[Fragile X chromosome and X-linked mental retardation (author's transl)].
In males affected by a special form of X-linked mental retardation a characteristic chromosomal abnormality can be demonstrated, - i.e. a fragile site on the long arm of the X chromosome, fra(X) (q27 or 28) (marker-X chromosome). Male carriers are physically normal, but in most cases show macroorchidism. The demonstration of the marker-X chromosome requires special cell culture conditions, above all a folic acid-deficient medium. The frequency of cells with fragile X chromosome varies interindividually, ranging from 2 to 50%. In female heterozygous carriers the number of cells with fra(X) decreases with age and cannot be demonstrated in some cases. Distribution and frequency of X-linked mental retardation with marker-X chromosome and macro-orchidism are discussed, as well as possibilities of prenatal diagnosis of this disorder.
D000293:Adolescent; D002871:Chromosome Banding; D005260:Female; D005808:Genes, Recessive; D006059:Gonadal Dysgenesis / Q000150:complications; D006579:Heterozygote; D006801:Humans; D008607:Intellectual Disability / Q000150:complications / Q000175:diagnosis / Q000235:genetics*; D008297:Male; D011247:Pregnancy; D011296:Prenatal Diagnosis; D012730:Sex Chromosomes; D013737:Testis / Q000002:abnormalities; D014960:X Chromosome
Fragiles X-Chromosom bei X-chromosomal rezessiv vererbtem Schwachsinn.