Feline congenital erythropoietic porphyria: two homozygous UROS missense mutations cause the enzyme deficiency and porphyrin accumulation

• Published in: Molecular medicine (Cambridge, Mass.) Vol. 16; no. 9-10; pp. 381 - 388
• Main Authors: Clavero, Sonia, Bishop, David F, Giger, Urs, Haskins, Mark E, Desnick, Robert J
• Format: Journal Article
• Language: English
• Published: England ScholarOne 01.09.2010
• Subjects: Animals; Cat Diseases - blood; Cat Diseases - enzymology; Cat Diseases - genetics; Cat Diseases - urine; Cats; Erythrocytes - metabolism; Homozygote; Male; Models, Molecular; Molecular Sequence Data; Mutant Proteins - chemistry; Mutant Proteins - genetics; Mutant Proteins - metabolism; Mutation, Missense - genetics; Porphyria, Erythropoietic - blood; Porphyria, Erythropoietic - enzymology; Porphyria, Erythropoietic - urine; Porphyria, Erythropoietic - veterinary; Porphyrins - blood; Porphyrins - metabolism; Porphyrins - urine; Uroporphyrinogen III Synthetase - chemistry; Uroporphyrinogen III Synthetase - genetics; Uroporphyrinogen III Synthetase - metabolism
• ISSN: 1076-1551; 1528-3658
• DOI: 10.2119/molmed.2010.00038

The first feline model of human congenital erythropoietic porphyria (CEP) due to deficient uroporphyrinogen III synthase (URO-synthase) activity was identified by its characteristic clinical phenotype, and confirmed by biochemical and molecular genetic studies. The proband, an adult domestic shorthair cat, had dark-red urine and brownish discolored teeth with red fluorescence under ultraviolet light. Biochemical studies demonstrated markedly increased uroporphyrinogen I in urine and plasma (2,650- and 10,700-fold greater than wild type, respectively), whereas urinary 5-aminolevulinic acid and porphobilinogen were lower than normal. Erythrocytic URO-synthase activity was <1% of mean wild-type activity, confirming the diagnosis and distinguishing it from feline phenocopies having acute intermittent porphyria. Sequencing of the affected cat's UROS gene revealed two missense mutations, c.140C>T (p.S47F) in exon 3 and c.331G>A (p.G111S) in exon 6, both of which were homozygous, presumably owing to parental consanguinity. Neither was present in 100 normal cat alleles. Prokaryotic expression and thermostability studies of the purified monomeric wild-type, p.S47F, p.G111S, and p.S47F/G111S enzymes showed that the p.S47F enzyme had 100% of wild-type specific activity but ~50% decreased thermostability, whereas the p.G111S and p.S47F/G111S enzymes had about 60% and 20% of wild-type specific activity, respectively, and both were markedly thermolabile. Molecular modeling results indicated that the less active/less stable p.G111S enzyme was further functionally impaired by a structural interaction induced by the presence of the S47F substitution. Thus, the synergistic interaction of two rare amino acid substitutions in the URO-synthase polypeptide caused the feline model of human CEP.