Concurrent but apparently unrelated structural rearrangements of the band p13 of both chromosome 16 homologues in a case of renal angiomyolipoma. S. Wei¹, C. Abbud-Mendez², M.W. Lee², A. Adeyinka¹. 1) Dept Medical Genetics, Henry Ford Health System, Detroit, MI; 2) Dept of Pathology, Henry Ford Health System, Detroit, MI.
   Angiomyolipoma is a benign neoplasm arising from the mesenchymal tissues of the kidney and exhibiting a collection of blood vessels, smooth muscle, and mature adipose tissue. It is the most common mesenchymal tumor of the kidney and accounts for 0.7-2% of all kidney tumors. About 80% of renal angiomyolipoma are sporadic and are not associated with Tuberous Sclerosis Complex (TSC), whereas 20% are associated with tuberous sclerosis. TSC-associated angiomyolipomas are often multiple and bilateral, but histologically indistinguishable from sporadic renal angiomyolipoma. Clonal chromosome aberrations have been reported in 7 cases of sporadic renal angiomyolipoma including trisomy 7 as a sole abnormality in 3 tumors, trisomy 8 as a sole abnormality in one case, monosomy 8 with deletions in 11q23 and Xq26 in one tumor, a t(7;12) in one tumor and a complex rearrangement involving chromosomes 12 and 21 in one tumor. Loss of heterozygosity (LOH) in the chromosomal region for the TSC2 gene (16p13) has been documented in up to 60% of TSC-associated angiomyolipomas, whereas only few cases of sporadic angiomyolipoma have had LOH of 16p13. We report the cytogenetic findings in a renal angiomyolipoma from a 47-year-old woman without clinical history of tuberous sclerosis. Metaphase cells from primary cultures of the renal mass were 46,XX,der(7)t(7;16)(q11.2;p13.3),der(16)t(7;16)(q11.2;p13.3)t(16;17)(q13;q22),inv(16)(p13q22),add(17)(q11.2). Both chromosome 16 homologues had structural rearrangement of band p13 the chromosomal location of the TSC2 tumor suppressor gene. Since two events are required to inactivate both copies of a tumor suppressor gene, the present findings suggest that concurrent structural changes involving both chromosomal bands 16p13 may be a mechanism of tumorigenesis in sporadic renal angiomyolipoma.