How is the diagnosis of A-T made?
A simple alphafetoprotein (AFP) blood test. The AFP is elevated in the blood in >95% of patients. Karyotyping usually reveals characteristic translocations between chromosomes 7 and 14. An MRI will show (after 7 or 8 years of age) that the cerebellum is shrinking in size. The absence of ATM protein and its various functions can be documentated in the laboratory by a blood test. The sensitivity of A-T cells to ionizing radiation is also markedly increased. In a experienced laboratory, DNA sequencing can confirm the presence of mutations in both copies of the very large ATM gene. DNA sequencing can also be used to identifiy carriers; however, this is expensive because of the size of the gene. A more rapid method of carrier detection is being developed.
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