Journal of Clinical & Experimental Pathology
Open Access

Abstract

Fragile X is the most common inherited cause of mental retardation with a prevalence of 1 in 4,000 for males and 1 in 5,000-8,000 for females. The American College of Medical Genetics and Genomics (ACMG) has recommended diagnostic testing for fragile X in symptomatic persons, women with ovarian dysfunction and persons with tremor/ataxia syndrome. Although medical and scientific professionals do not currently recommend screening non-symptomatic populations, improvements in current treatment approaches and ongoing clinical trials have generated growing interest in screening for fragile X. The choice of appropriate technologies and data interpretation depend on the relevant molecular basis of fragile X and fragile X testing. Current next-generation sequencing platforms and chromosomal microarray analysis commonly used for autism testing are not appropriate for detecting the large CGG repeats that are responsible for 99% of Fragile X. Southern blot analysis and commercial PCR reagents are commonly used in clinical settings for CGG repeat size and methylation estimation for these mutations, but do not meet the low cost needs of public health newborn screening programs. Our comparison of three different molecular technologies available for fragile X screening in both males and females include: Destabilizing the CGG-repeat region with betaine and using chimeric CGG-targeted PCR primers, using heat pulses to destabilize C-G bonds in the PCR extension step, and using melting curve analysis to differentiate expanded CGG repeats from normals. The first two-step method performed with high sensitivity and specificity. The second method provided agarose gel images that allow identification of males with expanded CGG repeats and females with expanded CGG-repeat bands which are sometimes faint. The third melting curve analysis method would require controls in each run to correct for shifting optimal cut-off values.

Biography

Email: pwm2@cdc.gov