Cytogenetically negative, linkage positive "fragile X" syndrome.
We investigated the family of a 3-year-old boy with manifestations of the Martin-Bell syndrome (MBS). His 17-year-old cousin had classic manifestations of MBS and was fragile X [fra(X)] positive. The 3-year-old boy was fra(X) negative. Linkage analysis with probes flanking the fra(X) region indicated that these cousins had the same X chromosome inherited from a normal grandfather. The DNA and cytogenetic analyses suggest that limitations in the ability to detect the fra(X) mutation cytogenetically may be responsible for fra(X)-negative MBS; or, alternatively, that a crossover occurred between a locus determining the MBS phenotype and one determining fra(X) expression.
Sklower Brooks
S
S
Department of Human Genetics, New York State Office of Mental Retardation and Developmental Disability, Staten Island 10314.
Cohen
I
I
Ferrando
C
C
Jenkins
E C
EC
Brown
W T
WT
Dobkin
C
C
D000293:Adolescent; D002675:Child, Preschool; D015342:DNA Probes; D005188:False Negative Reactions; D005260:Female; D005600:Fragile X Syndrome / Q000235:genetics*; D005819:Genetic Markers; D006801:Humans; D008607:Intellectual Disability / Q000235:genetics; D007621:Karyotyping; D008297:Male; D010375:Pedigree; D012150:Polymorphism, Restriction Fragment Length; D011995:Recombination, Genetic
D015342:DNA Probes; D005819:Genetic Markers