Methylation of the DXS255 hypervariable locus 5′ CCGG site may be affected by factors other than X-chromosome activation status

An update on clonality, cytokines, and viral etiology in Langerhans cell histiocytosis

Many etiologies have been proposed for Langerhans cell histiocytosis (LCH). Recent scientific studies have clearly provided new insights into the etiology and pathogenesis of the disease. The possible role of viruses has not been completely negated, but no viral genomes have been consistently detected in LCH lesions. Other studies do not indicate that LCH arises from a primary defect in the immune system, although altered immune responses and immune dysfunction may play a role in the pathophysiology of the disease. Definitive results have been gained from molecular studies of clonality, however. These have definitively established that LCH is a clonal histiocytic disease rather than a reactive polyclonal disorder.

Pathogenetic Aspects of Myelodysplastic Syndromes

The myelodysplastic syndromes (MDS) are acquired clonal disorders of the bone marrow. They were clearly defined in morphological terms by the French-American-British (FAB) group in 1982, as five conditions each with their own diagnostic criteria, but with the shared characteristics of ineffective blood cell production in one or more cell line, morphological dysplasia and a variable propensity to evolve into acute myeloid leukaemia (AML). In clinical practice patients typically present in old age with macrocytic anaemia, cytopenias, monocytosis and accumulation of marrow blast cells leading in time to fatal bone marrow failure or AML. To date treatment is unable to alter the natural history of MDS except in those few individuals who are able to undergo allogeneic progenitor cell transplantation.

Clonality Analysis of Benign Parathyroid Lesions by Human Androgen Receptor (HUMARA) Gene Assay

Benign conditions of the parathyroid gland have been classified as adenomas and hyperplasias. These entities however are difficult to distinguish when only a single gland is enlarged. Adenomas are defined as neoplastic clonal growths whereas hyperplasias are considered to be reactive processes of polyclonal origin. In order to analyze the clonal pattern of these lesions, we have studied hyperplasias and adenomas of parathyroid glands from women by the human androgen receptor (HUMARA) assay, a recently reliable and highly-lnformative technique based on the X-chromosome inactivation pattern in females. Samples consisted of formalin-fixed as well as frozen tissues. Informativeness with HUMARA marker was 87% (13/15 cases). All hyperplasias (5/5) and 6/8 adenomas yielded polyclonal results, since two alleles of similar intensity appeared when the lesion was HpaIl-digested. Two parathyroid adenomas had a loss of one X-alIeIe for the HUMARA gene and they were interpreted as monoclonal. These results show that parathyroid hyperplasias and adenomas, considered as multigland or monogland involvement diseases respectively, may be both polyclonal in origin, and that only a small subset of adenomas is found to be clonal. Consequently, clonality analysis cannot allow a clear distinction between these two entities as classically diagnosed. A different approach should be considering hyperplasia or adenoma when a polyclonal or monoclonal result has been obtained by clonality analysis.

Hypermethylation of the M27beta (DXS255) locus in chronic B-cell leukaemia

We have investigated the methylation status of the M27beta (DXS255) locus in 21 female patients with chronic B-cell leukaemia and in 20 normal controls. DNA was digested with Pst1 and then with the methylation sensitive enzyme HpaII and probed with the M27beta probe. Eight patients (38%) showed hypermethylation of the M27beta locus which was not seen in any of the normal controls. Hypermethylation of the M27beta locus has also been found in acute myeloid leukaemia, acute lymphocytic leukaemia and lymphoma, suggesting that hypermethylation of the M27beta locus is associated with the leukaemic process.

Clonality analysis in tumours of women by PCR amplification of X-linked genes

Modifications have been made to two polymerase chain reaction (PCR) methods for clonality analysis based on the inactivation patterns of two highly polymorphic X-linked genes encoding the androgen receptor (AR) and monoamine oxidase A (MAOA). These methods have been used to examine the clonal nature of frozen tissues from 42 tumours and 25 non-tumour controls from female subjects. Unbalanced inactivation patterns of the genes, which indicate monoclonality, were frequently observed in tumours of heterozygous (informative) cases (18/35 = 51.4 per cent for the AR gene, 9/30 = 30 per cent for the MAOA gene, and 21/38 = 55.2 per cent for both). Among 23 informative non-tumour controls, only one (4.3 per cent), a reactive lymph node, showed skewing in the AR gene. Successful detection of monoclonality was found to depend on the proportion of tumour cells in the tissues examined. None of the AR or MAOA informative cases containing less than 50 per cent of tumour cells showed imbalance in inactivation patterns. With more than 50 per cent of tumour cells in the samples, 66.6 per cent (18/27) of AR and 39.1 per cent (9/23) of MAOA informative cases showed allelic imbalance, with a combined frequency of 72.4 per cent (21/29) of both genes. Our results demonstrate that the methods described are useful for clonal analysis of tissue samples from female patients.

Mutation analysis of the pyruvate dehydrogenase E1 alpha gene in eight patients with a pyruvate dehydrogenase complex deficiency

Most of the mutations causing deficiency of the pyruvate dehydrogenase (PDH) complex are in the X-linked E1 alpha gene. We have developed a rapid screening method for the detection of mutations in this gene using reverse transcription of total RNA, polymerase chain reaction amplification of the whole coding region of the gene and single-strand conformation polymorphism (SSCP) analysis. With this method, we studied eight patients with a PDH complex deficiency, using cultured fibroblasts. In all patients, aberrant SSCP patterns were found and, after sequencing of the corresponding fragments, we were able to identify six new mutations and two mutations already described previously. The mutations are point mutations leading to amino acid substitutions (5) and direct repeat insertions (3). The presence of the mutations was confirmed in genomic fibroblast DNA. The 4 female patients were shown to carry both a normal and a mutated E1 alpha gene.

A novel clonality assay for the mouse: application to hepatocellular carcinomas induced with diethylnitrosamine

A polymerase chain reaction-based clonality assay was developed for mouse tumors and cellular proliferations of the mouse. This assay was based on a polymorphism of the phosphoglucokinase-1 (Pgk-1) gene on the X chromosome between two different mouse subspecies and the different methylation patterns of active and inactive X chromosomes. All 15 tumor cell lines examined showed one of the two allelic bands on gel electrophoresis, which is consistent with the theory that tumor cell lines are monoclonally derived. This suggests that the Pgk-1 system is useful for clonality studies that will give insight into cancer development. With this method, nine hepatocellular carcinomas were examined, and eight showed monoallelic patterns. The remaining tumor exhibited a biallelic pattern, which is suggestive of polyclonal origin; however, other possibilities are discussed.

Changing p53 mutations with the evolution of chronic myeloid leukaemia from the chronic phase to blast crisis

The frequent involvement of chromosome 17p abnormalities in the progression of chronic myeloid leukaemia (CML) led us to investigate the involvement of the p53 tumour suppressor gene located on chromosome 17p. We analysed 31 samples from four patients sequentially, and 16 patients in blast crisis only, using single stranded conformational polymorphism (SSCP) analysis of exons 5-8, followed by cloning and sequencing. The sequential samples ranged from diagnosis through to late disease. We found that 15% of our blast crisis samples had p53 abnormalities. In our sequential studies we found two of the four patients analysed in more detail had p53 mutations in the late chronic phase of disease (11 and 5 months prior to blast crisis becoming apparent). These chronic phase mutations differed from the p53 abnormalities found in the blast crisis samples from these patients. One patient also had the same chronic phase mutation at post bone marrow transplant relapse. Our results suggest that, in some cases, sequential investigations through CML disease progression of p53 mutations and other oncogenes/proto-oncogenes may provide early indications of the routes of disease progression to blast crisis.

X-chromosome methylation in manifesting and healthy carriers of dystrophinopathies: concordance of activation ratios among first degree female relatives and skewed inactivation as cause of the affected phenotypes

The X-chromosome activity states of 11 manifesting carriers of dystrophinopathies, all with normal karyotypes, were estimated by restriction fragment length polymorphism (RFLP)-methylation analysis with the probes M27 beta (DXS255), p2-19(DXS605) and pSPT/PGK (PGK1) to test the role of skewed X-inactivation ratios as the cause of their affected phenotypes. In eight cases preferential inactivation of the putative X chromosome carrying the normal dystrophin allele in > or = 90% of their peripheral lymphocytes was observed, two cases showed non-apparent deviant ratios (60:40 and 70:30) from the theoretically expected values around the mean of 50% and in one case the three markers employed yielded no information. The analysis of the X-inactivation ratio in six mother-daughter pairs, all non-manifesting Duchenne muscular dystrophy (DMD) carriers, and in the close female relatives of the patients showed: (a) neither of the two X chromosomes was preferentially inactivated with respect to their parental origin; (b) a high concordance among the activation ratios of mothers and daughters, a result difficult to explain just in terms of random X-chromosome inactivation.

Refractory anaemia with preleukaemic polyclonal haemopoiesis and the emergence of monoclonal erythropoiesis on disease progression

We describe a young woman with a myelodysplastic syndrome (MDS) of the type refractory anaemia (RA) which remained stable for 11 years and then underwent rapid progression manifested by bone marrow failure with the emergence of a complex clonal cytogenetic abnormality. Peripheral blood granulocytes, mononuclear cells and bone marrow erythroblasts were all polyclonal by X-inactivation analysis detected by the probe M27B during the preleukaemic phase. On disease progression, bone marrow erythroblasts developed an extremely skewed monoclonal pattern of X-inactivation. In some cases of MDS, therefore, polyclonal haemopoiesis can be detected for a considerable time during the preleukaemic phase and we report the demonstration of bone marrow erythroblasts changing from a polyclonal to a monoclonal pattern on disease progression.

Langerhans'-cell histiocytosis (histiocytosis X)--a clonal proliferative disease

BACKGROUND

The lesions of Langerhans'-cell histiocytosis (histiocytosis X), a proliferative histiocytic disorder of unknown cause, contain histiocytes similar in phenotype to dendritic Langerhans' cells. The disease ranges in severity from a fatal leukemia-like disorder to an isolated lytic lesion of bone. Intermediate forms of the disease are usually characterized by multiorgan involvement, diabetes insipidus, and a chronic course.

METHODS

To determine whether Langerhans' histiocytosis is a polyclonal reactive disease or a clonal disorder, we used X-linked polymorphic DNA probes (HUMARA, PGK, M27 beta[DXS255], and HPRT) to assess clonality in lesional tissues and control leukocytes from 10 female patients with various forms of the disease. Lymphoid clonality was also assessed by analysis of rearrangements at immunoglobulin and T-cell-receptor gene loci.

RESULTS

The HUMARA assay detected clonal cells in the lesions of 9 of the 10 patients: 3 patients had acute disseminated disease, 3 had unifocal disease, and 3 had intermediate forms. The percentage of clonal cells closely approximated the percentage of CD1a-positive histiocytes in each lesion. Clonality was also confirmed in two of nine cases with the PGK or M27 beta probe. Extreme constitutional lyonization precluded assessment of clonality in the 10th case. Lymphoid clonality was ruled out in all cases.

CONCLUSIONS

The detection of clonal histiocytes in all forms of Langerhans'-cell histiocytosis indicates that this disease is probably a clonal neoplastic disorder with highly variable biologic behavior. Thus, genetic mutations that promote clonal expansion of Langerhans' cells or their precursors may now be identified.

Oligoclonal B-cell leukemia characterized by spontaneous cell division and telomere association

Cytogenetic analysis of unstimulated cultures from a female patient with chronic B-cell leukemia (CLL) revealed three cytogenetically distinct clones, suggesting that the patient's leukemia was oligoclonal. Immunoglobulin heavy chain gene rearrangement studies revealed 1 germline and 4 rearranged bands, indicative of an oligoclonal leukemic population. Further evidence of oligoclonality was provided by X-linked RFLP studies. This is the first report of oligoclonality in CLL demonstrated by cytogenetic, immunoglobulin gene rearrangement, and X-chromosome inactivation studies. In addition to oligoclonality, the patient's leukemic cells exhibited telomere association, a Robertsonian translocation, and clonal evolution, suggesting an underlying genomic instability.