Myelodysplastic syndrome in a kindred with ins(16) (p11.2)

Directly transmitted unbalanced chromosome abnormalities and euchromatic variants

In total, 200 families were reviewed with directly transmitted, cytogenetically visible unbalanced chromosome abnormalities (UBCAs) or euchromatic variants (EVs). Both the 130 UBCA and 70 EV families were divided into three groups depending on the presence or absence of an abnormal phenotype in parents and offspring. No detectable phenotypic effect was evident in 23/130 (18%) UBCA families ascertained mostly through prenatal diagnosis (group 1). In 30/130 (23%) families, the affected proband had the same UBCA as other phenotypically normal family members (group 2). In the remaining 77/130 (59%) families, UBCAs had consistently mild consequences (group 3). In the 70 families with established EVs of 8p23.1, 9p12, 9q12, 15q11.2, and 16p11.2, no phenotypic effect was apparent in 38/70 (54%). The same EV was found in affected probands and phenotypically normal family members in 30/70 families (43%) (group 2), and an EV co-segregated with mild phenotypic anomalies in only 2/70 (3%) families (group 3). Recent evidence indicates that EVs involve copy number variation of common paralogous gene and pseudogene sequences that are polymorphic in the normal population and only become visible at the cytogenetic level when copy number is high. The average size of the deletions and duplications in all three groups of UBCAs was close to 10 Mb, and these UBCAs and EVs form the "Chromosome Anomaly Collection" at http://www.ngrl.org.uk/Wessex/collection. The continuum of severity associated with UBCAs and the variability of the genome at the sub-cytogenetic level make further close collaboration between medical and laboratory staff essential to distinguish clinically silent variation from pathogenic rearrangement.

Euchromatic variant 16p+. Implications in prenatal diagnosis

BACKGROUND

Euchromatic imbalances at the cytogenetic level are usually associated with phenotypic consequences. Among the exceptions are euchromatic variants of chromosome 16 (16p+) with normal phenotype. There is a growing list of euchromatic duplications and deletions involving both G-positive and G-negative bands that seem to be phenotypically neutral, but these euchromatic variants are rare.

OBJECTIVE

The aim of this report is to describe a new familial case of euchromatic variant 16p+ and to emphasise the misinterpretation of these rare euchromatic variants particularly when ascertained at prenatal diagnosis.

METHODS AND RESULTS

Fluorescence in situ hybridisation with clone RP11-261A7 showed an amplified signal in the larger chromosome 16. This clone contains FLJ43855 gene, similar to sodium- and chloride-dependent creatine transporter.

CONCLUSION

So, this 16p+ variant that involves amplification of pseudogenetic sequences is considered a polymorphism in normal individuals.

Constitutional chromosome aberrations as pathogenetic events in hematologic malignancies

A predisposition to tumor development is associated with some constitutional chromosomal abnormalities. Investigations of families with an apparent hereditary cancer and constitutional chromosome rearrangements have led to the molecular identification of tumor suppressor genes. Under the somatic mutation theory for the development of cancer, two mutational events are required. The first step may be a constitutional event and the second an acquired genetic mutation. Cytogenetic studies were performed on 5633 bone marrow specimens from patients with hematologic malignancies from a single institution. Fifty cases of constitutional chromosome aberrations were detected. Data collected from the literature and from our series are reviewed and compared with the incidence of specific constitutional chromosome aberrations in the newborn population. Possible mechanisms that may predispose individuals with constitutional chromosome aberrations to the development of a hematologic malignancy are reviewed.

Euchromatic 16p+ heteromorphism: first report in North America

A heteromorphism of the short arm of 16 (16p+) was discovered in 2 unrelated infants. By G banding, the euchromatic variant appears as a light and a medium dark band just distal to the centromere. This results in an increase of the short arm by about 1/3. The same variant was present in the normal father and the normal paternal grandmother in one family and mildly retarded mother in the 2nd family. The anomalies of the 2 infants are not similar and are apparently unrelated to the 16p+ variant. Though the discovery of such euchromatic variants is highly significant for clinical diagnosis, their genetic significance and mode of origin remain to be elucidated.

Clonal karyotype abnormalities and clinical progress in the myelodysplastic syndrome

Clonal karyotype abnormalities in 124 patients with myelodysplastic syndrome are reviewed. 36% of patients had abnormalities at referral, the most common being 5q-, +8 and lesions of chromosomes 7 and 20. Reduced survival was associated with the presence of either single or multiple clonal abnormalities at referral, abnormalities of chromosome 7 or 8 (either alone or with other lesions) and exclusively abnormal metaphases. The presence of 5q- alone did not appear to affect survival. Sequential studies were carried out in 77 patients of whom 12 showed karyotypic evolution. Reduced survival was observed in patients with an evolving karyotype but appeared to be due almost entirely to evolution in those patients whose initial karyotype was normal. Leukaemic transformation occurred more commonly in patients with an abnormal karyotype, particularly those with multiple abnormalities, and in patients with an evolving karyotype. Although the first appearance of an abnormal karyotype or an apparent evolution are important phenomena, it is probable that in some cases they merely represent expansion of a previously existing clone that has escaped detection. The distinction between true karyotypic evolution or clonal expansion and statistical variations due to small sample size and variability of samples may be difficult but needs to be taken into account in considering clinical significance.

Differences in bone marrow cytogenetic characteristics between treated and untreated myeloma

Clonal karyotypic abnormalities in myelomatosis at initial diagnosis have been widely studied, but little data are available on the karyotypic status following treatment. We have studied bone marrow (BM) from 17 cases of untreated myelomatosis at initial diagnosis and from a further 29 cases who had received chemotherapy with regimens containing alkylating agents. At the time of study all previously treated cases had been off treatment for at least 152 days, had a paraprotein level in plateau phase, had a BM with less than 4% blasts, and in 28 of these 29 cases had less than 20% BM plasma cells. Two cases had more than 15% BM ringed sideroblasts; one other case was transfusion dependent. Clear differences in cytogenetic characteristics between the two groups were seen. At initial diagnosis clonal karyotypic abnormalities were observed in six of 11 accessible cases. All had hyperdiploid clones (of 49-54 chromosomes) and showed characteristic involvement of chromosomes 3, 5, 7, 9, 11, 15, 19 and 21. Additional structural rearrangements were present in only two of these cases. Following treatment, clonal abnormalities were seen in 10 of 25 assessible cases, of which only two showed hyperdiploidy (one with a hyperdiploid line, one with an additional derived chromosome). The remaining eight showed hypodiploid or pseudodiploid lines, and seven of these showed complex karyotypes with multiple rearrangements particularly affecting chromosomes 1, 2, 3, 6 and 7. After a minimum follow-up of 16 months, only four of these 10 cases (40%) remain alive compared with 12 of 15 (80%) with a normal karyotype after treatment (P = 0.03). No correlation was observed between the presence of an abnormal karyotype and the total dose or timing of previous therapy, though cases with an abnormal karyotype tended to have received treatment for longer (790 +/- 166 days) than cases with a normal karyotype (486 +/- 50 days). It is not clear whether the ploidy difference between the two groups represents a change in the disease state due to treatment or a direct effect of treatment itself.