Mutant cDNAs coding for dominant-negative forms of the fibroblast growth factor receptors 1 (FGFR-I) and 2 (FGFR-2) that lack tyrosine kinase activity were ligated to a 2.2 kb DNA fragment containing the bovine rhodopsin promoter and used to generate transgenic mice. Six independent lines were generated with the FGFR-1 construct, and five were generated with the FGFR-2 construct. Five of the six FGFR-1 mutant lines and all five FGFR-2 mutant lines showed transgene expression in the retina by reverse transcription-PCR.By both in situ hybridization and immunohistochemistry, mutant FGFRs were found to be expressed specifically in photoreceptors of transgenepositive FGFR-1 and FGFR-2 mice. Lines expressing the FGFR-2 mutant showed progressive photoreceptor degeneration; the retinas showed minimal or no abnormalities at 1 month, but by 2 months they showed focal areas of thinning of the outer nuclear layer and disruption of photoreceptors. By 2-4 months, areas of complete loss of photoreceptors were seen. These abnormalities were not seen in control littermates not expressing the transgene. Mice from two FGFR-1 mutant lines showed focal areas of thinning of the outer nuclear layer and numerous photoreceptors with fragmented chromatin, whereas the other FGFR-1 lines showed minimal or no abnormalities. These data indicate that perturbation of FGF signaling in photoreceptors is associated with progressive photoreceptor degeneration, suggesting that one or more of the FGFs may act as a survival factor for photoreceptor cells.

A 5-yr-old girl with unilateral retinoblastoma was found to have del(13)(q14.1q14.3). Her 16-month-old sister and 35-year-old mother, with retinal colobomata but without retinoblastoma, have the same deletion. Esterase D studies indicate reduced gene dose at this locus in the 3 females, consistent with a deletion of band 13q14. These patients are of apparently normal intelligence but have a mildly "coarse" facial appearance, a broad nasal bridge, upturned nares, and a long upper lip with thin upper lip vermillion similar to the phenotype suggested by Motegi et al [1983a] for patients with this deletion. Review of the literature documents 2 other patients with deletions of band 13q14 but without retinoblastoma, indicating that retinoblastoma is not a necessary consequence of this deletion. Of the 12 reported patients with deletions limited to band 13q14, seven had normal intelligence and five were macrocephalic. Insufficient clinical information is provided to draw conclusions about phenotype. The family which we describe and those reviewed by Motegi et al suggest that there may be a characteristic appearance in patients with this deletion.