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Hereditary cystatin C amyloid angiopathy: identification of the disease-causing mutation and specific diagnosis by
M Abrahamson1, S Jonsdottir, I Olafsson
1Department of Clinical Chemistry, University of Lund, University Hospital, Sweden.
Insights
Hereditary cystatin C amyloid angiopathy (HCCAA) diagnosis is simplified using DNA amplification and AluI digestion. This method accurately identifies the T-to-A mutation causing HCCAA in young adults.
Area of Science:
- Genetics
- Neurology
- Molecular Biology
Background:
- Hereditary cystatin C amyloid angiopathy (HCCAA) is a severe, dominantly inherited neurological disorder.
- HCCAA presents with amyloidosis, dementia, and fatal cerebral hemorrhage in young adults.
- Accurate and rapid diagnosis is crucial for managing HCCAA.
Purpose of the Study:
- To develop a rapid and simple diagnostic method for HCCAA.
- To identify the specific genetic mutation responsible for HCCAA.
Main Methods:
- Oligonucleotide-directed enzymatic amplification of a 275-bp genomic DNA segment from the cystatin C gene (exon 2).
- Digestion of the amplified DNA product with the restriction enzyme AluI.
- Agarose gel electrophoresis to detect altered band patterns indicative of HCCAA.
- Nucleotide sequencing to confirm the mutation in affected individuals.
Main Results:
- The diagnostic procedure achieved 100% sensitivity and specificity for HCCAA.
- A distinct band pattern was observed in HCCAA patients due to the loss of an AluI recognition site.
- Nucleotide sequencing revealed a consistent single T-to-A substitution at codon 68 of the cystatin C gene in all tested HCCAA families.
Conclusions:
- A reliable molecular diagnostic test for HCCAA has been established.
- The identified T-to-A mutation is the causative genetic defect in HCCAA.
- This diagnostic method facilitates early and accurate identification of individuals with HCCAA.
Abstract:
Hereditary cystatin C amyloid angiopathy (HCCAA) is a dominantly inherited disease characterized by amyloidosis, dementia and fatal cerebral hemorrhage of young adults. A method for rapid and simple diagnosis of HCCAA is described. It is based upon oligonucleotide-directed enzymatic amplification of a 275-bp genomic DNA segment containing exon 2 of the cystatin C gene from a blood sample, followed by digestion of the amplification product with AluI. Loss of an AluI recognition site in the amplified DNA segment from HCCAA patients results in a deviating band-pattern at agarose gel electrophoresis, compared with that obtained from normal subjects or unaffected HCCAA family members. In a population of 9 patients with manifest HCCAA, 14 patients with other causes of brain hemorrhage and 16 healthy individuals, the diagnostic procedure displayed a sensitivity and specificity for HCCAA of 100%. Amplified DNA segments from 4 HCCAA patients of four different families were analyzed by nucleotide sequencing; the HCCAA-causing mutation in all families was found to be a single T----A substitution in the codon for amino acid residue 68 of cystatin C.