Biol 121 225
Freeman 390-395, 407-411, 417-424 Mar. 3, 10
Ch. 19, Gene Technology
Pituitary dwarfism and growth -people with pituitary dwarfism have defective copies of the gene GH1 which
hormone codes for the GH1 growth hormone protein
-affected people are typically no more than 4 feet tall by adulthood
-growth hormone was injected into people just like insulin injections for diabetes
-only growth hormone from humans worked, and therefore it had to be extracted
from cadavers (dead bodies) and therefore was scarce/expensive
-even worse, infectious proteins called prions that cause degenerative brain
disorders emerged in patients – people can get prions by inheritance or by eating
-their growth hormone supply was contaminated with a prion protein from the
brains of the cadavers supplying the hormone
Retroviruses -retroviruses are currently the vector of choice in gene therapy
-they are viruses that have an RNA genome and can code for proteins that produce
DNA from their RNA and insert it into the DNA of the cell
-however, viruses usually cause disease and even when inactivated, altered
particles may be able to recombine with viral DNA that already exists in the
individual being treated and lead to the formation of a new infectious strain
Method of introducing alleles into 1. Engineered retrovirus has recombinant RNA containing viral and human
human cells using engineered viruses sequences.
(4 steps) 2. Recombinant genes enter host cell.
3. Viral enzymes make double-stranded DNA version of introduced genes (reverse
4. Recombinant genes are inserted into host chromosome and transcribed.
SCID -severe combined immunodeficiency
-lack normal immune system, cannot fight off infections
-“the boy in the bubble”
-defective gene for receptor protein necessary for development of T cells
Gene therapy with SCID (3 steps) 1. Stem cells are isolated from the patient’s bone marrow and grown in vitro.
2. Recombinant retroviruses carry the normal allele into host cells.
3. Cells that are expressing normal alleles are isolated and implanted into patient.
Problems with this -two of the ten boys they initially treated developed cancer characterized by
unchecked growth of T cells
-a viral-borne receptor gene had been inserted near the gene for a regulatory
transcription factor that triggers growth of T cells – cancer