Sequence analysis of the homogentisate 1,2 dioxygenase gene in a family affected by alkaptonuria (original) (raw)

1999, Journal of medical genetics

Sequence analysis of the homogentisate 1,2 dioxygenase gene in a family aVected by alkaptonuria EDITOR-Alkaptonuria (AKU) is a disorder of the catabolism of aromatic amino acids. A defect of homogentisate 1,2 dioxygenase (HGO) leads to an accumulation of homogentisic acid (HGA) and subsequently to deposition of polymerised HGA, a brown-black pigment, in connective tissue, primarily in cartilage. 1 2 This phenomenon is known as ochronosis. It results in debilitating arthropathy which typically becomes manifest in the fourth decade of life. Large amounts of HGA are excreted in the urine and cause its black discolouration upon oxidation. In 1891, homogentisic acid was first isolated by Wolkow and Baumann 3 from the urine of an AKU patient from a remote area of the Black Forest in south western Germany. In 1902, Garrod, aware of this biochemical finding, observed the autosomal recessive mode of inheritance of AKU and thereby showed for the first time that mendelian laws also apply to human genetics. 4 Garrod postulated that AKU results from an enzyme deficiency and introduced the concept of the "inborn error of metabolism". 5 Recently, the human gene encoding HGO was cloned by Fernádez-Cañón et al. 6 Two diVerent mutations of this gene were identified in two unrelated AKU aVected families. These mutations cosegregated with manifest disease and could be shown to abrogate enzymatic activity of HGO protein. 6 Homozygosity for these mutations, therefore, was the cause of AKU in the two families. Two additional mutations in the HGO gene were found to cosegregate with AKU in two Slovakian pedigrees. 7 One of these mutations caused a frameshift in an upstream exon and was thus likely to result in a loss of HGO activity. For an additional mutation, complete cosegregation with AKU was reported in an extensively studied Canarian family. 8 Various diVerent mutations of the HGO gene were found in 14 unrelated AKU patients. 9 We performed sequence analysis of the HGO gene in an AKU aVected family from the Black Forest. AKU with severe ochronosis including involvement of the sclerae was diagnosed at necropsy of a 71 year old farmer (fig 1, No 1). The diagnosis of AKU had not been established during the patient's lifetime. He died of recurrent myocardial infarction. Subsequently, the patient's family underwent physical examination. A sister (fig 1, No 2) and a first cousin (fig 1, No 3) were found to be aVected by the disease. These patients have been suVering from arthritic symptoms of AKU since the fourth decade of life and show the typical discolouration of the urine and the ochronotic pigmentation of the sclerae. However, the condition had until then been misdiagnosed as degenerative polyarthritis. A brother (fig 1, No 4) of patient 1 was healthy as were the three children (fig 1, Nos 5, 6, and 7) of patient 2. Anamnestically, a brother (fig 1, No 8) and a first cousin (fig 1, No 9), who died in 1988 and 1995, respectively, were reported to have suVered from debilitating early onset polyarthropathy and the typical ochronotic involvement of the sclerae. They were very probably affected by AKU. No characteristic AKU symptoms were reported