The marker (X) syndrome: a cytogenetic and genetic analysis

• DOI: 10.1111/j.1469-1809.1984.tb00830.x
• Publication Date: 2007-09-28T09:50:08Z
• Authors: S. L. Sherman; N. E. Morton; P. A. Jacobs; G. Turner
• Keywords: Penetrance; Pedigree chart

Summary The results of a cytogenetic and segregation analysis 110 pedigrees the mar (X) syndrome are reported. study indicated an inverse relationship between IQ mar(X) frequency in females but not males. A small significant effect age on was observed both males females, it restricted to those normal intelligence, retarded showing no effect. Classical performed using program segran , analyzing sexes separately. 20% deficit affected observed, most plausible explanation for majority these cases being incomplete penetrance. since this unexpected result, data were scrutinized possible biases; however, correction had little estimate. penetrance mental impairment carrier estimated be 30% and/or mar(x) expression 56%. thus 44% carriers cannot detected with our definition affection. evidence sporadic among found. complex sex‐linked version pointer analysing together. done order test from classical analysis, family resemblance estimate mutation rates. confirmed that there males, that, approximately evidence: sporadic: all gene appear t o have received their mothers mutations must occur sperm. rate sperm as high 7·2 × 10 ‐4 implying over one‐half random fresh mutants. important implications genetic counseling they imply isolated carriers, brothers 17% chance carrying transmitting daughters, sisters have, at most, carriers. biases due testing particular individuals, probabilities considered approximations until independently confirmed.