Mutation analysis and clinical implications of von Willebrand factor-cleaving protease deficiency.
BACKGROUND
The pentad of thrombocytopenia, hemolytic anemia, mild renal dysfunction, neurologic signs, and fever, classically characterizes the syndrome of thrombotic thrombocytopenic purpura (TTP). TTP usually occurs in adults as an acquired form but a congenital form in children has also been described. In the latter case, the initial presentation is often with neonatal jaundice and thrombocytopenia. The disorder may subsequently take a relapsing course. Deficiency of a recently identified novel metalloprotease, the von Willebrand factor (vWF)-cleaving protease, originating from mutations in the ADAMTS13 gene plays a major role in the development of TTP.


METHODS
Blood for DNA analysis was collected from six unrelated TTP families, consisting of nine patients from four different countries, and was screened for mutations in the ADAMTS13 gene. This gene spans 29 exons encompassing approximately 37 kb. Conventional techniques of DNA extraction, polymerase chain reaction (PCR), and direct cycle sequencing were used.


RESULTS
Eight novel ADAMTS13 mutations are presented. Half of the total number of mutant ADAMTS13 alleles are amino acid substitutions. The disease-causing mutations are spread over the gene. The pathogenicity of the individual mutations is based upon their predicted effect on the ADAMTS13 protein and segregation in family members. Although most of the patients (seven out of nine) had symptoms during the neonatal period, they were in a remarkably good condition. Only one of the nine patients had a decreased glomerular filtration rate (GFR) with proteinuria and hematuria. Another patient had epileptic seizures.


CONCLUSIONS
We confirm that deficiency of ADAMTS13 is a molecular mechanism responsible for familial TTP. An early diagnosis allows prophylactic treatment with fresh plasma infusions.
Assink
Karin
K
Department of Pediatric Nephrology, University Medical Centre Nijmegen, Nijmegen, The Netherlands.
Schiphorst
Rikke
R
Allford
Sarah
S
Karpman
Diana
D
Etzioni
Amos
A
Brichard
Bénédicte
B
van de Kar
Nicole
N
Monnens
Leo
L
van den Heuvel
Lambertus
L
D051722:ADAM Proteins; D000071120:ADAMTS13 Protein; D019943:Amino Acid Substitution / Q000235:genetics; D002648:Child; D002675:Child, Preschool; D004252:DNA Mutational Analysis; D005260:Female; D006579:Heterozygote; D006720:Homozygote; D006801:Humans; D008297:Male; D008666:Metalloendopeptidases / Q000235:genetics*; D017354:Point Mutation; D011697:Purpura, Thrombotic Thrombocytopenic / Q000235:genetics*
D051722:ADAM Proteins; D008666:Metalloendopeptidases; D000071120:ADAMTS13 Protein; C099604:ADAMTS13 protein, human