TWO SIBLINGS WITH FRAGILE X SYNDROME
Abstract
Th.e fragile X syndrome is the most common spe- cific cause of familial mental retardation. It is asso- ciated with fragility at Xq27.3. Because of varia- tions in route of inheritance and clinical features, ° it can only be diagnosed through genetic studies. However, cytogenetic éxfi›ression levels of fragility in lymphocytes show variation, and r is not always possible to identify affected males with a /ower degree of fragility expression using cytoge- netic techniques.
In this study, two siblings with Martin-Bell phe- notyfiie are reported. A/though they had typical clinical findings and positive family history, fragili- ty at Xq27.3 could not be demonstrated in the first cytogenetic studies. Two years later, in re|oeated cultures of the siblings, 2%- and 5%-fragility was found. The conflicting results of repeated cultures confirmed that the expression variability of fragili- ty might be the reason for false negative cytoge- netic results in affected patients with low fragility ratios.
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References
- 1. Wohrle D, Fryns JP, Steinbach P. Fragile X expression and X inactivation. Hum Genet, 1990; 85:659-65. 2. Fryns JP. X-linked mental retardation and the fragile X syndrome: a clinical approach. In: Davies KE, ed. The Fragile X Syndrome. Oxford: Oxford University Press, 1989:1-29.
- 3. Hagerman RJ, Amiri K, Cronister A. Fragile X checklist. Am J Med Genet, 1991; 38:287-97.
- 4. Sutherland GR. The detection of fragile sites on human chromosomes. In Adolph KW, ed. Advanced techniques in chromosome research. New York: Marcel Dekker, Inc., 1991:203-22.
- 5. Tommerup N. Cytogenetics of the fragile site at Xq27. In: Davies KE, ed. The Fragile X Syndrome. Oxford: Oxford University Press, 1989:103-35.
- 6. Yalaz K, Epir §. Physical growth measurements of preschool urban Turkish Children. Turk J Pediatr, 1983; 25:155-65.
- 7, Watt JL, Stephen GS. Lymphocyte culture for chroanalysis. In: Rooney DE, Czepulkowski BH, eds. Human Cytogenetics a Practical Approach. Oxford: IRL Press, 1986:39-56.
- 8. Sutherland GR, Ashforth PLC. X-linked mental retardation with macroorchidism and the fragile site at Xq27 or 28. Hum Genet 1979; 48:117-20.
- 9. Chudley AE, Knoll J, Gerrard JW, et al. Fragile (X) Xlinked mental retardation |: relationship between age and intelligence and the frequen y of expression of fragile-(X) (q28). Am J Med Genet, 1983; 14:699-712.
- 10. Cantu E, Jacobs PA. Fragile (X) expression: relationship to the cell cycle. Hum Genet, 1984; 67:99-102.
- 11. De Arce MA, Hecht F, Sutherland GR, Webb GC. Guidelines for the diagnosis of fragile X. Clin Genet, 1986; 29:95.