Question

4. Describe the major techniques and approaches that are used for disease diagnosis (and prognosis, if applicable). ( Chronic granulomatous disease (Bridge -Good Syndrome).

• What are the main gene/molecular and cellular tests used to confirm diagnosis of your disease?

• How definitive are these tests? Do they work on their own? Do they rule in or out the gene as a cause of disease?

• How do these tests relate to the molecular genetics or immunopathology of the disease? Are they direct tests of the gene itself or surrogate measures of the gene’s effects?

Answer 1

Chronic granulomatous disease (CGD) is also referred to as Quie Syndrome. It is a hereditary immunodefiency characterised by dermatitis, hepatic and spleen enlargement, eczema and lung infiltration which is caused by mutation in CYBB and NCF 1 gene and impairment of nicotinamide adenine dinucleotide phosphate oxidase (NADPH). Pathogenic variants of the gene in this condition are CYBA, NCF1, NCF2, NCF4 and CYBB. Nitroblue tetrazolium test is one of the test used to measure the NADPH levels in the neutrophils. The blood sample is drawn from the peripheral blood vessels. The yellow colour NBT dye turns to dark blue colour due to the formation of formazan from reaction of NADPH which indicates its presence. Due to large variation in the result, this test is not in preference now a days. The gold standard of CGD diagnosis is flow cytometric dihydrorhodamine (DHR) in whcih phorbol myristate acetate is used to stimulate neutrophils and incubated with DHR which emits fluroscence with the help from the oxidation of hydrogen peroxide to produce rhodamine123. This test is useful to determine any X linked status including carrier of this condition.DHR flow cytometry helps to rule out the severity of the genetic abnormality. Genetic and prenatal testing could be carred out using amniocentesis if the pathogenic variants in the family is known.