Clinical, Immunological and Genetic Analyses of ALPS

National Institute Of Allergy And Infectious Diseases

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Abstract

Research accomplishments of this project include: 1) This project allows us to study the largest cohort of patients with ALPS, one of the first genetic disorders of immunedysregulation. ALPS natural history study based on follow up of these patients over 20 yeas has been completed and a manuscript summarizing the critical features of the clinical and molecular pathogenesis in 150 patients with ALPS-FAS with a median followup of 13 years has been published as a plenary paper in an eminent hematological journal this year (Blood. 2014 Mar 27;123(13):1989-99). This included the validation of novel biomarkers of disease activity such as increased serum Vitamin B12 levels as well as establishing new modes of treatment for the disorder. Study of ALPS has elucidated the role of fas mediated apoptosis in lymphocyte homeostasis and lymphoma genesis. 2)This project has also led to identifying new genetic causes of ALPS like disorders by identification of mutations affecting RAS pathway in 14 patients, otherwise known as Ras Associated Leukoproliferative Disorder (RALD) : RALD: Patients with this ALPS like syndrome caused by somatic mutations in NRAS and KRAS are currently classified separately as ALPS related apoptosis disorders. These patients with somatic NRAS and KRAS mutations present with autoimmune phenomena, massive splenomegaly, modest lymphadenopathy and normal or only marginally elevated TCR alpha/beta+ DNT cells. Their lymph node histopathology is also not typical of ALPS-FAS. Additionally, these patients show abnormalities of the myeloid compartment, with chronic persistent monocytosis, mimicking juvenile myelomonocytic leukemia (JMML) in otherwise asymptomatic young patients. 3) Provided below is the current classification scheme that we have devised for ALPS patients based on the particular molecular defect present: ALPS-FAS : mutations in the TNFRSF6 (tumor necrosis factor receptor superfamily 6) gene, encodes the protein CD95 (Fas). ALPS-sFas: somatic mutant: TNFRSF6 gene defect in the double negative T (DNT) cell population. ALPS-FASLG: mutations in TNFSF6 gene, encodes the protein CD95 ligand (Fas ligand). ALPS-CASP10: mutations in CASP10 gene, encodes caspase-10. ALPS-U: associated mutation unidentified to date. 4) With support from NCBI we have implemented a web based publication of the existing databases of pathogenic FAS mutations, by far the commonest cause of ALPS, which is publicly available and can be used for diagnostic help by referring to NCBI NIH ALPS website <http://www.ncbi.nlm.nih.gov/lovd/home.php?select_db=FAS>. We are also continuing our efforts to streamline the techniques of apoptosis assay by evaluating Fas mediated cell death and cell survival with serum starvation in lymphocyte and monocyte subsets so that these test procedures can be readily adapted in more clinical laboratories for patient evaluation in ALPS and RALD respectively. 5) Characterized the pathophysiology and clinical phenotype of the second largest subgroup of ALPS patients in our cohort with somatic mutations in the FAS gene mostly limited to their ALPS signature cells, also known as double negative T lymphocytes. Confounding factors in the clinical presentation of ALPS and another hematological condition called HLH (Hemophagocytic lymphohistiocytosis) have been identified and clinicians are being advised to be aware of the distinguishing biomarkers in both conditions. We clarified and alerted readers about the pitfalls of misdiagnosing somatic ALPS patients as HLH in a publication (Pediatrics. 2013 Nov;132(5):e1440-4). 6) Extended the use of PET scans as an imaging modality in patients with ALPS associated lymphadenopathy as a tool to monitor patients with suspected ALPS associated cancer of the lymphoid system (lymphoma). We have identified lymphomas associated with ALPS-FAS in approximately 10% of our patients. Ongoing critical surveillance for lymphoma and its early diagnosis and treatment has been pursued over the last 20 years of longitudinal follow up of these patients. 7) Continued search for new genetic mutations in the subgroup of patients with ALPS and undetermined genetic defects using emerging genomic and cell biology tools. Currently a large group of patients with unknown molecular etiologies are being subjected to whole exome DNA sequencing and analysis. Some novel immunedysregulatory syndromes are identified and awaiting further work up, validation of candidate genes and publication during the coming years. 8) More recently the ALPS Clinical group has been repositioned as Clinical Genomics Unit of the Laboratory of Immunology to tackle new classes of immunological disorders with genetic underpinnings which has involved the recruitment of new members of the team as well as special inservices on genetics and molecular biology for the nursing and ancillary support staff.