الفهرس 
IntroductionOnly 14 pages are availabe for public view
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Abstract
A short review has been given on the basic principles of genetics, which start by structure of human gene, how gene expression is regulated, and how it is transcribed and translated. The triplet basis of the gene code has also been reviewed noting the alterations or changes in the genetic material and nucleotides can result in mutations. Mention has been given on the mutagens and mutagenesis, which can arise as spontaneous mutations due to errors in the chromosomal divisions or DNA replication, or can arise
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through exposure to different enviro~ental agents.
The work defined gene therapy as being the transfer of recombinant DNA, transiently or permanently, into human cells for correction of disease. Gene therapy is classified into germ line gene therapy (involves genetically modifying a fertilized egg) and Somatic cell gene therapy (involves the genetic modification of any cells in a patient’s body apart from the reproductive cells).
Gene delivery is the process of introducing foreign DNA into host cells. Generally, the methods can be divided into two categories, viral
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(Retroviral vectors, Adenoviruses, Adeno-associated virus) and non-viral
(liposomes, plasmid, DNA Conjugates).
The genetic disorder can be caused by a problem in one or more of the genes. Genetic disorders may be classified into one of four types: single gene disorders, chromosome disorders, multifactorial disorders and mitochondrial disorders.
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()ufl’)fl’)0ry and (onclu\;ion)
The mam subject of this essay IS directed to discuss th;e genetic oisorders in head and neck which are:
I-Cystic fibrosis is a disease of exocrine gland function that involves multiple organ systems. It should be possible to treat cystic fibrosis with insertion of one copy of normally functioning DNA into the affected cells, independent of the class of mutation the recipient had before gene therapy.
2- Cleft Lip and Palate are birth defects arising from the interplay of multiple genetic and environmental factors. One gene contributing to
isolated cleft lip or palate, MSXI, has been id<yntified. . ;.
3- Thyroid Carcinoma, Medullary thyroid carcinoma is a neoplasm of the parafollicular C cells of the thyroid gland.
4-Salivary Gland Neoplasms, Many studies have investigated the role that tumor suppressor genes, especially the p53 family, play in the development of salivary gland neoplasms.
5-Acoustic neuromas are benign tumors that originate from Schwarm cells surrounding the vestibular nerve, usually within the internal auditory Congenital Hearin.