Following a previous collaborative study (Fraccaro et al. 1980), 20 new cases of 11q;22q translocation are described. Twelve families were ascertained through an unbalanced carrier of the translocation and eight cases were ascertained as balanced carriers. A segregation analysis was performed on the 110 families so far published. It was concluded that the 11q;22q translocation is a relatively frequent event, and that all the cases thus far reported might have the same breakpoints at 11q23.3 and 22q11.2. The translocation seems to be independent of environmental factors and it seems to have a low rate of mutation as indicated by the scarcity of de novo cases. The new data confirmed that only one type of unbalanced karyotype (47,XX or XY+der(22)t(11;22)(q23.3;q11.2)) is found among the offspring of the translocation carriers. The minimal overall recurrence risk for an unbalanced translocation was estimated to 2%. There was no difference between the recurrence risks for male and female balanced carriers, while the trend was confirmed of an excess of female balanced carriers among the phenotypically normal offspring of the t(11;22) female carriers.

Objective We surveyed the datasheets of 29 laboratories concerning prenatal diagnosis of de novo apparently balanced chromosome rearrangements to assess the involvement of specific chromosomes, the breakpoints distribution and the impact on the pregnancy outcome.Method By means of a questionnaire, data on 269.371 analyses performed from 1983 to 2006 on amniotic fluid, chorionic villus and fetal blood samples were collected.Results A total of 246 balanced anomalies were detected at frequencies of 72% for reciprocal translocations, 18% for Robertsonian translocations, 7% for inversions and 3% for complex chromosome rearrangements. The total frequencies of balanced rearrangements were 0.09%, 0.08% and 0.05% on amniotic fluid, chorionic villus and fetal blood samples.Conclusion A preferential involvement of chromosomes 22, 7, 21, 3, 9 and 11 and a less involvement of chromosomes X, 19, 12, 6 and 1 was observed. A nonrandom distribution of the breakpoints across chromosomes was noticed. Association in the location of recurrent breakpoints and fragile sites was observed for chromosomes 11, 7, 10 and 22, while it was not recorded for chromosome 3. The rate of pregnancy termination was about 20%, with frequencies decreasing from complex chromosomal rearrangements (33%), reciprocal translocations (24%) to inversions (11%) and Robertsonian translocations (3%).

We report on a newborn girl with a terminal deletion of the long arm of chromosome 10: del (10)(pter----q26). The phenotypic manifestations are compatible with those of the previously reported cases. In addition, the association with abnormalities of the urinary tract is reported for the first time. A clinical and neurodevelopmental follow-up is described up to age 18 months.

Purpose: We evaluated the experiences of 19 Italian laboratories concerning 241 small supernumerary marker chromosomes (sSMCs) with the aim of answering questions arising from their origin from any chromosome, their variable size and genetic content, and their impact on the carrier's phenotype. Methods: Conventional protocols were used to set up the cultures and chromosome preparations. Both commercial and homemade probes were used for the fluorescent in situ hybridization analyses. Results: A total of 113 of the 241 sSMCs were detected antenatally, and 128 were detected postnatally. There were 52 inherited and 172 de novo cases. Abnormal phenotype was present in 137 cases (57%), 38 of which were antenatally diagnosed. A mosaic condition was observed in 87 cases (36%). In terms of morphology, monocentric and dicentric bisatellited marker chromosomes were the most common, followed by monocentric rings and short-arm isochromosomes. The chromosomes generating the sSMCs were acrocentric in 132 cases (69%) and non-acrocentric chromosomes in 60 cases (31%); a neocentromere was hypothesized in three cases involving chromosomes 6, 8, and 15. The widespread use of molecular cytogenetic techniques in diagnostic laboratories has improved diagnostic quality, especially in prenatal cases. However, one of the few major problems remaining is the identification of the nature and origin of small supernumerary marker chromosomes (sSMCs).sSMCs display a wide range of morphology and occur at highly variable incidence, 1,2 thus giving rise to considerable problems in genetic counseling, particularly during prenatal testing. Only the combined use of conventional and molecular

Seven patients are described who have some or all of the symptoms of Prader-Willi syndrome. They were ascertained by varying criteria starting either from the clinical picture or from the identification of a chromosome abnormality involving the proximal portion of the long arm of chromosome 15. The chromosome abnormalities consisted of two balanced translocations (15;18 and 8;15), three unbalanced ones (15;18, 15;19, and 9;15), and one interstitial deletion of bands 15q11 and q12. The seventh case had an unidentified extra chromosome. These data and a review of the literature led to the conclusion that deficiency, transposition, and even duplication of the region(s) 15q11-q13 may all result in a syndrome which is identifiable with or similar to the Prader-Willi syndrome.