Study On The Correlation Of Genotype And Clinical Phenotype In Leber Congenital Amaurosis

Purposes To identify the disease-causing genes and mutations of Leber congenital amaurosis(LCA) and early severe retinitis pigmentosa(ESRP), and to study the correlation of genotype and phenotype.Methods Patients diagnosed as LCA/ESRP in our outpatient during2003to2012were collected. Clinical features and genetic analysis were studied.①Clinical study Medical history and family history were recorded, and patients had ophthalmic examinations(including vision acuity, eye position and movement, pupillary light reflex, anterior segment and fundus examination), optometry, fundus photograph, electroretinogram(ERG) and optical coherence tomography(OCT) examination. When analyzing OCT, we used Calliper function to measure the fovea thickness manually, and read the corrected retina volume(diameter in3mm) in the post pole. Moreover, the retina structure, morphology, IS/OS and RPE signal were recorded at the same time.②Genetic study Venous blood(5-8ml) from patients were collected, and healthy volunteers were also collected. Genomic DNA was isolated from peripheral leukocytes using classic phenol-chloroform method. All coding exons, including intron-exon boundaries, of the AIPL1, GUCY2D, RDH12, LRAT, RPE65, CRB1and CRX genes were amplified by polymerase chain reaction(PCR), and the amplicons were sequenced directly. If mutations were found, single nucleotide polymorphism(SNP) analysis was performed in order to exclude polymorphisms. Consequently, by reading the published papers, we determined whether the mutations had been reported. If the mutation was novel, it is needed to amplify the mutation exon or intron, and sequence it in at least100normal subjects(200chromosomes) without relationship, in order to exclude the unknown population polymorphisms.Results109probands(57men and52women) were collected. The age at examination ranged from6months to39years, with a median age of10years.81patients were LCA and28patients were ESRP.108cases were bilateral and1case of ESRP was monocular.4cases were born from consanguineous marriage.24families had more than one patient, and the dominant inherence accounts for1.8%.95patients had vision examination,69patients had optometry,59patients had ERG and89patients had OCT examination. The disease-causing genes of35patients were identified, accounting for32.1%. There were3cases of AIPL1(2.8%),6cases of GUCY2D(5.5%),10cases of RDH12(9.2%), no case of LRAT,4cases of RPE65(3.7%),10cases of CRB1(9.2%) and2cases of CRX(1.8%). The clinical features of each genotype were as follows:AIPL1related LCA/ESRP had early onset with progressive degeneration. Macula usually showed gold foil reflection accompanied with retinal pepper salt or bone spicule pigmentation. OCT showed a flat and enlarged fovea with reduced retinal thickness and abnormal retinal lamination. IS/OS layer disappeared completely. The average fovea thickness was41.8±12.32μm, and retina volume(diameter in3mm) was1.43±0.13mm3. GUCY2D related LCA/ESRP had early onset with relatively stable condition. The patients had a normal appearing fundus. OCT showed a relatively normal morphology and laminated structure, usually with reduced retinal thickness or weak IS/OS signal. The average fovea thickness was119.00±45.18μm, and retina volume(diameter in3mm) was1.47mm3. RDH12related LCA/ESRP had childhood onset with progressive degeneration. The vision was relatively conserved at early age. The patients often had a petal like macular defect with dense bone spicule pigmentation. OCT showed a huge depressed deformation without normal retinal structure. Sometimes, OCT showed a flat and enlarged fovea with reduced retinal thickness and abnormal retinal lamination. IS/OS layer disappeared completely. The average fovea thickness was73.94±30.44μm, and retina volume (diameter in3mm) was1.44±0.26mm3. CRB1related LCA/ESRP had early onset with stable condition, usually accompanied with high hypermetropia. The fundus showed macular atrophy, even macular defect-like lesion, usually with round or copper cash pigmentation. OCT showed deep and enlarged fovea with reduced central fovea, however, parafoveal thickness usually increased. The retina often lack normal retinal structure and IS/OS signal. The average fovea thickness was50.64±29.50μm, and retina volume (diameter in3mm) was2.19±0.46mm3.CRX related LCA/ESRP had early onset with progressive degeneration. The patients often have a macular atrophy with different types of pigmentation. OCT showed a flat and enlarged fovea with reduced retinal thickness and abnormal retinal lamination. IS/OS signal disappeared completely. A patient's fovea thickness was119μm, and retina volume(diameter in3mm) was1.46mm3.Conclusions Each genotype of LCA/ESRP has its certain phenotype. The relationship between genotype and phenotype is obvious, especially the fundus and OCT manifestation. However, even similar clinical manifestation can be caused by different genes. On the other hand, because of the different mutations, environment influence and other factors, even the same disease-causing gene can lead to different phenotypes, making it complicated and easy to be misdiagnosed.