Fragile X expression increased by low cell-culture density

Microcephaly, muscular build, rhizomelia, and cataracts: description of a possible recessive syndrome and some comments on the use of electronic databases in syndromology

We report on a 7-year-old boy born of consanguineous parents with severe microcephaly (-5 SD) but borderline intelligence, juvenile cataract, muscular build, rhizomelic shortness of limbs predominantly of femora, advanced bone age, and micropenis. This combination of signs appears unique and may represent an undescribed, possibly autosomal recessive MCA syndrome. The use of LDDB and POSSUM in the workup of such "new syndromes" is reviewed. Three search strategies are discussed: single rare sign browsing, best combinatory fit using an array of key words, and combined rare signs scan. Pitfalls in the use of such databases and the some problems raised by inconsistent/ incomplete encoding in those two popular, highly useful syndromology retrieval systems are discussed.

Transmission electron microscopy of chromosomes by longitudinal section preparation: application to fragile X chromosome analysis

We developed a method for the preparation of ultrathin longitudinal sections of chromosomes enabling TEM studies of whole chromosomes. By using a novel "repeat chill" method of exposing the glass slide and plastic block interface to liquid nitrogen, it was possible to separate consistently hardened epoxy resin-embedded chromosome spreads from glass slides for ultrathin longitudinal sectioning of entire spreads and of individual chromosomes. The method was applied to analyze the fragile X chromosome. The ultrastructure of centromeres, telomeres, fragile sites and other chromosomal areas can now be studied in detail.

Tissue-specific methylation differences and cognitive function in fragile X premutation females

Tissue-specific variation in (CGG)n repeat size and methylation status of the FMR1 gene was investigated in 17 female premutation carriers. Minor variation in premutation repeat size among leukocyte, lymphoblast, and fibroblast tissues was noted in some subjects. One subject exhibited a premutation size allele of (CGG)64 in leukocyte and fibroblast tissues by polymerase chain reaction analysis but a normal-size allele of (CGG)46 in lymphoblast cells, suggesting low-level mosaicism in blood and clonality of the lymphoblast cell line. Six subjects exhibited differences in methylation pattern between leukocytes and lymphoblasts but not between leukocytes and fibroblasts, whereas 2 subjects showed large differences in methylation pattern between leukocytes and fibroblasts. Cognitive function was studied in 14 subjects using the Wechsler Adult Intelligence Scale-Revised. Mean Verbal and Performance IQs were well within the average range as was the mean Full Scale IQ; nevertheless, a trend toward lower Performance IQ compared with Verbal IQ was observed. No significant correlation was apparent between Full Scale IQ and (CGG)n repeat size; however, a significant positive correlation was observed between Full Scale IQ and the proportion of the active X carrying the normal FMR1 allele in fibroblasts but not in leukocytes or lymphoblasts.

Effects of hyperoxia and caffeine on the expression of fragile site at Xq27.3

To enhance the cytogenetic expression of the fragile X chromosome, we studied the effects of hyperoxia and caffeine on the induction of fragile Xq27.3. A lymphoblastoid cell line (GM 06912) derived from a fragile X male proband was cultured in RPMI 1640 containing 16% dialyzed fetal calf serum. The cells were synchronously subjected to one of 3 different atmospheric oxygen tensions (21%, 21.3 kPa, normoxic; 40%, 40.5 kPa, hyperoxic; or 60%, 60.8 kPa, hyperoxic) during the last 24 hours of the 72 hour culture, immediately after the addition of 2'-deoxy-5-fluorouridine (FUdR) at 25 ng/ml. To study the enhancing effect of caffeine, with or without hyperoxia, a second set of cultures was additionally subjected to caffeine (2.5 mM) during the last 6 hours of the culture. When the fragility of hyperoxic cells (38.1 kPa dissolved oxygen) was compared to that of normoxic control cells (13.3 kPa dissolved oxygen), the difference was significant (P < 0.05). These data suggest that there is a mean increase in the fragile Xq27.3 expressivity as the dissolved oxygen tension increases. Additionally, we observed that caffeine, with or without hyperoxia, significantly (P < 0.05) suppressed the expression of the fragile X site in this lymphoblastoid cell line.

Effect of aluminum chloride on mitogenesis, mitosis, and cell cycle in human short-term whole blood cultures: lower concentrations enhance mitosis

Aluminum, the third most common element in the earth's crust (second to oxygen and silicon) and recently suspected by some investigators to be implicated in Alzheimer disease etiology, has been studied in relation to its effect on mitogenesis, mitosis, and cell cycle. We have observed that 2-4 mM concentrations of AlCl3 have decreased the number of cells that undergo mitogenesis (PHA-induced blast transformation) and mitosis in human short term whole blood cultures. We have also shown that the rate of the cell cycle was slowed down, i.e., cell cycle time was increased in the presence of AlCl3. Also, we have demonstrated a reversible effect on aluminum-induced reduced mitotic index in long-term EBV-transformed lymphoblastoid cultures. Although safeguards such as limiting aluminum serum concentrations have been recommended to protect individuals undergoing dialysis, it should be realized that concentration accumulations of aluminum may increase over chronic exposures. Accordingly, if the number of cells stimulated by PHA is reduced in the presence of AlCl3, there may be a reduction of immune competence, since the degree of PHA stimulation has been used as an indicator of immune response. Similar reductions in mitotic index could affect every tissue involved with cell division. Although it may not be the same for higher concentrations, from our results, we have also shown that decreased mitotic rates were reversible in long-term EBV-transformed lymphoblastoid cultures. Increased numbers of mitoses were observed in human short-term whole blood cultures that were exposed to 2 microM concentrations of aluminum chloride.(ABSTRACT TRUNCATED AT 250 WORDS)

Genetic and other factors that contribute to variability in cytogenetic expression in fragile X males

Variability in cytogenetic expression of fragile X has been observed by many investigators. One recent study of families of fragile X brothers concluded that frequency of expression was almost completely controlled by genetic factors. We investigated the extent of genetic control over frequency of expression by evaluating fragile X families from 3 different sources using hierarchal analysis of variance model to calculate the intraclass correlation and the index of heritability, h2. Proportion of variance attributable to families was computed from 2 estimation procedures: 1) a least squares method and 2) a maximum likelihood technique. Results were comparable with one another and indicated that, although genetic factors were significant, differences between laboratories contributed a larger proportion of the total estimated variance. These results partly confirmed previous findings but indicated that the degree of genetic control over the proportion of affected cells was lower than recently suggested.

Fragile X expression in short-term whole blood cultures is affected by cell density

The effect of cell density on expression of the fragile site at (X)(q27.3) in short-term whole-blood cultures from patients with fragile X [fra(X)] or Martin-Bell syndrome was studied. A significant increase in fra(X) frequency was observed in 7 of 8 samples when cell density was decreased. Higher fra(X) frequency was not always noted at below-routine density, but in some cases fra(X) expression was depressed at above-routine density. We conclude that decay of the FUdR effect explains the fact that fra(X) expression is affected by culture density. It is significant that a relationship exists between the two; it suggests that in order to maximize fra(X) expression in cases with low-percentage fra(X) with standard methods, cell density may have to be adjusted. It is possible that in individuals who are normally nonexpressing, such as some obligate female carriers and nonpenetrant males, fra(X) expression may be sensitive to cell density effects.