A simplified six-item checklist for screening for fragile X syndrome in the pediatric population

In our general experience, about 2% of samples referred for fragile X testing showed positive results on Southern blot analysis. The aim of this project was to determine whether screening criteria could be developed to increase the proportion of positive test results without sacrificing sensitivity.

We retrospectively analyzed nine clinical characteristics from patient records of 273 male and 62 female pediatric probands (average age, 5.7 years) referred for fragile X testing. The characteristics included mental retardation, family history of mental retardation, large or prominent ears, elongated face, attention deficit hyperactivity disorder, autistic-like behavior, simian crease, macroorchidism, and hyperextensible joints. These were scored as 2 if present, 1 If borderline present, and 0 if absent.

Analysis of the nine characteristics identified three (simian crease, macroorchidism, and hyperextensible joints) with low frequency and statistical insignificance, which were therefore eliminated. With the use of the remaining six characteristics, If a score of 5 or more was used as the criterion for requesting fragle X testing, then close to 60% of those tests from our patient population could have been eliminated without missing any positive cases. The validity of our threshold score of 5 was subsequently confirmed among an additional six cases of fragile X syndrome.

With our simplified six-item clinical checklist, 60% of testing could have been eliminated, thereby improving the cost-effectiveness of fragile X testing and increasing the proportion of cases with positive results by threefold.