Charge Syndrome - Essay Example

Charge syndrome is a rare condition experienced during foetus development affecting many organ systems. Children suffering from this condition have characteristics of asymmetric facial nerve palsy, blind-ending food pipe, and cleft lip. The Charge Syndrome is derived from the following disorders: coloboma (defects of the cranial nerve), heart defects, atresia of the choanae (blockage of the nasal breathing passages, growth retardation, and development, genital underdevelopment, abnormalities of the ear and sensorineural hearing loss. The Charge Syndrome is caused by diversification in CHD7 gene or and rarely does it occur, alteration genomic in the chromosome 8 regions where CHD7 gene is situated. CHD7 gene is vital in the formation of the retina as well as the cranial motor neurons (Blake & Prasad, 2006). Over 90% of the Charge victims have mutations in the CHD7 gene whereas 65%-70% of all suspected and typical cases combined are demonstrated CHD7 mutations. Pathogenic missense mutations are identifiable in the middle of the CHD7 gene while the benign variants are usually contained in the 5 and 3 parts. (Blake & Prasad 2006).

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The genetic contribution to medical practice is categorized in some divisions. The first category is made up of monogenic disorders of which include: Down syndrome, sickle cell anemia, phenylketonuria, and neurofibromatosis. It is a domain of medical genetics of which plays a big role in the care of individuals acquiring these disorders in ways like counseling, management and in diagnosis (Davenport, Hefner & Mitchell, 2009). The second category entails of more common disorders in which the substantial subset of individuals who are affected is caused by monogenic factors. Some of these disorders include colon cancer, hemochromatosis, cardiomyopathy, breast cancer and ovarian cancer. These disorders tend to have a penetrance that is age-dependent and an incomplete one.

Genetically inherited traits are those that are acquired from parents to their offspring of which occurs through sexual or asexual reproduction. In Charge Syndrome, the genetically inherited traits are of different types. Some of the traits include autosomal disorders, x- linked dominance, and recessive dominance (Jongmans, et al. 2006). In autosomal disorders, the gene inheritance can be of two types including autosomal dominant disorders and autosomal recessive disorders. The autosomal dominant disorders occur when the mutated gene displays itself as an autosome, and the victim requires only one of it to acquire the disorder. Both genders are likely to inherit the genetic mutation and get affected by it in equal proportion. The children of an affected victim are at high risk of inheriting the disorder.

In autosomal recessive disorders, the mutated gene occurs on the autosome although the victim requires two copies of each parents gene to be affected by the disorder (Verloes & Sanlaville, 2005). There is a high possibility too of the victim passing the disorder to his siblings. Incase both parents of an infant carry the genetic mutation of an autosomal recessive disorder, there is a 25% occurrence of the child inheriting both mutations and acquiring the disorder, a 50% occurrence of inheriting one copy of the mutated gene and a 25% chance of not getting affected by the mutation at all (Tellier et al., 2015).

In X- linked recessive disorders, the mutated gene happens to the X (female) chromosome. Males usually have one X and Y chromosome hence a mutated gene only on the X chromosome is valid to cause the disorder on its own. As for the case of females, one X-chromosome has less effect on a mutated gene since the females have two X chromosomes hence there is a non-mutation of the copy of the same gene (Sanlaville, & Verloes, 2007). A female who occurs to having one X chromosome is a carrier meaning on average 50% of her sons will acquire an inheritance of the mutation to develop the disorder whereas 50% of her daughters will acquire the inheritance of the mutation to become a carrier.

Penetrance refers to the percentage of people with mutation in a specific gene showing signs and symptoms of the genetic dysfunction. Where a patient does not exhibit features of the disorder is said to possess reduced or incomplete penetrance. For the complete penetrance not only does the major gene cause a phenotypic effect but also a recessive gene does during its homozygous state. Charge disorder exhibits reduced penetration as it is caused by environmental, lifestyle and genetic disorders. Variable expressivity is the variation of signs and symptoms occurring to different people with a similar genetic condition. The gene causes different variations in signs and symptoms for different individuals depending on the genetic condition. Since charge disorder is a genetic condition, it can affect all ages and sexes since at some point it may be recessive thus can be passed to anyone in the next generation.

References

Blake, K. D., & Prasad, C. (2006). CHARGE syndrome. Orphanet journal of rare diseases, 1(1), 34.

Jongmans, M. C. J., Admiraal, R. J., Van Der Donk, K. P., Vissers, L. E. L. M., Baas, A. F., Kapusta, L., ... & Van Kessel, A. G. (2006). CHARGE syndrome: the phenotypic spectrum of mutations in the CHD7 gene. Journal of medical genetics, 43(4), 306-314.

Sanlaville, D., & Verloes, A. (2007). CHARGE syndrome: an update. European Journal of Human Genetics, 15(4), 389-399.

Sanlaville, D., Etchevers, H. C., Gonzales, M., Martinovic, J., Clement-Ziza, M., Delezoide, A. L., ... & Audollent, S. (2006). Phenotypic spectrum of CHARGE syndrome in fetuses with CHD7 truncating mutations correlates with expression during human development. Journal of medical genetics, 43(3), 211-317.

Tellier, A. L., CormierDaire, V., Abadie, V., Amiel, J., Sigaudy, S., Bonnet, D., ... & Jan, D. (2005). CHARGE syndrome: report of 47 cases and review. American journal of medical genetics, 76(5), 402-409.