Patched homolog 1 (PTCHI) gene mutations can predict the outcome of chronic myeloid leukemia patients?

Background: The Hedgehog (Hh) pathway is stimulated by inactivating mutations of Patched Homolog 1 . There is accumulating evidence that Hh signaling plays a critical role in the pathogenesis of various haemopoietic malignancies. Particular interest has focused on the role of Hh signaling in chronic myeloid leukemia (CML). The Hh signaling is increased in BCR-ABL+ve progenitor cells and Hh signaling is further up regulated with disease progression.

Aim: The aim of this study was to determine the frequency and types of PTCH1 gene mutations in Chronic Myeloid Leukemia (CML) patients and to correlate the effect of these mutations on the prognosis and outcome of CML and for predicting the imatinib response in CML patients.

Subjects And Methods: The study included fifty newly diagnosed CML patients and ten healthy volunteers (the control group) to verify the presence or absence of PTCH1 gene mutation. The patients were subjected to clinical examination, routine laboratory investigations, bone marrow examination, Cytogenetic evaluations of t(9;22) and molecular study of BCR-ABL fusion gene. All participants in this study were subjected to the assessment for the presence of PTCH1 gene mutation by DNA extraction followed by polymerase chain reaction (PCR) of genomic DNA corresponding to exon 23 of PTCH1 gene, purification of amplified PCR product, followed by sequencing analysis for detection of PTCH1 gene exon 23 mutations and the types of these mutations.

Results: Four types of mutations of PTCH1 gene were detected in 24 CML patients (48%), three types of them were missence while the fourth type was frame shift mutation. There was no significant association between PTCH1 gene mutation and percent of BCR-ABL fusion genes at level less than 10% at 3 months of treatment, complete cytogenetic response (CCyR) at one year, disease free survival and overall survival. However there was significant association between PTCH1 gene mutation and imatinib failure (P=0.03).

Conclusion: PTCH1 gene mutation should be considered a promising molecular marker for predicting the probability of imatinib response in CML patients. Hedgehog pathway activation in CML patients can raise a possibility that combinations of ABL and Hh inhibitors might offer a new treatment strategy in CML and might help to effectively cure this disease.