Impact Of Fish Analysis In Different Research Areas

Studies on Normal Men

More than 5 million sperm cells from more than 500 normal men have been analyzed by a number of laboratories from around the world.[7] These studies have included the frequency and distribution of aneuploidy in sperm cells, and the effect of donor age, lifestyle factors, and geographical and ethnic factors.

Frequency and Distribution of Aneuploidy

The frequency and distribution of disomy in human sperm cells is of interest to determine the normal baseline values and to determine if all chromosomes have a similar frequency of nondisjunction or if some are particularly predisposed to nondisjunction.1-8-1 The frequencies of disomic sperm for an individual chromosome are considerably different among the studies. For example, for chromosome 21, the lowest disomy frequency was 0.05%[9] and the highest was 0.95%.[10] It is unlikely that these differences arise only from interindividual variation in disomy. Rather, different approaches in the experimental design, different probes, and scoring criteria used are regarded as being responsible (for a review, see Ref. [11]). This makes it essential for each study to have controls analyzed in the same laboratory.

In a composite analysis of the distribution of disomy frequencies in studies on normal men, the mean disomy frequency for autosomes was 0.15% and 0.26% for sex chromosomes.[7] Our laboratory has determined that most autosomes have a similar frequency of nondisjunction, but chromosome 21 and the sex chromosomes have a significantly increased frequency.[8,12] These results corroborate our earlier studies in human sperm karyo-types.[13] This has also been confirmed by other groups.[14,15] Thus we see aneuploidy for all chromosomes, but chromosome 21 and the sex chromosomes appear to be particularly susceptible to nondisjunction during spermatogenesis.

Effect of Donor Age

There have been a number of FISH studies addressing the possibility of a paternal age effect on nondisjunction. The great majority of studies has not found a paternal age effect for autosomes.[16-18] However, most studies have demonstrated a significant increase in the frequency of sex chromosomal aneuploidy with donor age[19-21] with approximately a doubling of disomy frequencies in the oldest donors compared to the youngest donors.

Lifestyle Factors

A small number of studies have addressed the possible effects of lifestyle factors such as smoking, air pollution, and caffeine and alcohol consumption on sperm aneuploidy frequencies. Robbins et al.[22] found a significant association between caffeine and alcohol consumption and increased disomy frequencies for some chromosomes. No significant association was noted for smoking. Two studies found a significant association between smoking and aneuploidy for some chromo-somes,[23,24] but it is difficult to rule out combined lifestyle factors because smokers also consume more caffeine and alcohol than nonsmokers. Our laboratory studied over 600,000 sperm cells from heavy smokers, light smokers, and nonsmokers (all nondrinkers of alcohol) and found a significant increase of disomy only for chromosome 13, but not for chromosome 21, X, or Y.[25,26] Perreault et al.[26] studied seasonal air pollution and found an association between high levels of air pollution and YY disomy in nonsmoking men. To date, no consistent and clear association has been discovered between disomy frequency and any type of lifestyle factor. More well-controlled studies will be required to uncover any associations.

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