EPOS

European Paediatric Ophthalmological Society

Abstract Preview

Screening of NUB1 in Patients with Leber congenital amaurosis

Preising Markus, Sitorus Rita, Rosenberg Thomas, Kellner Ulrich, Lorenz Birgit
¹Dept. of Paed. Ophthalmology, Strabismology, and Ophthalmogenetics, University of Regensburg, Klinikum, Regensburg, Germany, ²National Eye Clinic for the Visually Impaired, Hellerup, Denmark, ³Eye Clinic, University Clinic Benjamin Franklin, Berlin, Germany

Purpose: To identify disease causing mutations in the NUB1 gene underlying Leber Congenital Amaurosis (LCA). NUB1 has been reported as an interaction protein of AIPL1 recently. We tested the hypothesis that mutations in NUB1 cause a LCA phenotype. A first focus was set on patients carrying missense mutations in the AIPL1 gene previously reported as non-pathogenic. Methods: Index cases with LCA (n=67) examined by the authors (n=50) and by collaborating local ophthalmologists (n=17) were screened for mutations in the AIPL1 and NUB1 genes by SSCP and direct sequencing. Results: 8 index cases were identified to carry missense mutations in the AIPL1 gene. Among these mutations the D90H polymorphism was identified in 5 of 16 alleles. The other mutations included R53W, H82Y, C89Y, C89R, V96I, and I206N. All of these were present in the single heterozygous state or with D90H as compound allele. The NUB1 gene was screened in these 8 index cases carrying AIPL1 missense mutations. In these patients we identified three polymorphisms. Two of these were frequent SNPs (A577A, Y280Y) useful for linkage studies. Using these SNPs we could exclude the NUB1 gene as disease causing gene in 3 familial index cases. No other disease causing mutations could be identified up to now in the patients carrying AIPL1 missense mutations. Conclusion: The D90H mutation of AIPL1 has been reported previously as a benign variant. Our results in a screen of 66 index cases revealed two independent families with this mutation possibly indicating some pathogeneity. However, control DNAs of 50 unaffected probands from the general population revealed 2 homozygous and 6 single heterozygous individuals. If at all D90H predisposes to LCA a mutation in a second gene has to be expected. Four further 4 AIPL1 mutations affected conserved residues in primates and were not found in the control DNAs. These mutations are localized in the vicinity of the D90 residue in a region of unknown protein function. We screened an AIPL1-interacting protein NUB1 which shares features of ubiquitin in 8 LCA patients carrying AIPL1 missense mutations of unknown pathogeneity. No NUB1 mutation could be found in these LCA patients so far. The current results do not support a digenic inheritance in LCA in our samples. A further set of LCA patients without mutations in AIPL1 is now under investigation for NUB1 mutations.