Physical characteristics of young boys with fragile X syndrome: Reasons for difficulties in making a diagnosis in young males

Fragile X syndrome is the leading form of hereditary mental retardation, bu t the condition is still underdiagnosed in young children. Because of conce rn that the fragile X phenotype is subtle in young boys and therefore contr ibutes to underdiagnosis of the disorder, we evaluated 73 boys (36 with fra gile X and 37 same-age boys who were fragile X negative) using a checklist that we devised to learn which characteristics might be the most useful for alerting professionals to this diagnosis. After a multiple comparisons adj ustment, only 4 of 42 characteristics differed significantly in their distr ibutions between the two groups of boys (P < 0.0012), but 10 other items ma y also have predictive value for fragile X syndrome (P < 0.01). Four additi onal items occurred in at least 80% of boys with fragile X and may also be helpful for the clinician. Professionals who work with developmentally dela yed children should be aware of these 18 clinical characteristics and some of the behavior characteristics commonly seen in boys with fragile X so tha t they can readily diagnose patients. Am. J. Med. Genet. 92:229-236, 2000. (C) 2000 Wiley-Liss, Inc.