Genetics and heredity in orthodontics/certified fixed orthodontic courses by Indian dental academy

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Genetics and heredity in orthodontics/certified fixed orthodontic courses by Indian dental academy

  1. 1. www.indiandentalacademy.com INDIAN DENTAL ACADEMY Leader in continuing dental education www.indiandentalacademy.com
  2. 2. GENETICS AND HEREDITY www.indiandentalacademy.com
  3. 3. CONTENTS Introduction History Principles of genetics Molecular basis and biology of genetics Tools for molecular biology Human genome project Modes of inheritance Genetic abnormalities Genetic risk assessment Genetic counseling Bioethics Conclusion References www.indiandentalacademy.com
  4. 4. introduction www.indiandentalacademy.com
  5. 5. Genetics: The branch of science concerned with the means and consequences of transmission and generation of the components of biological inheritance . Heredity : The transmission of characters from parent to offspring by information encoded in the parental germ cells . www.indiandentalacademy.com
  6. 6. HISTORY Gregor Mendel is considered the ‘Father of genetics’. He selected seven contrasting character in garden peas. He enunciated the principles of heredity : 1.The law of uniformity. 2.The law of segregation of alleles. 3.The law of independent assortment. www.indiandentalacademy.com
  7. 7. www.indiandentalacademy.com
  8. 8. Galton (1875) initiated the idea of polygenic inheritance. Garrod (1902) Landsteiner[1900] discovered ABO blood groups. Hardy and Weinberg – population genetics. Watson and crick Discovered the double helix model of DNA www.indiandentalacademy.com
  9. 9. www.indiandentalacademy.com
  10. 10. Principles of genetics Chromosomes and DNA replication 1. Organization of DNA into chromosomes . • Human genome Principle :Method of things operation. The ultimate source, origin or cause of something. www.indiandentalacademy.com
  11. 11. 2.Replication of DNA and mitosis www.indiandentalacademy.com
  12. 12. 3. Assortment and segregation of genes during meiosis. www.indiandentalacademy.com
  13. 13. Regulation of gene expression – Transcription – Post transcriptional modifications – m-RNA processing – Translation – Post translational modifications www.indiandentalacademy.com
  14. 14. Cloning, nucleic acid hybridization and DNA sequencing • Cloning : creation of a recombinant DNA molecule that can be propagated indefinitely. www.indiandentalacademy.com
  15. 15. • Nucleic acid hybridization : It is a fundamental principle in molecular biology that takes advantage of the fact that the two complementary strands of nucleic acid bind or hybridize to one another with very high specificity. • DNA sequencing : A chemical process known as dideoxy-sequencing allows the identification of the exact nucleotide sequence of a piece of DNA. www.indiandentalacademy.com
  16. 16. Mutations : A mutation can be defined as any change in the primary nucleotide sequence of DNA regardless of its functional consequences. • Point mutations : Involve single nucleotides. • Transitions : Substitutions, if a purine is replaced by another purine. • Transversions : Changes from purine to pyramidine or vice versa. • Missense mutation : DNA sequence change occurs in coding region and alters an amino acid. www.indiandentalacademy.com
  17. 17. Molecular basis and biology of genetics DNA structure and function : • DNA is made up of deoxyribose- phosphate backbone and a series of purine: adenine (A) and guanine (G) pyrimidine: thymidine (T) and cystine (C) bases of nucleic acid. www.indiandentalacademy.com
  18. 18. • Complementarity allows the transmission of genetic information from DNA RNA  protein. • It is possible to arrange the 4 bases into 64 different triplet codons (43). By arranging the codons in different combinations and in various lengths, it is possible to generate the tremendous diversity of primary protein structure. www.indiandentalacademy.com
  19. 19. Nucleoside: a compound of a sugar with a purine or pyramidine base by way of an N glycosyl link. Nucleotide: a combination of a purine or pyramidine, one sugar and a phosphate group. www.indiandentalacademy.com
  20. 20. Genes • A gene is a portion of DNA that contains the codes for polypeptide sequence. • Genes vary greatly in size : most of them extend over 20-40 kbp. www.indiandentalacademy.com
  21. 21. • Exons : portion of genes that are eventually spliced together to form mRNA. • Introns : spacing regions between the exons that are spliced out of precursor RNAs during RNA processing. www.indiandentalacademy.com
  22. 22. • The regulatory regions in genes most commonly involve sequences upstream (5’) of the transcription start site. The upstream regulatory genes are also referred to as promoters. • Transcriptional termination signals reside down stream (3’) of a gene. • 5’  3’ Direction of transcription of genetic information • Key regulatory elements. Eg. globin and immunoglobin genes www.indiandentalacademy.com
  23. 23. Chromosomes : Higher eukaryotes have their genomic packages – chromosomes, separated from the general cytoplasm by nuclear envelope. histones. Heterochromatin : These regions tend to be super coiled around histones in condensed regions. Euchromatin : Most the DNA regions, those coding for proteins are relatively uncondensed during interphase and constitute the euchromatin. www.indiandentalacademy.com
  24. 24. www.indiandentalacademy.com
  25. 25. Transcription and translation •Transcription •Post transcription modification •m-RNA processing •Translation •Post translation modification •Stop codons : UAA,UAG,UGA •Transcriptional controlwww.indiandentalacademy.com
  26. 26. Translation www.indiandentalacademy.com
  27. 27. Tools for molecular biology 1) Restriction enzymes : Genomic DNA can be cut into a number of fragments by enzymes called restriction enzymes which are obtained from bacteria. Eg. : Enzyme EcoRI. 2) Gel electrophoresis : As DNA is negatively charged molecule, the genomic DNA that has been digested with a restriction enzyme can be separated according to size and charge by electrophoresing DNA through gel matrix. • Pulsed field gel electrophoresis. www.indiandentalacademy.com
  28. 28. 3) Southern blotting and DNA probes : • Southern blotting allows the visualization of individual DNA fragments. • DNA probes are useful to indicate where the fragment of interest lies. 4) Northern blotting and western blotting : • Northern blotting is used to visualize RNA fragments on to membrane. • Western blotting is used to visualize proteins. www.indiandentalacademy.com
  29. 29. Southern blotting and DNA probes. www.indiandentalacademy.com
  30. 30. 5) Polymerase chain reaction : Minute amounts of DNA can be amplified over a million times within a few hours using this invitro technique www.indiandentalacademy.com
  31. 31. 6) DNA cloning Recombinant DNA technique, showing incorporation of foreign DNA into plasmid. Ampicillin resistant genes can be used to distinguish transformed E. coli cells www.indiandentalacademy.com
  32. 32. 7) DNA libraries These are pools of isolated and cloned DNA sequences that form a permanent resource for further experiments. 2 types of libraries : – Genomic libraries -contains almost every sequence in the genome. – cDNA libraries - contain sequences derived from all mRNAs expressed in that tissue. 8) DNA sequencing : Used to identify the exact nucleotide sequence of a piece of DNA.www.indiandentalacademy.com
  33. 33. The human genome project : The HGP was initiated in the mid 1980’s to characterize the human genome, culminating in a complete DNA sequence. Main goals of HGP include : – Creation of genetic maps – Development of physical maps – Determination of the complete human DNA sequence. Genetic map Physical map HGP was completed in June 2000. www.indiandentalacademy.com
  34. 34. Modes of inheritance : • An inherited trait may depend on a single gene pair or on the cumulative effect of a large number of genes. • The former is called Mendelian or unit factor inheritance. The latter is called polygenic inheritance. Mendelian inheritance  Autosomal inheritance • Autosomal dominant • Autosomal recessive When the two members of an allelic pair are identical, they are said to be homozygous and when they are unlike each other the combination is said to be heterozygous. • A trait is said to constitute the phenotype of an individual, while the allelic pair of genes determining the trait constitute the genotype for that trait. www.indiandentalacademy.com
  35. 35.  Sex-linked inheritance : Inheritance through the genes carried on sex chromosomes X and Y. X-linked inheritance : • A male has only one representative of any X-linked gene a hence is said to be hemizygous rather than homozygous or heterozygous. • X-linked recessive : eg. Hemophilia. • X-linked dominant. Eg. Vit. D Resistant rickets, Xg blood group. Y-linked inheritance : holandric inheritance (because only in males) Eg. Hairy ears. Polygenic inheritance (multifactorial) www.indiandentalacademy.com
  36. 36. GENETIC ABNORMALITIES Cherubism : • Occurs as an autosomal dominant disorder and with 100% penetrance in males and 50 to 75% penetrance in females, with 2:1 male predominance. • Marked fullness of the jaws. www.indiandentalacademy.com
  37. 37. •Ectopic eruption, severe malocclusion. •Permanent teeth may be missing or malformed as the developing tooth follicles are displaced. www.indiandentalacademy.com
  38. 38. Osteogenesis imperfecta : • Caused by mutations that cause a quantitative defect in production of type I collagen. • OI is the probably the most common inherited bone disease.  OI type I : autosomal dominant, most common.  OI type II : autosomal recessive, most severe.  OI type III : both AD and AR.  OI type IV : AD. • Classically this condition includes fragile bones, blue sclerae, ligamentous laxity, hearing loss and dentinogenesis imperfecta. www.indiandentalacademy.com
  39. 39. • Primary teeth are more severely affected than the permanent teeth. • Crowns are described as shortened and bell shaped with cervical constriction. www.indiandentalacademy.com
  40. 40. Cleidocranial dysplasia : • Inherited as AD with high penetrance with wide variability in expression. • A gene for this disorder has been mapped to chromosome 6p21. www.indiandentalacademy.com
  41. 41. • Maxillary hypoplasia gives the mandible a relatively prognathic appearance. • Palate is narrow and high arched. • Increased incidence of submucosal clefts and complete or partial clefts of the palate involving the hard and soft tissues. • Non union of symphysis of mandible. • Unerupted supernumerary teeth. www.indiandentalacademy.com
  42. 42. Crouzon’s syndrome (Craniofacial dysostosis) : • AD with complete penetrance and variable expressivity. • Mutation in the fibroblast growth factor receptor 2 gene (FGFR2) which maps to chromosome 10q25-q26, cause this syndrome. • Shallow orbits are the most common feature. • Frog like facies. Midface hypoplasia and exopthalmos are striking. www.indiandentalacademy.com
  43. 43. • Mandibular prognathism with nose resembling parrot’s beak. • Maxillary hypoplasia, high arched palate. • Bilateral posterior lingual cross bites. • Anterior open bite. www.indiandentalacademy.com
  44. 44. Treacher Collins syndrome (mandibulofacial dysostosis) : • AD with high degree of penetrance but variable expressivity. • Mutation in a gene of unknown function referred to as treacle which maps for 5q 32 – 33.1 are responsible. • Facial appearance is characteristic and is often described as bird like or fish like. www.indiandentalacademy.com
  45. 45. • Includes various degrees of hypoplasia of the mandible, maxilla, zygomatic process of temporal bone, external and middle ear. • Oral finding include cleft palate, macrostomia, high arched palate, dental malocclusion consisting of apertognathia and widely separated and displaced teeth. • The peculiar broad and concave nature of the inferior border of the mandible is characteristic. www.indiandentalacademy.com
  46. 46. Pierre Robin syndrome : • Fetal malposition and interposition of the tongue between the palatal shelves is probable etiology. • Severe micrognathia and mandibular hypoplasia. • U shaped cleft palate is common. • Glossoptosis • High arched palate sometimes. www.indiandentalacademy.com
  47. 47. Down syndrome (Trisomy 21) : • Incidence – 1 in 600-700. • Most cases of trisomy 21 are caused by non disjunction, resulting in an extra chromosome. • Skull is brachycephalic with flat occiput and prominent forehead. • Frontal, sphenoid sinuses absent and maxillary sinus is hypoplastic. www.indiandentalacademy.com
  48. 48. • Fissured tongue, Macroglossia. • Open mouth posture • Palatal width and length are significantly decreased, bifid uvula, cleft lip and palate. • Delayed eruptions, hypodontia, microdontia, crown root malformations. • Occlusal disharmonies, posterior crossbites, apertognathia, severe anterior teeth crowding. www.indiandentalacademy.com
  49. 49. Hemifacial atrophy : • Progressive unilateral atrophy of the face. • Tongue, lips and salivary glands may show hemiatrophy. • Developing teeth may show incomplete root development and delayed eruption. www.indiandentalacademy.com
  50. 50. Cleft lip and palate : • Majority of cases of cleft lip or cleft palate or both can be explained by the multifactorial threshold hypothesis (polygenic inheritance). • Abnormalities of tooth number, size, morphology, calcification and eruption. • Prevalence of hypodontia increase with severity. • Tooth formation often delayed and enamel hypoplasia, microdontia or macrodontia and fused teeth are seen frequently. www.indiandentalacademy.com
  51. 51. Macroglossia :  Down syndrome  Hunter syndrome  Hurler syndrome  Maroteaux lamy syndrome www.indiandentalacademy.com
  52. 52. Microglossia :  Oromandibular – limb hypogenesis spectrum.  Moebius sequence.  Freeman Sheldon syndrome www.indiandentalacademy.com
  53. 53. Amelogenesis imperfecta : • AI represents a group of hereditary defects of enamel unassociated with any other generalized defects. • Types : • Hypoplastic – mainly AD. • Hypocalcified – AD & AR. • Hypomaturation – AD & AR. www.indiandentalacademy.com
  54. 54. Dentinogenesis imperfecta : • The association between DI and OI is well recognized although each condition may occur independently • Type I – AD generally. Both DI and OI present • Type II – Never occurs with OI. Autosomal dominant. • Type III – Brandywine type. Same clinical appearance of teeth as types 1 and 2 but it may also show multiple pulp exposures in deciduous teeth. www.indiandentalacademy.com
  55. 55. Genetic risk assessment : • One of the most important aspects of genetic counseling is the provision of a risk figure. Probability / probability of recurrence (P) : Probability of an outcome can be defined as the number or more correctly, the proportion of times it occurs in a large series of events. Probability is indicated as a proportion of 1. Probability theory : • Laws of addition and multiplication www.indiandentalacademy.com
  56. 56. Baye’s theorem : It provides a very valuable method for determining the overall probability of an event or outcome, such as carrier status by considering all initial possibilities, eg. carrier or non carrier and then modifying or conditioning these by incorporating information. www.indiandentalacademy.com
  57. 57. •Anterior information •Prior probability •Posterior information •Conditional probability •Joint probability •Relative probability www.indiandentalacademy.com
  58. 58. Risks in multifactorial disorders : • One of the basic principles in the multifactorial inheritance is that the risk of recurrence in first degree relatives, siblings and offspring, equals the square root of incidence of the disease in the general population i.e. P 1/2 where P equals the general population incidence. • The theoretical risks for 2nd and 3rd degree relatives can be shown to approximate to P 3/4 and P 7/8 respectively. www.indiandentalacademy.com
  59. 59. Genetic counseling: • Patients with a great variety of diseases and syndromes are now referred for evaluation and counseling. • Genetic evaluation and counseling has become team affair. • The traditional role of counselor is to estimate P, the probability of recurrence. • Family physician is the most appropriate person to do the counseling because he know the family, its attitudes and socioeconomic background better than a consultant. www.indiandentalacademy.com
  60. 60. Evaluation of the patient : • The genetic evaluation of the family begins well before the genetic counseling process.  Does the patient have a disease of clearly non genetic origin, such as infection or birth trauma ?  Does the baby have a disease of clear genetic etiology, such as haemophilia ?  If the patient’s disorder doesn't fall into either of the above categories, does the patient have features that suggest a syndrome ?  When a syndrome cannot be identified, one must consider what further investigations are necessary. Is examination of the chromosomes indicated ? • In any case, the family history should be screened for clues to the possible genetic basis for baby’s problem. www.indiandentalacademy.com
  61. 61. Genetic counseling – Aims :  Obtaining a full and careful history.  Establishing an accurate diagnosis.  Drawing a family free is essential.  Estimating the risk of a future pregnancy being affected of carrying a disorder.  Information giving  Continued support and follow up.  Genetic screening – includes prenatal diagnosis, carrier detection.www.indiandentalacademy.com
  62. 62. Bioethics in genetics • In no other area of biomedical research there has been a greater concern for ethical issues than in the field of human genetics. • Serious issues related to the participation of human subjects in genetic research are raised particularly when the intervention involves rights of human embryo and subjects who are not competent to give informed consent. • Recent experiments on cloning sheep and mice have brought human cloning into the realm of possibility, raising additional set of ethical legal and social issues.www.indiandentalacademy.com
  63. 63. General guidelines : • Clinical research besides being subject to general ethical considerations of protection from harm and voluntaries of participation has following addition considerations:  The harm may not only be physical but also psychosocial.  Maintaining confidentially of research findings.  Genetic counseling is akin to therapy. Written explanation about presentation and natural courses of disease, interventions, etc has special place in clinical research.  Genetic manipulations have consequences for future, some of which are unknown. Hence, greater care towards potential dangers is necessary.  Institutional ethical committee.  Prenatal diagnostic techniques act 1994. www.indiandentalacademy.com
  64. 64. Ethical issues : • Pedigree studies • Genetic screening : Screened subjects are entitled to receive information in a way that : They can understand what is proposed to be done. They must be made aware of any substantial risk. They must be given time to decide whether or not they would like to participate or not. • Therapeutic trials including gene therapy : Recombinant protein products Gene therapy Somatic cell gene therapy Germ line therapywww.indiandentalacademy.com
  65. 65. Gene therapy for enhancing characters. Eugenic genetic engineering. • DNA banking • DNA diagnosis  Pre morbid diagnosis in children.  Pre morbid diagnosis in adults.  DNA diagnosis in forensics. • Prenatal diagnosis • Assisted reproductive techniques  Cloning : Since its safety, success, utility and ethical acceptability is not yet established, research on cloning with intent to produce an identical human being as of today is prohibited. www.indiandentalacademy.com
  66. 66. www.indiandentalacademy.com
  67. 67. www.indiandentalacademy.com
  68. 68. www.indiandentalacademy.com
  69. 69. REFERENCES : Emery’s elements of medical genetics. – Robert F. Mueller, Ian D. Young. – 11th edition. Kumar and Clark – Clinical medicine. – Praveen Kumar – Michael Clark – 5th edition. Harrison’s – Principles of internal medicine. – Volume 1, 5th edition. Medical genetics - Jorde, Carey - 5th edition Essentials of Human genetics -Bhatnagar, Kothari, Mehta www.indiandentalacademy.com
  70. 70. Text book of oral pathology - Shafer - 4th edition Indian council of medical research. API textbook of medicine. – Siddharth N. Shah – 7th edition. Smith’s – Recognizable patterns of human malformation. – Kenneth Lyons Jones. – 5th edition. Oral pathology – Regezi and Sciubba. - Clinical pathologic correlations. - 3rd edition. www.indiandentalacademy.com
  71. 71. Next seminar is by Dr.Bhuvaneshwari on Hinge axis www.indiandentalacademy.com
  72. 72. www.indiandentalacademy.com
  73. 73. Thank you For more details please visit www.indiandentalacademy.com www.indiandentalacademy.com

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