OBJECTIVETo explore the incidence of chromosome 1 abnormality in myelodysplastic syndrome（MDS）to couple its association with clinical presentation and prognosis.

METHODSR- band karyotype analyses were performed in 672 cases of MDS between 2010 and 2013. Clinical data of those with abnormal chromosome l were collected and then analyzed factors affecting the prognosis.

RESULTSOf 672 cases of patients with MDS, chromosome 1 aberration［der（1）, dup（1）, －1 were most frequent］ were found in 41（6.1%）cases. 1q trisomy was found in 18/41（43.9%）cases, and the most common patterns were duplication of the long arm as well as unbalanced translocation with other chromosomes. Of 41 patients with chromosomal 1 abnormality, 32 cases were accompanied with other chromosomal aberration, usually involving 3 or more abnormal chromosomal karyotypes, e.g., chromosome 8, 7 abnormalities. According to IPSS-R scoring system, 19 patients were diagnosed with very high risk, 10 patients high risk, 10 patients intermediate risk and 2 patients low risk MDS. 9 patients transformed into acute leukemia with median transforming time of 7.18（0.56-54.28）months. Median survival of 36 cases after 2010 was 17.48（95% CI 14.38-20.58）months. There were significant differences on median survival between RAEB and non-RAEB groups（χ²=10.398, P=0.001）, and between with more than 3 chromosome abnormalities and with less than 3 groups（χ²=3.939, P=0.047）. RAEB was identified as an independent risk factor for the prognosis of MDS with chromosome 1 abnormality.

CONCLUSIONChromosome 1 aberration was not rare in MDS. 1q trisomy was the most common abnormal karyotype in China, which often accompanied with other chromosomal abnormalities. The prognosis of MDS patients with chromosome 1 abnormality was poor, especially worse in those diagnosed with RAEB-1, RAEB-2 and with more than 3 chromosome abnormality. For patients whose percentage of bone marrow blasts less than 5%, the prognosis of patients with 1q trisomy was better than those without 1q trisomy. RAEB was identified as an independent risk factor for the prognosis of MDS with chromosome 1 abnormality.