NeuroPsychological Traits-Diversity: X-inactivation Mosaicisms

Teresa Binstock binstoct at ESSEX.HSC.COLORADO.EDU
Fri Jun 23 04:42:13 EST 1995


>>>On Thu, 22 Jun 1995, Richard Gordon wrote:
> The calico-cat effect should also lead to left/right hemispheric 
> asymmetries exceeding those normally found.
> -Dick Gordon, U.Manitoba[Jun22,95]

TERESA REPLIES:

1. The X-inactivation mosaicism would induce pleiotropic diversity of 
neuropsychological traits only in cases of (i) mutated X-chromosome genes 
affecting neuronal development and/or function (eg genes for MAO-A or for 
FMR-1 re: fragile X syndrome, etc).

2. This kind of mosaicism occurs only in females, who have in each cell a 
maternal-X and a paternal-X, only one of which is active in any given 
cell (Lyonizatin hypothesis by Mary Lyon, 1961, and still supported by 
data from numerous studies and not disproven).

3. The study by Happle (Arch Dermatol) cited in my original posting 
shows an example of total left/right mosaicism, which Happle calls 
infrequent. 

a. This "rare" left/right mosaicisim might induce opposite 
asymmetry effects in different individuals depending upon what side (L or 
R) had the mutated gene as active. 

b. Even in some cases of monozygotic twin females, one twin might have a 
left sided activation of the mutation and the other twin might have a right 
sided activation of the mutation. 

4. Far more frequently, the "calico-cat" effect would not be arranged in 
left/right separation. According to visually observable patterns of 
X-linked mosaicisms of human skin (eg as illustrated in the Rudolf Happle 
study), various "calico cat" patterns are possible. According to the Tan 
et al study (Development 121.1029-39 1995) the in-brain mosaicisms are 
three dimensional and complexly "calico-esque". 

5. Consider the case of 200 females tested for left/right hemispheric 
effects and consider that of the 200, one hundred have normal 
X-chromosomes and one hundred have mutations of the same X-chromosome 
gene affecting cognition, emotion, and behavior (ie aspects of CNS 
function). 

a. The data from normal X-chromosomes females would show fairly 
traditional curves re left/right hemispheric effects.

b. The data from females with either a maternally or paternally inherited 
X-chromosome mutation of a gene affecting CNS function would be more 
diversely and complexly patterned. 

6. I can't help but think that some such mutated X-gene individuals would 
show increased left-like tendencies, some just the opposite, and most 
subjects would present blurrings of traditional left/right distinctions 
for any given trait.

		***       ***       ***       ***       ***

How X-linked mosaicisims would affect left/right asymmetry and related 
scores on cognitive and/or emotional measures is quite challenging. 
You've raised a good point. Further input re: "mosaicisms meet L/R 
asymmetries" will be important to understanding both the mosaicisms and 
the asymmetricalities...

Thank you for the reply...

Teresa B



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