ABSTRACT
BACKGROUND/AIMS: Dent disease is an X-linked renal proximal tubulopathy associated with mutations in CLCN5 (Dent 1) or OCRL1 (Dent 2). OCRL1 mutations also cause the oculocerebrorenal syndrome of Lowe. METHODS: Dent patients with normal sequence for CLCN5 were sequenced for mutations in OCRL1. By analyzing these and all other OCRL1 mutations reported, a model relating OCRL1 mutations to the resulting disease (Dent 2 or Lowe's) was developed. RESULTS: Six boys with Dent disease had novel OCRL1 mutations: two missense (R301H, G304E) and four mutations predicted to produce premature termination codons (L56DfsX1, S149X, P161PfsX3, and M170IfsX1). These include one of the original patients reported by Dent and Friedman. Slit lamp examinations revealed early cataracts in only one boy with normal vision. None of these Dent 2 patients had metabolic acidosis; 3 had mild mental retardation. Analysis of all known OCRL1 mutations show that Dent 2 mutations fall into two classes that do not overlap with Lowe mutations. Bioinformatics analyses identified expressed OCRL1 splice variants that help explain the variability of those clinical features that distinguish Dent disease from Lowe syndrome. CONCLUSIONS: OCRL1 mutations can cause the renal phenotype of Dent disease, without acidosis or the dramatic eye abnormalities typical of Lowe syndrome. We propose a model to explain the phenotypic variability between Dent 2 and Lowe's based on distinctly different classes of mutations in OCRL1 producing splice variants.
Subject(s)
Mutation , Oculocerebrorenal Syndrome/genetics , Phosphoric Monoester Hydrolases/genetics , Renal Tubular Transport, Inborn Errors/genetics , Child , Child, Preschool , Chloride Channels/genetics , Codon, Nonsense , Computational Biology , DNA Mutational Analysis , Genetic Predisposition to Disease , Humans , Infant , Male , Models, Genetic , Mutation, Missense , Oculocerebrorenal Syndrome/diagnosis , Oculocerebrorenal Syndrome/metabolism , Phenotype , Phosphoric Monoester Hydrolases/metabolism , Protein Isoforms , Renal Tubular Transport, Inborn Errors/diagnosis , Renal Tubular Transport, Inborn Errors/metabolismABSTRACT
Mutations of the AE1 (SLC4A1, Anion-Exchanger 1) gene that codes for band 3, the renal and red cell anion exchanger, are responsible for many cases of familial distal renal tubular acidosis (dRTA). In Southeast Asia this disease is usually recessive, caused either by homozygosity of a single AE1 mutation or by compound heterozygosity of two different AE1 mutations. We describe two unrelated boys in Sarawak with dRTA associated with compound heterozygosity of AE1 mutations. Both had Southeast Asian ovalocytosis (SAO), a morphological abnormality of red cells caused by a deletion of band 3 residues 400-408. In addition, one boy had a DNA sequence abnormality of band 3 residue (G701D), which has been reported from elsewhere in Southeast Asia. The other boy had the novel sequence abnormality of band 3 (Q759H) and profound hemolytic anemia.
