gene with the inheritance pattern described as well as the most common changes observed for the implicated gene Gene sequencing is CRITICAL to proper identification of the genes and inheritance patterns for these conditions LO3, LO4, LO5, LO6 Inheritance Patterns Condition Inheritance Pattern Most Common Most Common change and additional information Gene Implicated Central core Myopathy Autosomal Dominant RYR1 Missense Central core myopathy Autosomal Recessive RYR1 Biallelic mutations; variable missense and nonsense Nemaline Myopathy Autosomal Dominant ACTA1 Missense (often heterozygous) Nemaline Myopathy Autosomal recessive NEB Splice site mutations, frameshifts (+ or -