AUTOSOMAL DISORDERS
GENETICS IN PEDIATRIC DENTISTRYCommon chromosomal Syndromesin ChildrenSyndromeDown'ssyndromeEtiologyTrisomy of21st chromosomeCraniofacial features Flat face
Large anterior fontanelle
Open sutures
Small slanting eyes withepicanthal folds
Open mouth
Frequent prognathism
Macroglossia
Fissured or pebbley tongue
High arched palate
Malformed teeth
Decreased cariesOther features Sexual underdevelopment
Cardiac abnormalities
Hypermobility of joints
Mentally retarded
SyndromeKlinefeltersyndromeEtiologyExtra Xchromosomein malesCraniofacial featuresTaurodontism
Other featuresRelatively short limbsSyndromeTurner's syndromeEtiologyMissing XchromosomeCraniofacial featuresHeart-shaped facies
Prominent ears
Webbing of posterior neck
Low posterior hairline
Other features Congenital lymphedema
Broad chest
HypogonadismAUTOSOMAL DISORDERS
Autosomal dominant disordersAutosomal recessive disordersAutosomal dominant disordersarise due to defect in atleast one gene out of a pair of genes on autosomes.
Features
Disease usually appears in each generation Delayed age of onset Vertically transmitted Affected individual has an affected parent Male and female siblings are equally affected Capability of transmission is same in both the affected parents
Examples
Osteogenesis imperfecta, mesiodens, Hypocalcified type I Hereditary Dentinogenesis imperfecta,Dentin dysplasia (Radicular type), Apert's syndromeAutosomal recessive disordersoccur when both thegenes on autosomes are affected. Features
The illness usually appears suddenly in the family Males and females are equally affected Early age of onset Most of the offsprings are normal in the family An affected offspring mayor may not have an affected parentExamples
Dentin dysplasia (coronal type), hereditary amelogenesis imperfecta (hypocalcified type II), hypoPhosphatasia,Hurler's syndrome
Genetic CounsellingA genetic counselor must have:I. Precise and fully confirmed diagnosis of the disease2. Accurate pedigree of the family3. Knowledge of the mode of inheritance of the conditionINDICATIONS FOR PRENATAL DIAGNOSIS
I. Advanced maternal age (e.g., Down's syndrome)2. Previous child with chromosome aberration3. Congenital anomaly4. Structural anomalies found on ultrasonography5. Person with mental retardation or developmental delay
PROCEDURES FOR PRENATAL DIAGNOSISVisualization of Fetus
Ultrasonography: With this technique it is now possibleto visualize the embryo as early as 51/2 to 6 weeks of pregnancy and cardiac activity is detectable at 7-8weeks.Radiography can also be done2. Analysis of Fetal Tissue
AmniocentesisChorionic villus samplingAmniocentesis (Optimum time: 16-18 weeks of gestation):
Under strict aseptic conditions and localanesthesia, 20-30 ml of fluid is aspirated.
About 90% of all amniocentesis are performed for cytogeneticanalysis. The rest 10% is used for biochemicalinvestigation.
The fibroblast-like cells obtained atAmniocentesis. A minimum of 15 cells are examinedand the modal chromosome number is established.Sex determination of fetus is 99% accurate by thismethod.Chorionic villus sampling (optimal time 9-12 weeks)10-25 mg of chorionic villi iscollected. Because the Langerhans cells of the cytotrophoblastare in dividing phase, it is possible to performa "direct" chromosome analysis, immediately after sampling,or alternately after 24 hours of incubation in atissue culture medium. OTHER TESTSFetal and maternal blood analysis non-invasive prenatal diagnosis.
Fetal liver biopsyFetal skin biopsyGENETICS IN PREVENTION OF DENTALCARIESGenetic Engineering in Dental Caries
S mutans has been genetically modified, lacking the specific gene codes for theenzymes necessary to produce decay. These modifiedstrains are being incorporated in daily use eatables likeapple, milk, yoghurt.Recent Discoveries
1. Recently a vaccine has been discovered, a protein called p1025. This protein tricks S mutans leaving no vacant sites for its attachment on tooth.
2. Robert Buine (2000) had developed strains of S mutans that are endowed with a gene to increase production of urease which creates basic conditions conducive to remineralisation.
3. Replacement Therapy: A harmless effector strain is permanently implanted in the host's microflora.
Biomimetic Materials
Genetically engineered materials are under the trialwhich may mimic the nature of tooth substance and helpto regenerate the dental tissue. STEM CELLSTwo properties which must be satisfied for a cell to bedefined as a stem cell are:
Self-renewal Multi-lineage differentiationStem cells can be classified as:
Embryonic or fetal stem cells
Postnatal or adult stem cellsDental Applications of Stem CellsDental Pulp Stem Cells (DPSC)DPSCs are the stem cells which have the ability to regeneratethe dentin-pulp complex.Stem Cells from Human Exfoliated Primary Teeth(SHED)
The stem cells from human exfoliated primary teeth havebeen identified to form part of highly proliferative,clonogenic cell capable of differentiating into variety of cells types including neural cells, adipocytes, andodontoblasts.
The DPSCs and SHED are being utilized to a greatextent in regenerative endodontics.
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