Trisomy Disorders

Trisomy 6 Mosaicism

Posted on: October 30, 2008

 

Chromosome 6, Partial Trisomy 6q

Important

It is possible that the main title of the report Chromosome 6, Partial Trisomy 6q is not the name you expected. Please check the

synonyms listing to find the alternate name(s) and disorder subdivision(s) covered by this report.

Synonyms

  • Chromosome 6, Trisomy 6q2
  • Trisomy 6q Syndrome, Partial
  • 6q+ Syndrome, Partial
  • Trisomy 6q, Partial
  • Distal Trisomy 6q
  • Duplication 6q, Partial
  • Distal Duplication 6q

Disorder Subdivisions

  • None

General Discussion

Chromosome 6, Partial Trisomy 6q is an extremely rare chromosomal disorder in which a portion of the 6th chromosome (6q) is present three times (trisomy) rather than twice in cells of the body. Associated symptoms and findings may vary in range and severity from case to case. However, many affected infants and children have slow physical development (growth retardation); mental retardation; malformations of the skull and facial (craniofacial) region; an unusually short, webbed neck; abnormal bending (flexion) or extension of certain joints in fixed postures (joint contractures); and/or other physical abnormalities. In most cases, Chromosome 6, Partial Trisomy 6q has been the result of a balanced translocation in one of the parents.

WebMd/Nord

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+6 or trisomy 6

Clinics and Pathology

Note Trisomy 6 (+6) has been reported as the sole cytogenetics aberration in 14 cases of acute myeloid leukaemia (AML) and five cases of myelodysplastic syndrome. Three out of four AML patients with +6 in one series showed AML-M1 morphology and expression of stem cell antigen CD34 on the leukaemic blasts, suggesting that +6 may be associated with a more primitive form of AML. Nevertheless, other reported cases represent a broader spectrum of AML and it is therefore premature to draw conclusion as to whether special morphological and phenotypic features exist in AML with +6.

Intriguingly, +6 as the sole cytogenetics abnormality have been reported in 12 cases of haematological disorders characterized by peripheral blood cytopenia and hypoplastic bone marrow. Among the 12 cases, eight cases showed dysplastic change in the haemopoietic cells, whereas four did not. In two cases of aplastic anaemia with dyserythropoiesis and +6, FISH showed +6 in erythroid as well as myeloid cells, suggesting involvement of an early haemopoietic progenitor cell. The overall survival ranges from 9 – 48 months. In all cases, normal cells without +6 are present, and the percentage of metaphases with +6 ranges from 6.9% to 85%. It is questionable whether such cases should be classified as hypoplastic MDS, based on clonal cytogenetic change of +6, or aplastic anaemia. The pathogenesis of aplastic anaemia is heterogeneous. While an immunological basis for this disorder is established based on response to immunosuppressive therapy, there is also evidence for clonal nature resulting from damage to the haemopoietic stem cell compartment. Indeed clonal chromosomal abnormalities are reported in otherwise typical aplastic anaemia. Furthermore, aplastic anaemia evolving into acute leukaemia is well documented. This is exemplified by the development of AML in a case of aplastic anaemia with +6 and no dysplasia 15 months after initial diagnosis. Although patients with +6 and marrow aplasia were uniformly non-responsive to treatments by steroids and anti-thymocyte globulin (ATG), clinical response to cyclosporine was seen in two cases. There was improvement of platelet count in one case and complete clinical response in another. Taken together, it is plausible that +6 defines a distinctive subtype of aplastic anaemia with mild dysplastic changes, poor response to steroids and ATG therapy, and a propensity for AML transformation.

Rare instances of +6 may be encountered in childhood acute mixed lineage leukaemia, lymphoblastic transformation of chronic myeloid leukaemia, and chronic myeloproliferative disorder.

Phenotype / cell stem origin Three out of four AML patients with +6 in one series showed AML-M1 morphology and expression of stem cell antigen CD34 on the leukaemic blasts, suggesting that +6 may be associated with a more primitive form of AML. Evolution A case of aplastic anaemia with +6 and no dysplasia showed transformation into AML at 15 months after initial diagnosis. Prognosis Trisomy 6 may define a distinctive subtype of aplastic anaemia with mild dysplastic changes, poor response to steroids and ATG therapy, and a propensity for AML transformation. More cases need to be collected to substantiate this contention.

 

Cytogenics  Complete karyotype showing 47,XY,+6. G-banding with trypsin/Giemsa. The patient is an 81-year old Chinese man who was admitted for myocardial infarction and was found to be anaemic. Physical examination was unremarkable. Blood counts showed: haemoglobin 8.6 g/dL, white cell count 3.2 X 109/L, and platelet count 174 X 109/L. Bone marrow morphology, cytochemistry and immunophenotyping results were consistent with a diagnosis of acute myeloid leukaemia. Chromosome analysis on bone marrow cells showed: 47,XY,+6[2]/46,XY[5].

Bibliography

Trisomy 6 associated with aplastic anemia. Geraedts JP, Haak HL. Hum Genet 1976; 35: 113-115. Medline 1002160   Correlation between prognosis and bone marrow chromosomal patterns in children with acute nonlymphocytic leukemia: similarities and differences compared to adults. Benedict WF, Lange M, Greene J, Derencsenyi A, Alfi OS. Blood 1979; 54: 818-823. Medline 289424   Chromosome aberrations and prognosis in preleukaemia. Panani A, Papayannis AG, Sioula E. Scand J Haematol 1980; 24: 97-100. Medline 6929565   Chromosomal alterations in acute leukemia patients studied with improved culture methods. Testa JR, Misawa S, Oguma N, Van Sloten K, Wiernik PH. Cancer Res 1985; 45: 430-434. Medline 3855285   Multiple chromosomally distinct cell populations in myelodysplastic syndromes and their possible significance in the evolution of the disease. Mecucci C, Rege-Cambrin G, Michaux JL, Tricot G, Van den Berghe H. Br J Haematol 1986; 64: 699-706. Medline 3801319   Clonal cytogenetic abnormalities in patients with otherwise typical aplastic anemia. Appelbaum FR, Barrall J, Storb R, Ramberg R, Doney K, Sale GE, Thomas ED. Exp Hematol 1987; 15: 1134-1139. Medline 3315724   Prognostic significance of chromosome analysis in de novo acute myeloid leukemia (AML). Weh HJ, Kuse R, Hoffmann R, Seeger D, Suciu S, Kabisch H, Ritter J, Hossfeld DK. Blut 1988; 56: 19-26. Medline 3422167   Trisomy 6: a recurring cytogenetic abnormality associated with marrow hypoplasia. Moormeier JA, Rubin CM, Le Beau MM, Vardiman JW, Larson RA, Winter JN. Blood 1991; 77: 1397-1398. Medline 2001462   Cytogenetic analysis of hematologic malignancies in Hong Kong. A study of 98 cases. Chan LC, Kwong YL, Liu HW, Chan TK, Todd D, Ching LM. Cancer Genet Cytogenet 1992; 62: 154-159. Medline 1394102   Trisomy 6 as the sole chromosome abnormality in myeloid disorders. Jonveaux P, Fenaux P, Berger R. Cancer Genet Cytogenet 1994; 74: 150-152. Medline 8019961   Primary, single, autosomal trisomies associated with haematological disorders. United Kingdom Cancer Cytogenetics Group (UKCCG). Leuk Res 1996; 16: 841-851. Medline 1405715   Trisomy 6 is the hallmark of a dysplastic clone in bone marrow aplasia. La Starza R, Matteucci C, Crescenzi B, Criel A, Selleslag D, Martelli MF, Van den Berghe H, Mecucci C. Cancer Genet Cytogenet 1998; 105: 55-59. Medline 9689931   Trisomy 6 as a primary karyotypic aberration in hematologic disorders. Mohamed AN, Varterasian ML, Dobin SM, McConnell TS, Wolman SR, Rankin C, Willman CL, Head DR, Slovak ML. Cancer Genet Cytogenet 1998; 106: 152-155. Medline 9797781   Trisomy 6 in a childhood acute mixed lineage leukemia. Onodera N, Nakahata T, Tanaka H, Ito R, Honda T. Acta Paediatr Jpn 1998; 40: 616-620. Medline 9893302   Trisomy 6 and double minute chromosomes in a case of chronic myelomonocytic leukemia. Sambani C, Trafalis DT,Vessalas G, Politis G, Peristeris P, Nakopoulou L, Giannopoulou J, Michaelidis C, Ayoutantis M, Pantelias GE. Cancer Genet Cytogenet 1998; 106: 180-181. Medline 9797788   Trisomy 6 acquired in lymphoid blast transformation of chronic myelocytic leukemia with t(9;22). Yilmaz Y, Klein R, Qumsiyeh MB. Cancer Genet Cytogenet 2003; 145: 86-87. Medline 12885470   A rapidly progressive chronic myeloproliferative disease with isolated trisomy 6. Wong KF. Cancer Genet Cytogenet 2004; 149: 176-177.

Medline 15036897

Trisomy 6

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