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Optic atrophy type 1 (OPA1, MIM 165500) is a dominantly inherited optic neuropathy occurring in 1 in 50,000 individuals 1 , 2 , 3 that features progressive loss in visual acuity leading, in many cases, to legal blindness 4 , 5 , 6 , 7 , 8 . Phenotypic variations 5 and loss of retinal ganglion cells 9 , 10 , as found in Leber hereditary optic neuropathy (LHON), have suggested possible mitochondrial impairment 11 , 12 . The OPA1 gene has been localized to 3q28–q29 (refs 13 – 19 ). We describe here a nuclear gene, OPA1 , that maps within the candidate region and encodes a dynamin-related protein localized to mitochondria. We found four different OPA1 mutations, including frameshift and missense mutations, to segregate with the disease, demonstrating a role for mitochondria in retinal ganglion cell pathophysiology.

Ewing's sarcoma, 1 the second most common malignant bone tumor of children and young adults, is an aggressive osteolytic tumor with a marked propensity for dissemination. Accurate and rapid diagnosis is essential for clinical management, but classification of the neoplasm can be difficult because the microscopical appearance of the tumor is not specific. Ewing's sarcoma belongs to the heterogeneous group of small-round-cell tumors 2 . The tumor cells are uniformly bland and undifferentiated, with a surprisingly low mitotic index given the rapid growth observed clinically. The presence of large amounts of intracellular glycogen is not a specific finding, since up to 35 . . .

To the Editor: We performed a cytogenetic analysis in four cases of Ewing's tumor. All metaphases were obtained after two-day cultures of fresh tumor cells. RHG- and THA-banded chromosomes 1 , 2 were analyzed, and the structural rearrangements were classified according to the international nomenclature. 3 In all four cases clones with abnormalities were observed, and no cells with normal karyotype could be found. In all the cells, we observed reciprocal translocations involving band ql2 of chromosome 22 (Fig. 1): in Case 1, t(2;22;ll)(p22;ql2;?); in Case 2, t(9;22;20)(q34;ql2;pl2); in Case 3, t(l1;22)(q24;ql2); and in Case 4, t(ll;22)(q24;ql2) and t(l;22)(p21;ql2). Additional chromosomal abnormalities were observed . . . No extract is available for articles shorter than 400 words.