A functional marker centromere with no detectable alpha-satellite, satellite III, or CENP-B protein: activation of a latent centromere?

We report the investigation of an unusual human supernumerary marker chromosome 10 designated "mar del(10)." This marker is present together with two other marker chromosomes in the karyotype of a boy with mild developmental delay. It has a functional centromere at a primary constriction and is mitotically stable. Fluorescence in situ hybridization (FISH) using alpha-satellite and satellite III DNA as probes failed to detect any signal at the primary constriction site. CENP-B protein could not be demonstrated, although the presence of at least some centromeric proteins was confirmed using a CREST antiserum. Consideration of these and other cytogenetic and FISH results supports a mechanism of formation of the mar del(10) chromosome involving the activation of a latent intercalary centromere at 10q25.

Confirmation of trisomy 22 in two cases using chromosome painting: comparison with t(11;22)

We present a nonmosaic case of trisomy 22 in a liveborn, abnormal infant and a second case of a fetus who died in utero. Both have been verified cytogenetically and confirmed by in situ hybridisation with a centromeric alphoid probe and chromosome painting. The accuracy of the combined cytogenetic and molecular cytogenetic approaches in the karyotype determination is highlighted by comparison with a case showing partial translocation of chromosome 22 in t(11;22) (q23;q11).

Absence of satellite III DNA in the centromere and the proximal long-arm region of human chromosome 14: analysis of a 14p- variant

Cytogenetic methods and molecular probes derived from the centromere and short arm of chromosome 14 were used to investigate the structural properties of a chromosome 14 variant. Results of GTL, CBG, Ag-NOR, and non-banded Giemsa staining of the chromosomes suggested the complete absence of the short arm and possibly a large part of the centromere. Negative in situ hybridisation with an alpha satellite III probe confirmed the absence of the arm; the detection of normal amounts of alpha satellite DNA, however, indicated retention of the centromeric domain. The natural occurrence of a human acrocentric variant lacking a short arm was thus established. Within the detection limits of the methods used, the results demonstrate that satellite III DNA is not essential for normal centromeric activity and allow us to exclude the presence of this satellite DNA within the centromere and proximal long-arm region of human chromosome 14.

The importance of further cytogenetic and molecular investigation of acrocentric variants: justification by presentation of a case [t(8;14)(q24;p11)]

On routine chromosome analysis a moderately retarded 18-year-old man was found to have an unusual short arm on one chromosome 14. With GTL-banding this chromosome showed an enlarged short arm with no evident secondary constriction. Negative CBG-banding of the short arm suggested the possibility of a translocation involving euchromatin. Interpretation of the abnormality as an unbalanced translocation relied on chromosome analysis using GTL-, CBG-, and Ag-NOR-banding of the proband's phenotypically normal mother, who was found to be carrying a balanced translocation involving chromosomes 8 and 14. In situ hybridization of sequences known to map to the short arm of chromosome 14 confirmed the interpretation and established that the breakpoint was within p11. The patient, whose karyotype is 46,XY, -14, +der(14)t(8;14)(q24.1;p11), is trisomic for the terminal end of the long arm of chromosome 8. The patient's clinical features are described and compared with those reported in patients trisomic for this region. This study demonstrates the importance of using a number of different banding techniques in conjunction with in situ hybridization for the investigation of morphologically unusual acrocentric short arm variants seen at routine diagnosis.

Two forms of ring 13 in a child with rhabdomyosarcoma

Mosaicism for two forms of ring 13 was found in a child with embryonal rhabdomyosarcoma of the bladder, minor anomalies, and developmental delay. Her chromosome constitution was 46,XX,r(13)(p11q34)/46,XX,r del(13)(p11q14). Both cell lines were present in lymphocytes and fibroblasts. The cell line with the smaller ring chromosome predominated in both tissues. The child's manifestations reflect the presence of both cell lines.

Five cases demonstrating the distinctive behavioural features of chromosome deletion 17(p11.2 p11.2) (Smith-Magenis syndrome)

Children with hyperactivity and self-destructive behaviour present a difficult problem for parents and paediatricians. The syndrome described by Smith and Magenis is due to a deletion on the short arm of chromosome 17: del(17)(p11.2 p11.2). Clinical manifestations include brachycephaly and a flat mid-face; brachydactyly; short, broad hands; mental retardation; and aberrant behaviour, including hyperactivity. We report on five children, and review the literature on a newly recognised syndrome in which the behaviour manifestations may precede and often overshadow the learning disabilities and unusual appearance. In addition, we have found sleep disturbance to be a major feature in our patients.

Fragile X testing in a diagnostic cytogenetics laboratory

Chromosome results obtained from 1012 patients referred with developmental delay without known cause within the three years 1985 to 1987 are reported. G banding analysis and assessment of 70 cells for fragile X gave abnormal results in 84 cases: fragile X in 31 patients and other abnormalities in 53 patients. A further 16 sibs expressing the fragile X were detected in family studies originating from the 31 index cases. This yield justifies continuation of procedures which detect both fragile X and subtle chromosomal abnormalities in these patients.

Non C-banding variants in some normal families might be homogeneously staining regions

Three families are reported showing transmission of a previously described variant, which is not associated with any clinical abnormality. The variant involves additional material at the band 9p12, which shows homogeneous staining of intermediate density with GTL- and RBG-banding, and negative staining with CBG-banding. The region stains positively with Feulgen stain. In situ hybridization with total genomic human DNA, cloned alpha satellite, satellite III, and ribosomal DNA all show no hybridization to the 9p12 variant. Two members of one of the families show the largest 9p12 variant yet reported; two other carriers in this family have inherited a variant of decreased size. It is suggested that the 9p12 variants are homogeneously staining regions. Using the ISCN three-letter convention, this variant could be described as hsr(9)(p12).

Complex chromosome rearrangements involving chromosomes 1;3 and 2;3 in two abnormal children

Complex chromosome rearrangements (CCR) involving multiple breaks in two chromosomes are rare. The detection of a four-break apparently balanced rearrangement involving chromosomes 1 and 3 in a child with developmental delay led us to reanalyse, using prometaphase banding, another complex two-chromosome rearrangement in a previously reported case (Fitzgerald 1974). The relationship between clinical abnormalities and apparently balanced rearrangements is discussed.

Duplication of a small segment of 5p due to maternal recombination within a paracentric shift

Duplication of chromosome sub-bands 5p14.3 and 5p15.1 in a child resulted in mild mental retardation, apparently without other abnormalities. The duplicated region arises from recombination within a directly inserted segment following a shift within the short arm of the maternal chromosome 5 homologs.

Chromosome deletion at 11q23 in an abnormal child from a family with inherited fragility at 11q23

A neonate with clinical features of the 11q23 deletion syndrome was apparently mosaic with the dominant cell line showing deletion of the chromosomal segment 11q23.3 to 11qter. The presence of a few lymphocytes with a normal karyotype indicates post-zygotic deletion of chromosome 11. The mother and brother of the propositus show folate-sensitive fragility at band 11q23.3. This case indicates in vivo deletion at a folate-sensitive fragile site.