Truncating mutations in the Wilson disease gene ATP7B are associated with very low serum ceruloplasmin oxidase activity and an early onset of Wilson disease.
BACKGROUND
Mutations in the gene ATP7B cause Wilson disease, a copper storage disorder with a high phenotypic and genetic heterogeneity. We aimed to evaluate whether 'severe' protein-truncating ATP7B mutations (SMs) are associated with low serum ceruloplasmin oxidase activities and an early age of onset when compared to missense mutations (MMs).


METHODS
The clinical phenotype of 59 genetically confirmed WD patients was analyzed retrospectively. Serum ceruloplasmin was measured by its oxidase activity with o-dianisidine dihydrochloride as substrate and immunologically.


RESULTS
Thirty-nine patients had two MMs, 15 had the genotype SM/MM, and 5 patients had two SMs on their ATP7B alleles. Enzymatic and immunologic serum ceruloplasmin levels differed significantly between the three groups (P < 0.001 and P < 0.01, respectively). The lowest levels were measured in patients with two SMs (0.0 U/L; IQR, 0.0-0.0 U/L and 0.02 g/L; IQR, 0.01-0.02 g/L, respectively) and the highest in patients with two MMs (17.8 U/L; IQR, 5.8-35.1 U/L and 0.11 g/L; IQR,0.10-0.17 g/L, respectively). The age of onset was also significantly different between the three patient groups (P < 0.05), with SM/SM patients showing the earliest onset (13 years; IQR, 9-13 years) and patients with two MMs showing the latest onset (22 years; IQR, 14-27 years). By ROC curve analysis a ceruloplasmin oxidase level <or= 5 U/L can predict the presence of at least one SM with a sensitivity of 80% and a specificity of 79.5%.


CONCLUSIONS
In our German study cohort truncating ATP7B mutations were associated with lower ceruloplasmin serum oxidase levels and an earlier age of onset when compared to MMs. Measurement of serum ceruloplasmin oxidase might help to predict presence of truncating ATP7B mutations and might facilitate the mutation analysis.
Merle
Uta
U
Department of Gastroenterology and Hepatology, University Hospital, Heidelberg, Germany. uta_merle@med.uni-heidelberg.de
Weiss
Karl Heinz
KH
Eisenbach
Christoph
C
Tuma
Sabine
S
Ferenci
Peter
P
Stremmel
Wolfgang
W
D000251:Adenosine Triphosphatases / Q000235:genetics*; D000293:Adolescent; D000328:Adult; D017668:Age of Onset; D027682:Cation Transport Proteins / Q000235:genetics*; D002570:Ceruloplasmin / Q000378:metabolism*; D002648:Child; D015331:Cohort Studies; D000073840:Copper-Transporting ATPases; D005260:Female; D005838:Genotype; D006527:Hepatolenticular Degeneration / Q000097:blood / Q000201:enzymology* / Q000453:epidemiology / Q000235:genetics*; D006801:Humans; D008297:Male; D009154:Mutation; D020125:Mutation, Missense; D012372:ROC Curve; D055815:Young Adult
D027682:Cation Transport Proteins; D002570:Ceruloplasmin; D000251:Adenosine Triphosphatases; C000612464:ATP7B protein, human; D000073840:Copper-Transporting ATPases