Pramod Kumar Mistry MBBS, PhD, F.R.C.P.
Professor of Pediatrics (Gastroenterology) and of Medicine (Digestive Diseases); Chief, Pediatric Gastroenterology & Hepatology; Director, National Gaucher Disease Treatment Center
Gaucher's disease: Molecular genetics, Genotype/phenotype correlations modifier genes, Animal models and therapies; Wilson's disease; Glycogen storage disease type 1a
- GBA1 gene analysis and genotype/phenotype correlations
- Identification of novel Gaucher phenotypes
- Search for modifier genes of Gaucher's disease via candidate gene and GWAS approaches.
- Mouse models of Gaucher disease
- Therapy of Gaucher disease with enzyme replacement, substrate depletion and small molecule pharmacological chaperones.
- Genotype/phenotype studies in Wilson's disease
- Hepatic adenomas/HCC in glycogen storage disease type 1a.
The major focus of my research is Gaucher disease. The key areas that are under active investigations are:
- Development of clinical tools to define the spectrum, severity and sub-types of Gaucher disease;
- Genetic mutations causing Gaucher disease in defined populations, i.e., Egypt and India;
- Correlation of genetic defects with disease severity and manifestations;
- Development of serum biomarkers of Gaucher disease activity to aid patient monitoring and understand disease mechanisms;
- We are participating in several clinical trials of recombinant enzyme replacement therapies and small molecule therapies for Gaucher disease;
- Recently, we developed an authentic mouse model of type 1 Gaucher disease that replicates human disease entirely. This is a key development to enable mechanistic understanding of Gaucher disease and develop novel treatments;
- We are conducting genome-wide association study to understand the role of modifier genes in the hope that we may be able to predict future disease severity accurately and plan pre-emptive therapy for vulnerable patients.
Extensive Research Description
My lab and program has a major focus on Gaucher disease on several topics including analysis of gene encoding lysosomal glucocere brosidase (GBA1), genotype/phenotype correlations, modifiers of Gaucher's phenotype, identification of novel Gaucher phenotypes through careful annotation of diverse phenotypes, macrophage-targeted enzymere placement therapy and development of murine models of the disease. We have used Gaucher's disease as a prototype single gene disorder affecting the liver to address other inherited metabolic liver diseases including Wilson's disease and glycogen storage disease type 1a.
My lab has developed methods to analyze complex GBA1 gene locus that harbors highly homologous pseudogene containing numerous known disease mutations; gene conversion events may to lead to transfer of pseudogene mutation to the active gene. Methods of gene analysis include ARMS-PCR and meta-PCR that permits resolution of active gene and pseudogene sequences. We are characterizing large populations of patients homozygous for N370S mutation (only found in active gene sequence and the most common disease mutation in people of Ashkenazi Jewish ancestry) and L444P mutation (the mutation present in normal pseudogene sequence and the most common pan-ethnic mutation world-wide). L444P homozygous genotype leads to severe disease with neurological involvement while N370S homozygosity leads tonon-neuronopathic Gaucher disease of extraordinarily diverse pattern. We recently showed that N370S homozygous Gaucher leads to adult onset disease with mild visceral involvement but progressive skeletal disease and high risk of multiple myeloma and other hematological malignancies. Similarly in characterizing a large cohort of Egyptian patients, we found L444P homozygous mutation leads to childhood onset of severe visceral and pulmonary disease with variable severity of neurologic disease.
We are examining several candidate genes in glycosphingolipid metabolic pathways and in pro-inflammatory pathways as potential modifier genes. We are also applying several genomic approaches to identification of modifier genes. Discovery of modifier genes will impact on patient management through more accurate prediction of prognosis and pre-emptive therapy of those at highest risk.
We have had a long-standing interest in macrophage-targeted enzyme replacement therapy with recombinant glucocere brosidase expressed in CHO cells (imiglucerase), its efficacy in reversing multiple aspects of Gaucher's disease and its mechanism of action. We are an approved center for treatment IND issued by the FDA for mannose-terminated glucocere brosidase produced in human fibroblast cell line via gene activation technology (velaglucerase). We are also an approved site for an international multicenter phase 3 trials of a small molecule ceramideanalog Genz 112368, that is an inhibitor of glucosylceramide synthase, exploiting substrate depletion approach to treatment of Gaucher disease. An important goal for us in the therapeutic area is small molecule pharmacological chaperones. To facilitate these studies, we are currently developing viable murine models harboring classic protein folding trafficking mutations of GBA1, i.e., N370Sand G202R.
Despite the extraordinary success of enzyme replacement therapy in Gaucher disease, virtually nothing is known about the true mechanism of action beyond proposed depletion of glycolpid-filled Gaucher's macrophages. We are currently conducting studies to address organ, cellular and gene expression responses to enzyme replacement therapy in our murine models.
A major limitation for further delineation of Gaucher disease has been lack of viable models of the disease that mimic human disease due to embryonic lethality. We have used CreLox technology to conditionally KO GBA1 in hematopoietic organs. This approach has led to an authentic mouse model of type 1 Gaucher disease, that recapitulates the entire human phenotype. Already this model is providing exciting new insights into disease mechanisms including important role of the adaptive immune system in development of the disease.
Investigation of Gauche disease is an excellent paradigm for delineation of other inherited metabolic diseases affecting the liver. In particular we are interested in Wilson’s disease and glycogen storage disease type 1a. Wilson's disease is also characterized by extreme phenotypic diversity and multiplicity of ATP7Bmutations with very poor genotype/phenotype correlations. We are exploring the possibility of genetic heterogeneity and are currently assembling appropriate pedigrees to conduct genome-wide association studies.
Much metabolic diseases increase cancer risk, as we delineated for Gaucher disease. In glycogen storage disease type 1a, the incidence of hepatic adenomas is increased and there is high risk of transformation to hepatocellular carcinoma, despite good metabolic control. We are conducting gene expression and genomic studies on tissues obtained at liver transplant inGSD1a. In the longer term we want to develop a long-lived mouse of GSD1a to study how and why adenoma develops in GSD1a and the steps that lead to hepatocellular carcinoma.