Hum Genet (1985) 70 : 8%91 © Springer-Verlag 1985 Clinical case report Deletion of band 13q21 is compatible with normal phenotype J. Couturier 1 , N. Morichon-Deivallez 2, and B. Dutrillaux 1 1C.N.R.S., U.A. 620, Structure et Mutagen6se Chromosomiques, Institut Curie, Section de Biologie, 26 rue d'Ulm, F-75231 Paris Cedex 05, France 2Laboratoire de Cytog6n6tique, Centre Hospitalier R6gional et Universitaire, place Victor-Pauchet, F-80000 Amiens, France Summary. A deletion of band 13@1, of maternal origin, was found in a male whose wife had had two miscarriages. The proband and his mother were both phenotypically normal. Repeated studies by high resolution banding techniques failed to demonstrate a translocation of the deleted band in the two subjects. The absence of pathological consequences of the deletion is explained by the fact that this band is one of the latest replicating in the human karyotype, which may indicate, by analogy with heterochromatin, that it carries no transcrip- tionally active genetic material. Introduction As a general rule, imbalanced autosome abnormalities cause their carrier to have an abnormal phenotype and/or mental deficiency. Nevertheless, it was noticed (Aurias et al. 1978; Korenberg et al. 1978) that this rule should be modified ac- cording to the nature of the chromosome segment lacking or in excess: imbalances involving R-bands have greater pheno- typical consequences than those involving G-bands. We de- scribe here the first case, studied by high resolution banding techniques, of an autosomal deletion associated with a normal phenotype; the deletion concerns a G-band of large size, i3q21, which is very late replicating. attempt to demonstrate a hidden translocation. It is difficult to obtain a complete picture of the high resolution karyotype of a subject from only two figures (Figs. 1 and 2), but 25 good quality karyotypes were set up and we failed to detect any translocation of this band, although it is of an appreciable size. Thus, it can be concluded that this subject is a carrier of a nearly complete deletion of 13q21; only a very small part of this band, for which it is not possible to know whether it is q21.01 or q21.09, remains on the deleted chromosome. The study of the family (Fig. 3) led to the finding of the same deletion in the mother of the proband, who also had a normal phenotype and no history of miscarriages. She was not seen at the laboratory but, according to her doctor, her intel- lectual level was normal; now retired, she had had a normal professional career. Again, no translocation could be detected by high resolution banding. The maternal grandmother had a normal karyotype and the grandfather was dead. No abnor- mal karyotypes were found among the sibs. Shortly after the cytogenetic examination, the wife of the proband became pregnant and the question of the need for amniocentesis was raised by gynaecologists. As it would be impossible to draw any conclusion in the case of the discovery of the deletion in the karyotype of the foetus, it was decided not to carry out a prenatal diagnosis. Finally, the mother gave birth to a normal boy, the karyotype of which comprised two normal chromosomes 13. Clinical observations and cytogenetic studies The proband was a man aged 25 years, phenotypically and mentally normal, without a remarkable medical history, examined because his wife had had two miscarriages. His IQ has not been tested but he attended secondary school and now has a position of middle executive in postal administration. Routine cytogenetic analysis, normal in his wife, showed an apparently unbalanced karyotype with an intercalary deletion of chromosome 13, in band q21. Two further examinations using R- and G- high resolution banding techniques (Vie- gas-P6quignot and Dutrillaux 1978; Dutrillaux and Viegas- P6quignot 1981) were carried out to locate the deletion and to Offprint requests to: J. Couturier, C.N.R.S., U.A. 620, Structure et Mutagen6se Chromosomiques, Institut Curie, Section de Biologie, 26 rue d'Ulm, F-75231 Paris Cedex 05, France Discussion Interstitial deletions of 13q and microdeletions responsible for retinoblastoma (Yunis and Ramsay 1978; Turleau et al. 1983) are now well documented (for reviews see Noel et al. 1976; Niebuhr 1977; Nielsen et al. 1977; Cuschieri et al. 1977; Nichols et al. 1979; Serena-Lungarotti et al. 1979; de Grouchy and Turleau 1982). All concern dysmorphic and mentally retarded children but none of them have breakpoints similar to those in our patient. In all carriers of a deletion of q21, a deletion of at least a part of the neighbouring bands, q14 and q22, is associated. Generally, imbalanced autosome abnormalities, especially deletions, cause an abnormal phenotype and mental defi- ciency in their carriers. Nevertheless, Friedrich and Nielsen (1974) reported two cases of deletions associated with a nor-