Abstract
Purpose: :
Leber Congenital Amaurosis (LCA) is the most severe inherited retinopathy with the earliest age of onset. Individuals affected with LCA are diagnosed at birth or in the first few months of life with severely impaired vision or blindness, nystagmus and abnormal or extinguished ERG. Non syndromic LCA has been associated with mutations in eight genes: AIPL1 (17p13.1), CRB1 (1q31–q32.2), CRX (19q13.3), GUCY2D (17p13.3), MERTK (2q14.1), LRAT (4q31), RPE65 (1p31) and RPGRIP1 (14q11). These genes are involved in different physiologic pathways in the retina.
Methods: :
We report a mutational analysis of all eight genes in 239 unrelated families. Mutational analysis was performed in 38 families diagnosed with LCA, 87 with early onset Retinitis Pigmentosa and 114 not–early onset Retinitis Pigmentosa. Samples were studied with a microarray (Asperbio) followed by a family study and direct sequencing in the laboratory.
Results: :
The respective frequencies of mutant alleles are: At the LCA group 26,3% (20/76), consisting of 38 patients, 12 are mutated patients: 1 carried an homozygous mutation, 4 are compound heterozygotes, 4 are single heterozygotes, and 3 are digenic or possible triallelic. For early–onset ARRP 12,1% (21/174), 87 families, with 18 mutated patients: 1 carried an homozygous mutation, 15 are single heterozygotes and 2 are digenic or possible triallelic. For ARRP not–early onset 9,6% (22/228), 114 families, with 19 mutated patients: 2 carried an homozygous mutation, 16 are single heterozygotes, and 1 is digenic or possible triallelic. At the digenic or triallelic cases we have continued the study in the rest of the family in order to describe the cosegregation of the mutations. Four families were available for detailed clinical and genetic analysis. CRB1 is the most mutated gene in Spanish affected families.
Conclusions: :
1. Using LCA microarray should be the first step in the molecular diagnosis when the clinical diagnosis indicates that is an LCA or early–onset ARRP case. 2. There is a gradient in mutation frequencies with respect to onset and severity of retinal disease, so correct classification of families is fundamental.
3. The relative percentage of mutations found with the microarray suggests that more LCA–associated genes remain to be discovered.
Keywords: gene microarray • gene modifiers • retina