I. Voiculescu

Familial ring (20) chromosomal mosaicism

SummaryRing (20) chromosomal mosaicism defined by two cell lines (one normal and the other with the ring) has been demonstrated in lymphocyte and fibroblast cultures from three members of a family through two generations. Two carriers of the ring chromosome were affected and showed the typical signs of r(20) syndrome including mental retardation, microcephaly, behavioral disorders, and epilepsy. The epilepsy is characterized by complex partial seizures sometimes evolving secondarily into generalized tonic-clonic seizures and is poorly controlled by or resistant to medical treatment. The mother of the two patients, also a carrier of ring (20) chromosomal mosaicism, was clinically and phenotypically normal and did not exhibit any signs of epilepsy. Lymphocyte and fibroblast cultures from the most severely affected sib, the proband, contained the highest percentage of cells with ring (20) chromosome and revealed the greatest instability of the ring. Though it is assumed that the ring (20) chromosome arose from terminal breakage and reunion in both arms, no loss of genetic material could be documented cytogenetically. Yet the question arises of how ring chromosomal mosaicism can be passed on. One explanation might be that a chromosome 20 predisposed to terminal lesions or breaks is transmitted from the mother to her offspring. Inherited instability of this type might lead to de novo formation of the ring.

A simplified method of demonstrating Giemsa-Band pattern in human chromosomes

SummaryA simplified method of demonstrating multiple chromosome banding pattern is described. In this method, it is assumed that differential denaturation is the basis of the pattern.ZusammenfassungEine vereinfachte Methode zur Darstellung multipler Giemsa-Bandenmuster auf Chromosomen wird beschrieben. Als Grundlage für die Entstehung der Banden wird bei dieser Methode eine differentielle Denaturierung der DNS angenommen.

Replication banding studies in two cyprinid fishes

The use of the in vivo 5-bromodeoxyuridine (BrdU) incorporation technique made it possible to induce highly reproducible replication bands of the RBA type in two species of the order Cypriniformes (Teleostei), Rutilus rutilus and Scardinius erythrophthalmus. This allowed unequivocal identification of each individual chromosome by its banding pattern and the preparation of species specific karyotypes. Comparison of RBA-banded karyotypes of these two closely related fish species revealed that the majority of the chromosomes could be homoeologized either directly, or by assuming paracentric or pericentric inversions.

Trisomy 22 in a newborn with multiple malformations

SummaryA case of complete trisomy 22 in live-born female child with multiple malformations is reported. The karyotype of the index patient had 46 chromosomes, with one chromosome 22 missing and one supranumerary metacentric chromosome. Different banding methods and in situ hybridization revealed that the extra chromosome consists of the long arms and a part of the short arms of two chromosomes 22. Our report supplies further proof that a fetus with complete trisomy 22 can occasionally survive to term, but the condition is not compatible with life over a long period.

De novo isochromosome 18p in two patients: cytogenetic diagnosis and confirmation by chromosome painting

This report concerns two patients with clinical features typical for tetrasomy 18p syndrome. Chromosomal analysis revealed a male karotype in both cases, with an additional small metacentric marker chromosome, putatively an i(18p). Fluorescent in situ hybridization with a chromosome 18‐specific paint confirmed that the marker chromosome consisted of chromosome 18 material in both cases.

Familial pericentric inversion of chromosome 12

SummaryA pericentric inversion in one of the chromosomes 12, found in two families living in the same region, is deseribed. This inversion was detected during routine chromosomal analysis in two separate laboratories. The breakpoints were at 12p112 and 12q13. The inverted segment represented approximately 20% of the length of chromosome 12. Twenty nine descendants of carriers of the inversion were investigated, and the inversion was present in 23 of them. The other six descendants showed a normal karyotype. After correction for sample bias with the single selection scheme, a segregation ratio of 3:1 was estimated, indicating that the inverted chromosome 12 was preferentially transmitted. All the carriers of the inversion were phenotypically normal, without noticeable fertility disturbances.

Karyotyp und Heterochromatinmuster des rumänischen Hamsters (Mesocricetus newtoni)

In the Romanian hamster (2n=38) a number of whole chromosome arms is heterochromatic. This offers the opportunity to test the effect of some recently developed differential staining techniques upon heterochromatin. It is shown that the late replicating segments are stained by the C-banding technique. A method for exclusively demonstrating centromeric heterochromatin is described. With this, only 8 autosome pairs and the X-chromosome show centric heterochromatin. There is a good agreement between the multiple banding pattern produced by fluorescent and Giemsa stain.

A retrospective CISS hybridization analysis of a case with de novo translocation t(18;22) resulting in an 18p- syndrome.

Voiculescu I, Toder R, Back E, Osswald P, Schempp W. A retrospective CISS hybridization analysis of a case with de novo translocation t(18;22) resulting in an 18p—syndrome.

Homozygous condition for a BrdU-requiring fragile site on chromosome 12

SummaryA rare BrdU-sensitive fragile site, designated FRA12C*RQ24.2 has a relatively high frequency in the normal population. It can be demonstrated in a heterozygous and homozygous condition. There is no evidence that a phenotypic abnormality is associated with the expression of this site. A comparison with the fragile site FRA10B*RQ25.2 has revealed common features with FRA12C*RQ24.2.

A BrdU-requiring fragile site on chromosome 12

SummaryA BrdU-requiring fragile site, fra(12)(q24.2), on human chromosome 12 of some individuals is reported. This fragile site is inherited in a Mendelian codominant fashion and does not seem to be associated with any physical or mental abnormality in carriers. It was mostly observed as a chromatid gap: no acentric fragments, triradials or deleted chromosomes were found. The fra(12)(q24.2) was expressed in 34%–48% of metaphases in lymphocyte cultures from carriers when BrdU and FdU were added 6.5 h before harvest, while the expression ranged between 5% and 20% when the cultures were treated with BrdU alone. The fra(12)(q24.2) represents the second BrdU-requiring rare fragile site described on human chromosomes.