Clinical and genetic investigation of a large Tunisian family with complete achromatopsia: identification of a new nonsense mutation in GNAT2 gene.
Complete achromatopsia is a rare autosomal recessive disease associated with CNGA3, CNGB3, GNAT2 and PDE6C mutations. This retinal disorder is characterized by complete loss of color discrimination due to the absence or alteration of the cones function. The purpose of the present study was the clinical and the genetic characterization of achromatopsia in a large consanguineous Tunisian family. Ophthalmic evaluation included a full clinical examination, color vision testing and electroretinography. Linkage analysis using microsatellite markers flanking CNGA3, CNGB3, GNAT2 and PDE6C genes was performed. Mutations were screened by direct sequencing. A total of 12 individuals were diagnosed with congenital complete achromatopsia. They are members of six nuclear consanguineous families belonging to the same large consanguineous family. Linkage analysis revealed linkage to GNAT2. Mutational screening of GNAT2 revealed three intronic variations c.119-69G>C, c.161+66A>T and c.875-31G>C that co-segregated with a novel mutation p.R313X. An identical GNAT2 haplotype segregating with this mutation was identified, indicating a founder mutation. All patients were homozygous for the p.R313X mutation. This is the first report of the clinical and genetic investigation of complete achromatopsia in North Africa and the largest family with recessive achromatopsia involving GNAT2; thus, providing a unique opportunity for genotype-phenotype correlation for this extremely rare condition.
Molecular Investigation of Genetic Orphan Diseases Research Unit UR04/SP03, Pasteur Institute, Tunis, Tunisia.
Farah
F
Ouechtati
Ahlem
A
Merdassi
Yosra
Y
Bouyacoub
Leila
L
Largueche
Kaouther
K
Derouiche
Houyem
H
Ouragini
Sonia
S
Nouira
Leila
L
Tiab
Karim
K
Baklouti
Ahmed
A
Rebai
Daniel F
DF
Schorderet
Francis L
FL
Munier
Leonidas
L
Zografos
Sonia
S
Abdelhak
Leila
L
El Matri
D000293:Adolescent; D000328:Adult; D002648:Child; D018389:Codon, Nonsense / Q000502:physiology; D003117:Color Vision Defects / Q000175:diagnosis* / Q000235:genetics* / Q000503:physiopathology; D004252:DNA Mutational Analysis; D005136:Eye Proteins / Q000235:genetics*; D005190:Family; D005260:Female; D056726:Genetic Association Studies; D006801:Humans; D008297:Male; D008875:Middle Aged; D010375:Pedigree; D020641:Polymorphism, Single Nucleotide / Q000502:physiology; D015293:Transducin / Q000235:genetics; D014416:Tunisia; D055815:Young Adult
D018389:Codon, Nonsense; D005136:Eye Proteins; D015293:Transducin