[A cytogenetic study of the functions of the variable regions in human C heterochromatin. I. The effect of C heterochromatin on gene expression].

In our previous studies we have demonstrated that the degree of the growth retardation shows a positive correlation with the reduction of C heterochromatin in chromosomes 1, 9, and 16 in patients with embryopathies of unknown etiology and in children with trisomy 21. The investigation of C heterochromatin in these chromosomes in patients with obligate growth retardation and gene syndromes with a postulated Mendelian inheritance (Russell-Silver, Dubowitz etc.) has revealed a reduced C heterochromatin amount. No large C segments were seen in all of the 32 patients. Only 2 large C segments were found in 42 parents that were never inherited. The lowest amount of C heterochromatin was found in the most shortish fathers and mothers. The short stature of healthy parents in patients with the above mentioned syndromes is usually regarded as resulting from an incomplete mutant gene expression. The present results, when taken in conjunction with those of our previous study, enable us to suggest another interpretation: (i) the growth retardation in children with gene syndromes and low height of parents may be due to the reduction of C heterochromatin in chromosomes 1, 9, and 16, i.e. the mutant genes are not the only reason of the growth retardation; (ii) the obligatory growth retardation in the above syndromes can be explained by the fact that the expression of corresponding genes is possible only in genomes with a low C heterochromatin amount; (iii) the C heterochromatin in chromosomes 1, 9, and 16 influences on the number of mutant genes expression in man.(ABSTRACT TRUNCATED AT 250 WORDS)