Abstract
The effect of the fragile X allele on ridge breadth, height and testicular volume was examined using robust statistical techniques for the data collected from 8 families from Ibadan, south west Nigeria, afflicted with this disorder. There is the presence of outliers, an estimated 6.5% for testicular volume and 1.3% for ridge breadth and height data respectively. It is shown that fragile X affects ridge breadth, height and testicular volume in a different manner. Fragile X women had a greater mean ridge breadth than normal women; a pattern similar to normal and fragile X men but the differences were not significant. Fragile X men were shorter than normal men, but no significant difference between the mean height of normal and fragile X women was observed. Whereas fragile X girls were shown to grow more quickly and to stop growth earlier than normal girls, normal women were taller than fragile X women. Testicular volume in fragile X boys continue in development long after normal boys have stopped; an observation that could explain the significant difference in means of adult males. An examination of the covariance between relatives classified according to fragile X status showed that for the three traits the influence of fragile X alleles was to reduce the covariance between parents and offspring, the effect of which produces a departure from an additive polygenic model of inheritance. Key words: Fragile X allele, ridge breadth, testicular volume, single-gene disorder.
Highlights
Of one of the most frequent single-gene disorders recognised in humans, the fragile X is of particular interest and concern because it is one of the most frequent and it represents a wide spectrum of clinical manifestations including intellectual capability and physical defects (Garber et al, 2008; Kabakus et al., 2006)
The robust estimates of parameters for testicular volume in fragile X males and their normal male relatives presented in Table 7 show that testicular volume mean is Categories according to age, sex and fragile X status
The effect of fragile X on the mean values of one dermatoglyphic, and two anthropometric measurements was demonstrated, where this effect is estimated against the background of the normal hereditary variations of these quantitative traits
Summary
Of one of the most frequent single-gene disorders recognised in humans, the fragile X is of particular interest and concern because it is one of the most frequent and it represents a wide spectrum of clinical manifestations including intellectual capability and physical defects (Garber et al, 2008; Kabakus et al., 2006). The molecular basis of fragile X has the form of an unstable CGG repeat within the “fragile X mental retardation” (FMR1) gene (Glover-Lopez and GuillenNavarro, 2006; Verkerk et al, 1991). The expansion of this repeat beyond a particular threshold causes transcriptional suppression. The instability of the CGG repeat combined with other features of the fragile X genotype (Terracciano et al, 2005; Heitz, et al, 1992; Warren and Nelson, 1994) complicates the genotypephenotype relationship in this condition.
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