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Environmental Disease
Published in Gary S. Moore, Kathleen A. Bell, Living with the Earth, 2018
Gary S. Moore, Kathleen A. Bell
Other genetic diseases are inherited as autosomal recessive, which means that a defective gene must occur in both chromosomes at complementary sites in order for the disease to be expressed. It also means that both parents, if healthy, were each carriers of the defective gene, which they passed along to the child. A person with this type of genetic disease is deprived of an essential protein resulting in a potentially severe disease, such as PKU or CF.27 There are also dominant and recessive defective genes on the sex chromosomes as well, producing a variety of sex-linked diseases, including hemophilia-A, color blindness, and forms of muscular dystrophy. Since males have one copy of the Y-chromosome, even recessive sex-linked genetic diseases are expressed in men, as there is no other allele to mask the defect.
Gene Editing: A View Through the Prism of Inherited Metabolic Disorders
Published in The New Bioethics, 2018
The inherited metabolic disorders arise when a mutation in a given gene results in a deficiency of the related enzyme. The majority of these conditions are inherited in an autosomal recessive manner, whereby both the maternally inherited and paternally inherited copy of the given gene must harbour a mutation for the disease to manifest. In the usual situation this means that both parents are heterozygous carriers of the condition, i.e. they each carry one mutated copy of the gene and one ‘healthy’ copy. Thus a deficiency of the enzyme phenylalanine hydroxylase caused by mutations in the PAH gene gives rise to the condition phenylketonuria (PKU), associated with pathologically high phenylalanine levels as this amino acid cannot be converted to tyrosine. Untreated, PKU results in significant progressive damage to the central nervous system, manifesting with microcephaly, developmental delay and significant cognitive impairment. PKU is eminently treatable with dietary phenylalanine restriction, and detection via newborn screening permits treatment to be commenced before damage occurs. Many of the metabolic disorders, however, carry a devastating prognosis, for example mucopolysaccharidosis type III (Sanfilippo syndrome) which is caused by deficiency of one of the several lysosomal enzymes that degrade complex macro-molecules (the glycosaminoglycans), with the result that these macro-molecules accumulate in different tissues of the body including the brain and cause a relentlessly progressive neurodegenerative disorder, with childhood onset dementia and significantly curtailed life-expectancy.