Genetic technology applied to medicine

Biology A2 · Genetic technology. The idea in plain words, the rules to remember, the mistake to avoid and a worked example, written and checked by Mega Lecture.

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The idea

Genetic technology helps medicine in three ways. First, human proteins can be made by genetically modified cells. These recombinant proteins, such as insulin, factor VIII and adenosine deaminase (ADA), are identical to the human protein, can be made in large amounts and carry no risk of infection from animal tissue or donated blood.

Second, genetic screening tests a person's DNA for particular alleles. People who know their result can make choices about treatment and about having children.

Third, gene therapy puts a normal allele into the cells of a person with a genetic disease, using a vector such as a virus. It has been used for SCID and for inherited eye diseases.

Rules to remember

Recombinant insulin treats diabetes; factor VIII treats haemophilia; ADA treats one form of SCID.
BRCA1 and BRCA2: mutant alleles raise the risk of breast cancer; a carrier can choose extra checks or preventive surgery.
Huntington's disease is caused by a dominant allele and appears in middle age; a test allows a person to plan ahead.
Cystic fibrosis is recessive; screening finds carriers, and two carriers have a 1 in 4 chance of an affected child each time.
SCID gene therapy: stem cells are taken from the patient, given a working ADA gene by a vector, and returned.
Eye disease: the vector carrying the normal allele is injected into the retina, which is easy to reach.
Somatic gene therapy changes body cells only, so it is not inherited; germ-line therapy would be passed to later generations.

Common mistake

Students say that gene therapy removes or repairs the faulty allele. In these treatments a working allele is added to some cells; the faulty one is still there, and the gametes are unchanged.

Worked example

A woman is tested and has one allele for Huntington's disease. Her partner does not have the allele. What is the chance that their first child inherits it, and why is this different from cystic fibrosis?

Huntington's is caused by a dominant allele, so she is heterozygous: one Huntington's allele and one normal allele.
Half of her eggs carry the Huntington's allele; all of her partner's sperm carry the normal allele.
So the chance for each child is 1 in 2, and a child with the allele will develop the disease.
Cystic fibrosis is recessive, so a child must inherit the allele from both parents.

Answer: 1 in 2 (50%) for each child.

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