Ocular ochronosis in alkaptonuria patients carrying mutations in the homogentisate 1,2-dioxygenase gene

Abstract

Aims: To assess the involvement of the recently identified human homogentisate 1,2-dioxygenase gene (HGO) in alkaptonuria (AKU) in two unrelated patients with ochronosis of the conjunctiva, sclera, and cornea.

Methods: A mutation screen of the entire coding region of the HGO gene was performed using single stranded conformational analysis after polymerase chain reaction with oligonucleotide primers flanking all 14 exons of the HGO gene. Fragments showing aberrant mobility were directly sequenced.

Results: Two homozygous missense mutations, L25P and M368V, were identified, each of which leads to the replacement of a highly conserved amino acid in the HGO protein.

Conclusions: The authors describe a novel mutation, L25P, in the German population and bring to 18 the total number of known HGO mutations.

Figure 1

Ochronotic pigment in the conjunctiva, sclera, and peripheral cornea of 71 year old patient, H.

Figure 2

Mutation analysis of exon 2 of the human HGO gene. (A) SSCA revealed a homozygous mobility shift in patient L (L) compared with controls (C). (B) PCR sequencing detected a homozygous T to C transition at the second position of codon 25 changing a leucine residue to a proline (L25P).

Figure 3

(A) SSCA of exon 13 of the HGO gene showed a homozygous band shift in patient H (H). (C) = controls, (X) = unpublished heterozygous mutation. (B) Both patient H and her affected brother P (P) carry a homozygous A to G substitution changing codon 368 from methionine to valine (M368V).