title: Molecular diagnosis of distal renal tubular acidosis in Tunisian patients: proposed algorithm for Northern Africa populations for the ATP6V1B1, ATP6V0A4 and SCL4A1 genes.
abstract: BACKGROUND
  Primary distal renal tubular acidosis (dRTA) caused by mutations in the genes that codify for the H + -ATPase pump subunits is a heterogeneous disease with a poor phenotype-genotype correlation. Up to now, large cohorts of dRTA Tunisian patients have not been analyzed, and molecular defects may differ from those described in other ethnicities. We aim to identify molecular defects present in the ATP6V1B1, ATP6V0A4 and SLC4A1 genes in a Tunisian cohort, according to the following algorithm: first, ATP6V1B1 gene analysis in dRTA patients with sensorineural hearing loss (SNHL) or unknown hearing status. Afterwards, ATP6V0A4 gene study in dRTA patients with normal hearing, and in those without any structural mutation in the ATP6V1B1 gene despite presenting SNHL. Finally, analysis of the SLC4A1 gene in those patients with a negative result for the previous studies.
  
  
  METHODS
  25 children (19 boys) with dRTA from 20 families of Tunisian origin were studied. DNAs were extracted by the standard phenol/chloroform method. Molecular analysis was performed by PCR amplification and direct sequencing.
  
  
  RESULTS
  In the index cases, ATP6V1B1 gene screening resulted in a mutation detection rate of 81.25%, which increased up to 95% after ATP6V0A4 gene analysis. Three ATP6V1B1 mutations were observed: one frameshift mutation (c.1155dupC; p.Ile386fs), in exon 12; a G to C single nucleotide substitution, on the acceptor splicing site (c.175-1G > C; p.?) in intron 2, and one novel missense mutation (c.1102G > A; p.Glu368Lys), in exon 11. We also report four mutations in the ATP6V0A4 gene: one single nucleotide deletion in exon 13 (c.1221delG; p.Met408Cysfs*10); the nonsense c.16C > T; p.Arg6*, in exon 3; and the missense changes c.1739 T > C; p.Met580Thr, in exon 17 and c.2035G > T; p.Asp679Tyr, in exon 19.
  
  
  CONCLUSIONS
  Molecular diagnosis of ATP6V1B1 and ATP6V0A4 genes was performed in a large Tunisian cohort with dRTA. We identified three different ATP6V1B1 and four different ATP6V0A4 mutations in 25 Tunisian children. One of them, c.1102G > A; p.Glu368Lys in the ATP6V1B1 gene, had not previously been described. Among deaf since childhood patients, 75% had the ATP6V1B1 gene c.1155dupC mutation in homozygosis. Based on the results, we propose a new diagnostic strategy to facilitate the genetic testing in North Africans with dRTA and SNHL.
authors.affiliation: Department of Pediatrics, School of Medicine and Odontology, UPV/EHU, Bizkaia, Spain. gariceta@vhebron.net.
authors.forename: Donia
authors.initials: D
authors.lastname: Elhayek
authors.forename: Gustavo
authors.initials: G
authors.lastname: Perez de Nanclares
authors.forename: Slaheddine
authors.initials: S
authors.lastname: Chouchane
authors.forename: Saber
authors.initials: S
authors.lastname: Hamami
authors.forename: Adnène
authors.initials: A
authors.lastname: Mlika
authors.forename: Monia
authors.initials: M
authors.lastname: Troudi
authors.forename: Nadia
authors.initials: N
authors.lastname: Leban
authors.forename: Wafa
authors.initials: W
authors.lastname: Ben Romdane
authors.forename: Mohamed Neji
authors.initials: MN
authors.lastname: Gueddiche
authors.forename: Féthi
authors.initials: F
authors.lastname: El Amri
authors.forename: Samir
authors.initials: S
authors.lastname: Mrabet
authors.forename: Jemni
authors.initials: J
authors.lastname: Ben Chibani
authors.forename: Luis
authors.initials: L
authors.lastname: Castaño
authors.forename: Amel
authors.initials: A
authors.lastname: Haj Khelil
authors.forename: Gema
authors.initials: G
authors.lastname: Ariceta
mesh_terms: D000141:Acidosis, Renal Tubular / Q000175:diagnosis* / Q000235:genetics*; D000465:Algorithms; D001457:Anion Exchange Protein 1, Erythrocyte / Q000235:genetics*; D044383:Black People / Q000235:genetics*; D002675:Child, Preschool; D015331:Cohort Studies; D005091:Exons; D005260:Female; D016368:Frameshift Mutation; D017353:Gene Deletion; D006319:Hearing Loss, Sensorineural / Q000235:genetics / Q000473:pathology; D006720:Homozygote; D006801:Humans; D007223:Infant; D008297:Male; D020125:Mutation, Missense; D014416:Tunisia; D025262:Vacuolar Proton-Translocating ATPases / Q000235:genetics*
chemical_list: C509766:ATP6V1B1 protein, human; D001457:Anion Exchange Protein 1, Erythrocyte; C454201:SLC4A1 protein, human; C490181:ATP6V0A4 protein, human; D025262:Vacuolar Proton-Translocating ATPases