Exome capture sequencing identifies a novel mutation in BBS4.
OBJECTIVE
Leber congenital amaurosis (LCA) is one of the most severe eye dystrophies characterized by severe vision loss at an early stage and accounts for approximately 5% of all retinal dystrophies. The purpose of this study was to identify a novel LCA disease allele or gene and to develop an approach combining genetic mapping with whole exome sequencing.


METHODS
Three patients from King Khaled Eye Specialist Hospital (KKESH205) underwent whole genome single nucleotide polymorphism genotyping, and a single candidate region was identified. Taking advantage of next-generation high-throughput DNA sequencing technologies, whole exome capture sequencing was performed on patient KKESH205#7. Sanger direct sequencing was used during the validation step. The zebrafish model was used to examine the function of the mutant allele.


RESULTS
A novel missense mutation in Bardet-Biedl syndrome 4 protein (BBS4) was identified in a consanguineous family from Saudi Arabia. This missense mutation in the fifth exon (c.253G>C;p.E85Q) of BBS4 is likely a disease-causing mutation as it segregates with the disease. The mutation is not found in the single nucleotide polymorphism (SNP) database, the 1000 Genomes Project, or matching normal controls. Functional analysis of this mutation in zebrafish indicates that the G253C allele is pathogenic. Coinjection of the G253C allele cannot rescue the mislocalization of rhodopsin in the retina when BBS4 is knocked down by morpholino injection. Immunofluorescence analysis in cell culture shows that this missense mutation in BBS4 does not cause obvious defects in protein expression or pericentriolar localization.


CONCLUSIONS
This mutation likely mainly reduces or abolishes BBS4 function in the retina. Further studies of this allele will provide important insights concerning the pleiotropic nature of BBS4 function.
Human Genome Sequencing Center, Baylor College of Medicine, Houston, TX, USA.
Hui
H
Wang
Xianfeng
X
Chen
Lynn
L
Dudinsky
Claire
C
Patenia
Yiyun
Y
Chen
Yumei
Y
Li
Yue
Y
Wei
Emad B
EB
Abboud
Ali A
AA
Al-Rajhi
Richard Alan
RA
Lewis
James R
JR
Lupski
Graeme
G
Mardon
Richard A
RA
Gibbs
Brian D
BD
Perkins
Rui
R
Chen
D000483:Alleles; D000818:Animals; D001483:Base Sequence; D002874:Chromosome Mapping; D003241:Consanguinity; D059472:Exome; D005091:Exons; D005260:Female; D005838:Genotype; D059014:High-Throughput Nucleotide Sequencing; D006801:Humans; D007223:Infant; D057130:Leber Congenital Amaurosis / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D008297:Male; D008869:Microtubule-Associated Proteins; D008969:Molecular Sequence Data; D020125:Mutation, Missense; D010375:Pedigree; D020641:Polymorphism, Single Nucleotide; D011506:Proteins / Q000235:genetics* / Q000378:metabolism; D012160:Retina / Q000378:metabolism* / Q000473:pathology; D012243:Rhodopsin / Q000378:metabolism; D012529:Saudi Arabia; D015027:Zebrafish
C429655:BBS4 protein, human; D008869:Microtubule-Associated Proteins; D011506:Proteins; D012243:Rhodopsin