Larger than Life. Angela Thomae Case Study CHEM 454

Transcription

1 Angela Thomae Case Study CHEM 454 Larger than Life Maria Thomas, a 5 year old girl, was brought to Urgent Care at the hospital because of a painful swelling in her neck. The doctor who was on call that night, Dr. Anton, quickly diagnosed it as swelling of the neck lymph nodes, a common side effect of a bacterial infection. He took a throat culture, and told Mrs. Thomas to take Maria home, and that someone would call with the results. The next day, Dr. Anton s nurse called Maria s house and told Mrs. Thomas that the throat culture was negative for a strep infection. The nurse explained that it was probably a viral infection, and that Maria should just wait it out with liquids and lots of rest. One week later, Maria was brought back into Urgent Care. The swelling in her lymph nodes had gotten worse; her neck was enlarged to twice the normal size. Her skin was showing a slight yellowish color. She was also showing signs of listlessness and fatigue, and her heartbeat was more rapid than usual. Dr. Anton was called in, and concerned with her newest symptoms and that the swelling had not gone away, referred Maria to an oncologist, Dr. Stevens. Dr. Anton also did a quick exam, and took a blood sample for lab analysis. The lab showed Maria was severely anemic; her blood hemoglobin was only 6.5 mg/dl, much lower than the normal female level of 12-15mg/dL. Her total bilirubin was 2.4 mg/dl, higher than the normal bilirubin count of mg/dl. Her pulse, at 125 beats/min, was also high for a 5 year old girl (normal pediatric rate is bpm). That next week, Maria was admitted to the hospital and a biopsy was performed on her neck. Mrs. Thomas was relieved to hear her daughter did not have malignant lymphoma; the biopsy was negative. While an abnormal number of lymphocytes were present in her lymph nodes, none of them were cancerous. Puzzled, Dr. Stevens ordered an HIV screen to see if Maria was experiencing opportunistic viral infection and went to grab some coffee, anticipating a long night. In the break room, she ran into her friend and colleague Dr. Andry, an immunologist who worked in the lab. Making small talk, Dr. Stevens told Dr. Andry about Maria. Dr. Andry asked if she could examine Maria s chart.

2 Thomas, Maria. Female, Age 5: DOB 11/06/95 5/12/00 Slight lymphadenopathy. Strep culture: negative Dr. Anton Polaroid of Maria s lymph node enlargement. From Blood, vol 89, /20/00 Severe lymphadenopathy Dr. Anton Listless, fatigued Jaundice Pulse: 125 beats/min (high) BP: 94/56 (normal) Blood labs-- Hemoglobin: 6.5 mg/dl (low) Significant amount of red blood cell debris from hemolysis Total bilirubin: 2.4 mg/dl (high) 5/27/00 Biopsy: negative Dr. Stevens Analysis of lymph nodes: (From American Journal of Pathology, vol 153, 1998) Histopathology of lymph nodes: markedly expanded by lymphocytes Para cortex populated by lymphocytes, plasma cells, and immunoblasts

3 Dr. Andry decided to run an apoptotic assay on Maria s lymphocytes that were taken from the biopsy. The cells were incubated with and without an apoptotic stimulus, and then propidium iodide was used to mark nonviable cells. The assay showed a significant decrease in lymphocyte cell death, much less than the normal controls. Tables from Blood, vol. 89, % Cell Loss Maria Thomas 13 Normal control 87 Encouraged by this, she did an immunologic profile of Maria s serum. Serum Igs (mg/dl) IgM IgG IgA Maria Thomas Normal control Meanwhile, the HIV test came back negative. Dr. Stevens was thoroughly frustrated by the time Dr. Andry knocked on her door and said she knew just what was wrong. 1.) What is the cause of Maria s symptoms (what disease does she have)? a. What are the two genes in which mutations can cause this defect? b. What are some common amino acid mutations? 2.) What does this defect do to the apoptotic pathway? 3.) What is causing Maria s anemia? Her jaundice? 4.) Why does she have abnormal levels of immunoglobulins? 5.) How would this disease be treated?

4 Solution: Maria is suffering from a genetic disorder called ALPS (autoimmune lymphoproliferative syndrome). It is an autosomal dominant mutation in either the Fas (CD95) or Fas ligand (CD95L) genes. Fas and Fas ligand play a very important role in apoptosis, or programmed cell death. Lymphocytes, as part of the immune system, are constantly dividing when presented with an antigen. Apoptosis is critical to maintaining the homeostasis of lymphocytes through a signaling pathway. The Fas interaction with its ligand sends a signal through to the death domain, a cytoplasmic region of Fas, which recruits FADD, a signal protein. The binding of FADD to the death domain of Fas initiates the cleavage of a procaspase to an active caspase, which leads to apoptosis through proteolytic events. Without Fas or Fas ligand, the apoptotic pathway is not finished because the signal is not created properly, leading to an accumulation of B and T lymphocytes in lymph nodes and spleen. Some common amino acid mutations of the Fas death domain are: Thr-225 to Pro, Leu-278 to stop codon, Arg-234 to Pro, and Asp-244 to Val. Sequencing of Maria s DNA indeed showed a mutation in Fas. As a result of the excess lymphocytes, it is common in ALPS patients to have a higher amount of antibodies circulating in the blood, which leads to autoimmune disease. Anemia is commonly seen due to hemolysis of red blood cells; for Maria it is the result of her own antibodies attacking her red blood cells. It is common to see autoimmune attacks on kidneys, neutrophils, platelets, and phospholipids in ALPS patients. A side effect of hemolysis is bilirubin, which causes jaundice when it builds up from breakdown of heme groups (bilirubin is a yellowish color). While ALPS is an autosomal dominant genetic defect, it is obvious that there are other factors. If it is not a de novo mutation, then Maria s mother or father must be a carrier, yet neither of them shows any symptoms. Familial studies of ALPS patients and their families show that it is common for a family member to have the Fas or Fas ligand mutation and not present any symptoms. There is no cure for ALPS currently, but it can be treated. Treatment with prednisone drastically reduces swelling of lymph nodes, although not completely to normal levels. Systemic corticosteroid therapy treats severe hemolytic anemia. Interferon-alpha, IL-2, and cyclosporin can treat lymphoproliferative disease.

5 References Autoimmune Lymphoproliferative Syndrome; ALPS # [On-line]. Available [2001, March 31]. Lim, Megan, and Straus, Stephen et. al. (1998). Pathological findings in human autoimmune lymphoproliferative syndrome. American Journal of Pathology, 153, Martin, David, and Zheng, Lixin et. al. (1999). Defective CD95/APO-1/Fas signal complex formation in the human autoimmune lymphoproliferative syndrome, type Ia. Proceedings of the National Academy of Sciences of the United States of America, 96(8), Sneller, Michael and Wang, Jin et. al. (1997). Clinical, immunologic, and genetic features of an autoimmune lymphoproliferative syndrome associated with abnormal lymphocyte apoptosis. Blood, 89(4), WebMd. (2000). [On-line]. Available