GENETIC DISORDERS
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INDIAN DENTAL ACADEMY Leader in continuing dental education www.indiandentalacademy.com
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INTRODUCTION COMMON TERMINOLOGIES CLASSIFICATION ROLE OF HOMEOBOX GENES COMMON CRANIOFACIAL DISORDERS CONCLUSION
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INTRODUCTION Genes are the basic hereditary units , represent smallest physical & functional units of inheritance that resides in specific sites loci in the genome. Genome contains the entire genetic content of a set of chromosomes within a cell or an organism.
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Gene can be defined as entire DNA sequence necessary for synthesis of a functional polypeptide molecule.( mRNA, tRNA). They govern our physical and medical characteristics, such as hair color, blood type and susceptibility to disease. Genotype refers to the genetic constitution of an individual.
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Phenotype is the final product of a combination of genetic and environmental influences. Can be either a specified character or to all observable characteristics of individual. Proportion of phenotypic variance attributable to genotype is referred as Heritability.
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Chromosomes - Chromosomes are the structures that hold our genes . Found in nucleus. Each chromosome has a p and q arm; p is the shorter arm and q is the longer arm. The arms are separated by a pinched region known as the centromere. The typical number of chromosomes in a human cell is 46 - two pairs of 23 - holding an estimated 30,000 to 35,000 genes. The first 22 pairs of chromosomes are called "autosomes" and the final pair is called the "sex chromosomes." The sex chromosomes an individual has determines that person's gender; females have two X chromosomes (XX), and males have an X and a Y chromosome (XY).
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Chromosome map, of all 46 chromosomes is called a karyotype. The karyotype can help identify chromosome abnormalities that are evident in either the structure or the number of chromosomes Alleles – Genes at the same locus on a pair of homologous chromosomes. When both members of a pair of alleles are identical , individual is homozygous for that locus. When the 2 alleles at a specific locus are different, individual is heterozygous for that locus. www.indiandentalacademy.com
Trait – is a particular aspect or characteristic of the phenotype. Can be – Monogenic or Polygenic/Multifactorial traits. Monogenic – These develop because of influence of single gene locus. They can also be described as discrete or qualitative.
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Autosomal dominant trait – If having only one particular allele of the 2 alleles on a homologous pair of autosomes is sufficient to produce that trait/disease. Only one defective gene can produce disease. It has following characteristics – a) Every affected person has atleast one affected parent. Affected individuals may be homozygous or heterozygous for that abnormal gene. B) Both sexes are affected. C) Affected persons typically transmit the trait to half their offspring. D) Transmission is usually seen with no skipping of generation. www.indiandentalacademy.com
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Autosomal recessive trait – If 2 copies of defective gene are required for expression of trait. So disease happens only when both genes at a given locus on homologous chromosomes are defective. Concept of gene carrier is used with autosomal recessive traits. Characteristics – a) Trait usually appear in siblings & not in their parents. B) On an average one in four of siblings is affected. C) Males & females tend to be equally affected. www.indiandentalacademy.com
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X linked traits – Full expression of rare X linked recessive phenotypes is almost completely restricted to males. X linked recessive genes must be present at same locus in females to express themselves fully.
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Multifactorial inheritance – Here trait is determined by interaction of a number of genes at different loci, each with small but additive effect together with enviornmental factors. Many congenital malformations & common diseases of adult life are inherited as multifactorial traits.
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Categorization of Multifactorial Traits I. Discontinuous multifactorial traits: Traits determined by multiple gene loci, which are present or absent depending on the number or nature of the genetic, and/or environmental factors acting. There is an underlying scale of continuous variation of liability to develop the condition resulting from a combination of all the genetic and environmental influences involved. The condition is present only when the liability exceeds a critical threshold value. www.indiandentalacademy.com
More than 20 discontinuous multifactorial traits have been described in humans. Cleft lip and palate is a congenital malformation inherited as a discontinuous multifactorial trait. In the mildest form the lip alone is unilaterally cleft, whereas in the most severe form the lip is bilaterally cleft and the palatal cleft is complete. The parents of a cleft lip and palate are often unaffected, and there may be no family history of cleft lip and palate, but by producing an affected child the parents are deemed to have some underactive genes for cleft lip and palate formation. Only when the balance exceeds a certain threshold will the malformation occur, and the further the threshold is exceeded, the greater the extent of the malformation.
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II. Continuous multifactorial traits: Many normal human characteristics are determined as continuous multifactorial traits. These traits by definition have a continuously graded distribution e.g. for height there is a range from the very tall to the markedly short with the mean of 169 Âą 6.5 cm in English males (Connor and Ferguson Smith, 1993). The majority of individuals are centered around the mean. Such distribution is characteristic of a continuous multifactorial trait. Malocclusion should be regarded not as abnormal or as a disease, but as a variation of occlusion in a continuous multi-factorial trait
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Population genetics – Two terms used in population genetics are – a) Penetrance – It is a statistical term & indicates the proportion of individuals carrying a certain gene who can be detected. As ability to detect the expression of gene improves, penetrance increases. b) Expressivity – refers to degree of expression of a gene in an individual. More the expressivity more severe the disease. www.indiandentalacademy.com
Recent advances in molecular biology and in human genetics have had a considerable influence in the understanding of orofacial genetics. Some insight into the genetic mechanisms involved in craniofacial morphogenesis at the molecular level in the embryo assists our appreciation of the role of genetics, not only in the etiology of craniofacial abnormalities, but also in the regulation of maxillary, mandibular, and tooth morphology. www.indiandentalacademy.com
Many different types of genes are involved in developmental regulation – master regulatory genes. These genes encode transcription factors that regulate the expression of genes in nucleus. Ex – Homeobox genes are important regulators of craniofacial development. www.indiandentalacademy.com
Genes in signaling network – Regulate communication between nearby cells through a central mechanism by which the advancing development of embryo is regulated. The signal molecules (growth factors) belong to several families , ex – hegdgehogs (hh) , bone morphogenetic proteins (BMP) , fibroblast growth factor (FGF), Wnt family signalling molecules. Deficient function of several genes encoding FGFs, BMPs result in early embryonic lethality because they regulate early cell & tissue organization. www.indiandentalacademy.com
Role of Homeobox genes: Edward Lewis was the first person to identify the homeotic genes in the fly, which help in controlling the developmental response of groups of cells along the body’s antero-posterior axis. In animals, these genes-homeobox genes, are regarded as master genes of the head and face. The first vertebrate homeobox gene was cloned in the frog ( Xenopus levis) and was soon followed by cloning in mouse. www.indiandentalacademy.com
The vertebrate genes are called HOX genes and consist of 39 genes in humans as well as mice. They are arranged in 4 different clusters- HOX A, HOX B, HOX C, HOX D, on 4 different chromosomes. As the neural crest cells migrate from the rhombomeres to the specific branchial arches, they retain a specific homeobox code, which specifies the form and pattern of different derived regions of the head and neck.
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The sub-families of the HOX genes which are of particular interest in craniofacial patterning and morphogenesis, include: Muscle segment (Msx) Distal-less (Dlx) Goosecoid (Gsc) Otx gene. Bar Class Paired related genes (Prx and SHOT) LIM homeobox gene. www.indiandentalacademy.com
The expressions of these genes are mediated through two main groups of regulatory proteinsthe Growth factor family and the Steroid/Thyroid/ Retinoic acid Super family. Some of the important regulatory molecules in the mesenchyme, through which homeobox genes information is expressed at the cellular level are: Fibroblast Growth Factor (FGF) Epidermal Growth Factor (EGF), Transforming Growth Factors (TGFι, TGFβ) Bone Morphogenetic Proteins (BMPs) . www.indiandentalacademy.com
Genetic causes of malformations A Chromosomal abnormalities. B Single gene mutations. C Multifactorial
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Chromosomal abnormalities There are many types of chromosome abnormalities. However, they can be organized into two basic groups: Numerical Abnormalities: When an individual is missing either a chromosome from a pair (monosomy) or has more than two chromosomes of a pair (trisomy). An example of a condition caused by numerical abnormalities is Down Syndrome, also known as Trisomy 21 (an individual with Down Syndrome has three copies of chromosome 21, rather than two). Turner Syndrome is an example of monosomy 13 the individual is born with only one sex chromosome, an X. www.indiandentalacademy.com
Structural Abnormalities: When the chromosome's structure is altered. This can take several forms: Deletions: A portion of the chromosome is missing or deleted. Duplications: A portion of the chromosome is duplicated, resulting in extra genetic material. Translocations: When a portion of one chromosome is transferred to another chromosome. There are two main types of translocations. In a reciprocal translocation, segments from two different chromosomes have been exchanged. In a Robertsonian translocation, an entire chromosome has attached to another at the centromere. www.indiandentalacademy.com
Inversions: A portion of the chromosome has broken off, turned upside down and reattached, therefore the genetic material is inverted. Rings: A portion of a chromosome has broken off and formed a circle or ring. This can happen with or without loss of genetic material. www.indiandentalacademy.com
Chromosome abnormalities can be inherited from a parent (such as a translocation) or be "de novo" (new to the individual). This is why chromosome studies are often performed on parents when a child is found to have an abnormality.
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Single gene mutations Disorders in this group are due to defects in a single gene which refers to a primary error in the DNA code. They are inherited following mendelian laws
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AUTOSOMAL DISORDERS
Classified as
X LINKED DIORDERS
MITOCHONDRIAL DISORDERS
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Multifactorial Certain disorders which appear to be common more common in related individuals have a complex etiology involving genetic as well environmental factors. In multifactorial inheritance there is experimental evidence to believe that several genes acting together (Polygenes) might be responsible for a given anomaly. The phenotype results from an interplay of genotype with enviornment. www.indiandentalacademy.com
Genetics and Craniofacial Syndromes. Holoprosencephaly: Malformation sequence in which impaired midline cleavage of the embryonic forebrain is the main feature. Associated facial anomalies in this syndrome include cyclopia, median cleft lip, lateral cleft lip. www.indiandentalacademy.com
A number of mutations in several genes have been identified as causative, of which the best known is Sonic Hedgehog (SHH). Other gene mutations involve TGIF, SIX3 .
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Craniosynostosis: Defined as the premature fusion of skull bones. It is found in association with a number of different disorders.e.g. Crouzon, Apert, Pfeiffer, Beare-Stevenson syndromes. Genetic etiology: Mutations in the Fibroblast Growth Factor Receptor (FGFR) genes with resultant gain of function, especially in FGFR2 have been identified in various craniosynostosis syndromes. Also chromosomal alterations leading to loss of function in the TWIST gene, are implicated
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Evaluation of craniosynostosis – Skull shape is best assessed from a “bird’s eye view”. Look for areas of flattening or prominence of the skull. CT scan is more accurate way of assessing patency of sutures. Head shape may be described as dolichocephalic, brachycephalic, or plagiocephalic. www.indiandentalacademy.com
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PLAGIOCEPHALY SCAPHOCEPHALY www.indiandentalacademy.com
Oral cavity should be assessed for integrity & characteristics of palate. Clefting can be seen, also a narrow high arched palate (“Byzantine” palate) as seen in Apert’s syndrome. Abnormalities of hand & feet can help to distinguish between different craniosynostosis syndromes which may have a similar facial appearance. www.indiandentalacademy.com
Cleft Lip & Palate Clefts of the lip and palate are the most common craniofacial birth defects and are among the most common of all birth defects. There is much evidence to support the view that genetic factors are associated with oro-facial clefting. Though clefts occur sporadically, some families have more than one individual affected with clefts. www.indiandentalacademy.com
A. Single gene etiologies: There are almost 300 syndromes which have a cleft of the lip and palate as a feature. Out of these, about 150 syndromes are due to Mendelian inheritance of alleles at a single genetic locus. About 50% : Autosomal recessive. 40% : Autosomal dominant 10% : X linked inheritance. www.indiandentalacademy.com
Some of the genes involved are – GL13 7p13 PAX3 2q35 SIX3 2p21 SOX9 COL2A1 etc www.indiandentalacademy.com
B. Chromosomal anomalies: Orofacial clefting is seen as part of phenotype in wide variety of chromosomal rearrangements, including trisomies, deletions, duplications, micro-deletions or cryptic rearrangements. E.g. deletion of 4p (Wolf-Hirschhorn Syndrome), 4q or 5p (Cri-du Chat syndrome) trisomy of 13 or 18, etc. Role of small rearrangements such as microdeletions, cryptic rearrangements in cleft etiology is important as they are often transmitted within families.
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Micro-deletion of 2q11.2 is now known to be the common etiology for three different syndromes with cleft of secondary palate as a frequent feature. DiGeorge Syndrome Velocardiofacial syndrome Conotruncal anomaly face syndrome. One reason for mapping and cloning genes for syndromic forms of clefting is to help develop strategies for delineating the etiology of nonsyndromic form of clefting, which is by far much more common. www.indiandentalacademy.com
C. Non-syndromic orofacial clefts: Early estimates of genetic contribution to non- syndromic orofacial clefts ranged from 12-20%, with remainder attributed to environmental factors. Recent studies estimate the genetic component to be much higher: 20-50%.
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Treacher Collins Syndrome(Mandibulofacial dyostosis) Problem arises because of altered neural crest development secondary to excessive cell death in trigeminal ganglion. Inheritance pattern – Autosomal dominant or sporadic. Genes – Treacher Collins Franceschetti syndrome 1 ( TCOF1). Craniofacial manifestations – Down slanting palpebral fissures, malar hypoplasia, mandibular hypoplasia, malformation of external ear, cleft palate.
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Severe micrognathia in some patients contributes to dental crowding. Gonial angle is more obtuse than normal, ramus may be deficient. Coronoid & condyloid process are flat or even aplastic. Frequently orthognathic surgery is required.
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Crouzon’s Syndrome Also known as craniofacial dysostosis. Inheritance pattern – Autosomal dominant. Gene – FGFR2. Characterized by cranial synostosis, ocular proptosis and hypoplastic maxilla. Cleft palate can also be seen. Syndrome arises because of prenatal fusion of the superior & posterior sutures of maxilla along the wall of orbit.
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Underdevelopment of middle third of face – responsible for relative mandibular prognathism. Characteristic protrusion of eyes is largely an illusion - the eyes appear to bulge outward as area beneath them is underdeveloped. When cranial sutures become synostosed, intracranial pressure increases. Cranium is usually brachycephalic. www.indiandentalacademy.com
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Diagnosis is made after distinguishing it from other types of premature cranial synostoses such as cleidocranial dysplasia , Apert syndrome. Surgery to release suture is necessary at an early age.
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Apert Syndrome Also called as Acrocephalosyndactyly. Mode of inheritance – Autosomal dominant. Gene – FGFR2. Characterized by high & prominent forehead, midface hypoplasia. Palate is typically high arched & narrow giving a ‘Byzantine’ arch appearance. There is severe & symmetric syndactyly of digits. www.indiandentalacademy.com
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Dermatologic conditions – Hyperhidrosis, oily skin & acneiform lesions are common. Also there is no saggital or metopic suture. They do not form at all. Incidence of mental deficiency is higher in patients. Early surgery for craniosynostosis is indicated.
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Crouzon Vs Apert Clinical findings in crouzon is generally limited to Head & neck region. Intelligence is usually normal in patients with crouzon’s syndrome.
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Hemifacial microsomia Condition is etiologically multifactorial. Many chromosomal abnormalities have been recorded. Environmental causes include administration of thalidomide, primidone, retinoic acid during pregnancy. Affects aural, oral & mandibular growth. May be mild or severe. Variant is GOLDENHAR SYNDROME – oculoauriculovertebral dysplasia. www.indiandentalacademy.com
Face may be strikingly asymmetrical because of hypoplastic changes in the mandible & dysplatic changes & displacement of ear. There is hypoplastic changes in the muscles of mastication, muscles of facial expression, lower facial weakness. 7% of reported patients have cleft lip / palate. Other features include mental deficiency, vertebral anomalies, CVS anomalies. www.indiandentalacademy.com
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If condition is mild ,child may respond to functional appliance therapy. Severe cases – Distraction osteogenesis is used to achieve large amount of mandibular lengthening.
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Ectodermal Dysplasia Inheritance pattern – X linked recessive, autosomal dominant, autosomal recessive. Genes – Ectodysplasin 1 , MSX 1, PAX 9. General manifestations – Sparse hair, dry skin, absence of sweat glands, normal mental status. Craniofacial manifestations – Small nose, hypodontia, conical or malformed teeth, deficient alveolar ridge, cleft lip & palate (severe form). www.indiandentalacademy.com
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Underdevelopment of alveolar ridges makes fabrication of denture much more challenging. Treatment include placing bone grafts due to reduced thickness and height of alveolar ridge. Followed by giving dentures / implants. Unerupted teeth can be brought in arch by orthodontic traction. When the teeth gets aligned in arch they can be helpful in support & stabilization of planned prosthetic work.
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Achondroplasia Inheritance pattern – Autosomal dominant. Gene – Mutation in FGFR. Recurrent muta-tions of a single amino acid in the transmembrane domain of the FGFR3 protein is the culprit. Manifestations include short stature and craniofacial malformations, including a short cranial base with early spheno-occipi-tal closure and megalocephaly. www.indiandentalacademy.com
Failure of cartilage proliferation leads to underdevelopment of mid face. Characteristic short arms and legs. Cephalometric changes include frontal bossing, short posterior cranial base, retrognathic maxilla, normal mandible & protruded maxillary incisors.
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Growth hormone treatment has shown to improve limb length in achondroblastic children. However cranial base reaches adult dimension by age 7, so hormone treatment had to begin very early to have any hope of decreasing maxillary deficiency. In older patients Lefort III osteotomy is done to move entire midface forward.
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Cleidocranial dysplasia Inheritance pattern – Autosomal dominant or new mutation. Gene – Runt related transcription factor 2 (RUNX2). General manifestations – Moderate short stature, normal intelligence, partial to complete absence of clavicles. Disturbances in the growth of the bones of the cranial vault, the maxilla, and the nasal and lachrymal bones. www.indiandentalacademy.com
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Dentoalveolar characteristics : 1. Over-retained deciduous teeth with unresorbed roots. 2. Supernumerary teeth that displace the developing permanent teeth and obstruct their eruption. 3. Retarded eruption because of a lessened eruptive potential, although it is not entirely absent. 4. Reduced height of the lower third of the face and a skeletal Class III tendency due to underdevelopment of the maxilla and to an upward and forward mandibular rotation. The vertical development of alveolar bone is markedly reduced, with a shallow buccal and lingual sulcus. www.indiandentalacademy.com
5. A late, but spontaneous eruption of first and, usually, second permanent molars in both jaws. 6. Serious (approximately 3 years) delay of the root development of the permanent teeth.
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Orthodontic Treatment Strategy
Space for the unerupted teeth is provided by anteroposterior expansion of the dental arches and, in the vertical plane, by the extraction of deciduous and supernumerary teeth. Both these measures may improve the chances for normal root development by maximizing any eruptive potential that the permanent teeth may possess, which may express itself to varying degrees.
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The fulfillment of the following conditions will make efficient orthodontic force application possible: a. A sufficient number of erupted anchor teeth. Typically, the permanent molars erupt quite normally and, in many cases, one or two incisors may also be present in each jaw. b. A rigid appliance frame. This is needed to withstand the distortion from oral function, considering the long spans of free, unattached, and unprotected arch wire, mesial to the few erupted anchor molar teeth. c. The application of light forces with a good range of action to individual and groups of unerupted teeth.
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The design of the appliance must take into account the need for it to be sufficiently versatile to carry out its three distinct tasks efficiently, namely, to apply forces in the vertical plane to resolve the multiple impactions, to adapt to the changing environment from a partial to a full permanent dentition, including reapportioning space for further unerupted teeth and establishing interproximal contacts and arch form, and to bring about an occlusion of these teeth, along with a corrective realignment of their long axes.
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RETENTION Vertical relapse of the extruded teeth does not occur after treatment and the use of fixed lingual arches provides good control of buccal expansion. Post treatment alteration of the arch width will not therefore occur. The correction of severely rotated teeth and the labiolingual positioning of the anterior teeth are the most challenging aspects of therapy. www.indiandentalacademy.com
It would be inappropriate to determine labiolingual incisor position in patients with cleidocranial dysplasia from existing cephalometric tables of normal persons. Clinical judgement must be exercised by the orthodontist in the final decision, and long-term retention of the result is advised.
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It is good to place these teeth well forward, with the incisal edges below the level of the upper lip, overcompensating for the prolonged period of relative edentulousness incurred by the patient. The use of bonded multistrand wire retainers is recommended from canine to canine in both jaws to hold this position and to prevent rotational relapse. www.indiandentalacademy.com
Orofacial digital syndrome Term designates a group of heterogenous clinical patterns of which 9 different subtypes have been described. X linked condition characterized by oral,facial & digital malformations. Facial features – frontal bossing, ocular hypertelorism, short upper lip with cleft. Digital features – Syndactyly, brachydactyly, polydactyly. www.indiandentalacademy.com
Oral features – midline cleft lip & palate, tongue shows furcation, mandible is small in size, supernumerary canines & premolars are common. Valiathan et al (OOOE , 2006,inpress) have reported a case of orofacial digital syndrome type V known as THURSTON SYNDROME.
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Patient who is a 13yr old south Indian boy presented with features of incomplete median cleft of upper lip & polydactyly of both hands & left foot. Family history revealed his two elder sisters having a similar deformity of hands, toes. Intraoral examination showed a high arched palate, upper right central incisor exhibited 90 Ëš distolingual rotation. Both maxillary canines were retained, permanent left maxillary canine was missing. www.indiandentalacademy.com
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Mandibular dental arch was normal & well aligned. Angles class I malocclusion with deep overbite & 7mm overjet was evident. Orthodontic treatment was started with 0.022X0.028 inch edgewise appliance with cervical pull headgear for alignment of teeth & to reduce deep bite. www.indiandentalacademy.com
Ehler Danlos Syndrome Group of heterogeneous inheritable connective tissue diseases. The apparent cause is a genetic defect causing an error in collagen synthesis or processing. It was the first heritable disorder of collagen that was elucidated at the biochemical level. Currently, nine separate and distinct forms are recognized. www.indiandentalacademy.com
They share cardinal features of joint hypermobility and hyperextensibility, plus fragility and tendency toward bruising of the connective tissues, grossly characterized as excessive elasticity of the skin and laxity of the joints. Able to touch the tip of the nose with their tongue. These patients have excessively stretchable and, occasionally, floppy ears. Their eyelids evert easily. www.indiandentalacademy.com
The joints of people with EDS are characterized as hypermobile. Subluxation and dislocation are recurring problems.
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An orthodontic appliance for a patient with EDS should be smooth and relatively simple in spring design, so that the tongue and buccal mucosa are not abraded. Because of the cross-link defect in collagen, it can be expected that for a given moment-to-force ratio, as applied for tooth movement, the periodontal ligament of a patient with EDS may show a larger strain than that of a normal child. www.indiandentalacademy.com
With the added dental mobility of the teeth, slowed repair processes, and poor organization of periodontal collagen, retention after completion of the case may be longer. Although anatomic defects in root structure have been described in patients with EDS, the molecular composition of the dentin has not been studied. If changes do exist, root resorption could be a problem.
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Osteogenesis imperfecta Inheritance pattern – Autosomal dominant or sporadic. Gene – Mutation in genes COL1A1, COL1A2 that encode for type 1 collagen. General manifestations – Bone fragility, short stature, hyperextensible joints, deformity of limbs. Craniofacial / dental manifestations – Triangular facies, blue sclera, occasional dentinogenesis imperfecta ( seen in Type IV), delayed eruption of teeth. www.indiandentalacademy.com
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75% of adult patients exhibit class III malocclusion. Risks in treatment – a) Because of chances of enamel fracture, bonding of brackets although not contraindicated has to be thought about – BANDING can be done. b) Surgical treatment to correct class III malocclusion has inherent risks of excessive hemorrhage, bone fragility, difficulty in intubation. www.indiandentalacademy.com
Dentinogenesis imperfecta Inheritance pattern – Autosomal dominant or sporadic. Gene – Dentin sialophosphoprotein (DSPP). Primary & permanent dentition are affected, teeth are blue gray / brown, susceptible to extreme wear, pulpal obliteration, dental abscesses. Restorative procedures need to be undertaken.
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Amelogenesis imperfecta Inheritance pattern – Autosomal dominant, autosomal recesive, X linked, sporadic. Genes – Amelogenin, enamelin. Affects both dentitions, teeth appearance is yellow brown to orange. Teeth are sensitive, susceptible to wear. Combination of veneers and full coverage cast crowns are used to prevent wear. www.indiandentalacademy.com
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Trisomy Syndromes A) Trisomy 21 ( Downs Syndrome) – Autosomal chromosome disorder. Condition arises as a result of zygote with 3 chromosomes of number 21 instead of 2. Affected individual is mentally retarded, short statured, exhibit brachycephaly. Fontanelles close later. Dental manifestations – Short mouth, large tongue, tongue thrust, maxillary lateral incisor show abnormality, microdontia, delayed eruption, palate is high arched & narrow. www.indiandentalacademy.com
More susceptible to periodontal disease. B) Trisomy 18 ( Edwards syndrome) – Affected individuals are mentally retarded. Prominent occiput, small eyes, micrognathia, high arched palate, occasional cleft palate & bifid uvula.
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Turner Syndrome Also called XO syndrome. One X chromosome is missing. Characterized by short stature, sexual infantalism, & often renal & gonodal disorders. The most typical oral characteristics reported have been a high palate and a small mandible or even a hypoplastic mandible. Teeth may erupt prematurely. www.indiandentalacademy.com
It has been established that the rate of any growth spurt is below normal and changes are minimal during puberty or that there is delayed growth, which is accentuated in comparison with the normal population
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Morquio syndrome Inheritance pattern – Autosomal recessive. Genetic disorder characterized by lack of galactosamine 6 sulfatase activity. Characterized by short stature,short neck, corneal opacities, muscle weakness, deafness. In dentoorofacial area it is characterized by a flat nasal bridge, broad mouth, labially inclined upper incisor,spaced arch, thin enamel. www.indiandentalacademy.com
Tsuyoshi et al ( Angle 2005) reported a case with morquio syndrome showing characteristic features. Patient was 7 yr old girl. She showed Skeletal & dental class I malocclusion with spacing in both arches. She had tongue thrusting habit also. Initially a removable appliance to control tongue thrust was given following which spaces were closed with fixed mechanotherapy. www.indiandentalacademy.com
Conclusion Genetic Engineering has opened a new approach to the diagnosis, prevention, and control of diseases and malformations. Technique of genetic engineering include amniocentesis, chromosome karyotyping, recognition of chromosome aberrations & their relation to specific dentofacial anomalies & malocclusion, the aborting of harmful genes & introduction of desirable genes into early forming embryo. www.indiandentalacademy.com
These techniques eventually will make possible the prevention of many antenatal, congenital genetically induced dentofacial anomalies including dental malocclusion. At present if the problem is genetic, orthodontists are limited in what they can do or change.
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References Ashima Valiathan, Sivakumar A, David M., Manna Valiathan , Satyamoorthy : Thurston Syndrome – Report of a new case. OOOE (In press). Tsuyoshi Kuratani, Shouichi Miyawaki, Takashi Murakami : Early orthodontic treatment and long term observation in a patient with Morquio syndrome. Angle Orthodontist 2005;75 (5);881 – 887. J.Kindelan, M.Tobin, R.A.Loukota: Orthodontic & orthognathic management of a patient with osteogenesis imperfecta & dentinogenesis imperfecta. J.O. 2003,(30) ; 291 -296.
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