Interphase behaviour of centromeric heterochromatin of chromosomes 1 and 16 has been investigated in lymphocytes and fibroblasts of patients with ICF syndrome and of normal subjects with non-isotopic in situ hybridization, using the satellite II-related probe pHuR 195. We found evidence for interphase somatic pairing in ICF lymphocytes with a frequency higher than that found in normal cells. Lymphocytes of ICF patients showed nuclear protrusions and micronuclei and these nuclear abnormalities consistently involved a hybridization signal. Somatic pairing was also present in fibroblasts, but with frequencies similar in normal and ICF subjects. The fibroblasts do not have the major chromosomal abnormalities found in lymphocytes. The degree of heterochromatin condensation in fibroblasts was lower than that in lymphocytes and we postulate that the more decondensed state of chromocentres in the fibroblasts could be the reason for the absence of the major chromosomal abnormalities.

Cytogenetic studies on an azoospermic male revealed a balanced Y;l translocation: 46, X, t(Y;l)(ql2;p34.3). In situ hybridization with the probe St35–239 (DXY64) and with a probe detecting telomeric sequences revealed that only the Y telomere is involved in the translocation. Fluorescence in situ hybridization with a chromosome 1 library on meiotic preparations revealed consistent contact of the painted chromosome 1 with the sex vesicle at pachytene, the most advanced stage of spermatogenesis observed. No deletions were observed after Southern blot analysis with probes p49f (DYS1), 50f2 (DYS7), and 52d (DYF27), which map in interval 6 of the Y chromosome, which includes the azoospermia factor (AZF) gene. The results indicate that the infertility of the translocation carrier could be due to an alteration of the sex vesicle structure or to a disturbance of X-chromosome inactivation as a result of the proximity to the autosomal portion.

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