Abstract| Volume 252, SUPPLEMENT 1, S13, April 2021

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38. A rare constitutional 13q deletion associated with retinoblastoma and chronic lymphocytic leukemia

      The 13q deletion syndrome is a rare congenital disorder characterized by a wide phenotypic spectrum depending on the size and location of the deletion, with clinical features spanning intellectual disability, craniofacial dysmorphism, congenital malformations, and retinoblastoma (Mitter et al., 2011). In the somatic setting, deletion of 13q14 is the most common cytogenetic abnormality in chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL), and is associated with a favorable outcome when present as the sole cytogenetic abnormality (Van Dyke et al., 2010). To date, published reports and review of the literature have not associated constitutional 13q deletions to an increased risk of CLL/SLL. Here, we describe the molecular and cytogenetic analysis of a 47-year-old male referred to our laboratory for CLL genetic analysis. By fluorescence in situ hybridization (FISH), peripheral blood nuclei exhibited a homozygous 13q14 deletion in ∼63% of nuclei, and a heterozygous deletion in the remaining ∼37% of nuclei. FISH also identified heterozygous loss of the RB1 gene region in ∼97% of nuclei, consistent with the patient's history of retinoblastoma. Conventional chromosome analysis identified a large del(13)(q14.1q21.2), and chromosome microarray (CMA) mapped the deletion to 13:43,773,101-69,897,491 (26.1Mb, hg19) in a perfect heterozygous state. In essential agreement with the FISH results, CMA also identified a homozygous 796Kb deletion including MIR16-1, MIR15A, and DLEU1/2 in ∼50% of cells; this homozygous deletion likely represents the CLL cell population. To our knowledge this is the first case of a constitutional 13q deletion associated with adult CLL. Given that monoallelic deletions of RB1 constitute ∼6% of RB1’s mutational spectrum (Albretch et al., 2005; Castéra et al., 2013), a better understanding of this patient may help explore the risk for adult-onset CLL in those individuals with an infantile history of retinoblastoma who carry an RB1 deletion rather than a point mutation.
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