Hope... Page 6

The Journal: 1992

We have learned through Dr. Puck's test that two of our daughters are carriers of the defective gene. In our family, males will have a 50/50 chance of inheriting the abnormal X Chromosome that causes immune deficiency. Dr. Puck continues to use our family "genetic material" in her research, and hopes to use it to clone the SCID gene within the next two years. If she is successful, our family will have helped to make a significant advance in the fight against this killer.

Research Notes

In 1993 two laboratories, one of which was Dr. Puck's, identified the gene that is mutated to cause X-linked SCID. The gene is called IL2RG, which stands for interleukin-2 receptor gamma chain, and it encodes a protein that is expressed on the surface of normal T-cells and B-cells. The function of the protein is to receive signals for growth and activation (these signals are delivered by chemical lymphocyte hormones, or "interleukins"). When the receptor for these signals is disabled by a mutation in IL2RG, T-cells and B-cells cannot develop and function as they should, and SCID is the result.

The instructions for making the receptor are contained in 1400 bases, or letters of genetic code, on the X chromosome of all humans. The specific mutation in Mark Kent Anderson's IL2RG DNA was found by Dr. Puck to be a single letter of the genetic code changed from the normal "G" to an "A." This information made it possible for Dr. Puck's laboratory to look for the specific mutation in future pregnancies of the Upshaw family.

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This figure illustrates the results of a biochemical analysis of the genetic material in cells collected from Dr. Upshaw (sample on the far right), her daughter Ainsley (two samples in the middle) and grandson, Mark (sample on the far left). note the changing pattern of chemical bases in black bands (dark lines) under the "letters" G (for Guanine) and A (for Adenine). This indicates that from right to left (Dr. Upshaw to Mark), the mutation appears in Mark by a substitution of G to A (reduced number of dark lines under G). A normal, non-carrier cell (Non-SCID X hybrid) does not have a significant band under A, just under G. The G/A condition appears in the carriers, Dr. Upshaw and Ainsley. Figure used by permission from Puck et al., Human Molecular Genetics, 1993, Vol.2, No.8.

Just after publishing her first paper about the SCID gene in 1993, Dr. Puck moved to the National Institutes of Health in Washington, D.C. There she continues to do research on genetic disorders of the immune system, including SCID, at the National Center for Human Genome Research.

In early 1995 Dr. Howard Rosenblatt, a pediatric immunologist in Houston, traveled to work for two and a half weeks with Dr. Puck. Dr. Puck successfully cloned the SCID gene from the Upshaw family in 1993 and developed a way to diagnose the condition in utero. The treatment protocol which Dr. Rebecca Buckley successfully implemented at Duke Medical Center now offered hope for SCID infants for whom an identical or perfect marrow match could not be found.

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