Can Ebru Bekircan-Kurt1, Arda Çetinkaya2, Rahsan Gocmen3, Can Koşukcu4, Figen Soylemezoglu5, Ethem Murat Arsava6, Asli Tuncer6, Sevim Erdem-Ozdamar6, Nurten A Akarsu2, Mehmet Akif Topcuoglu6. 1. Department of Neurology, Neuromuscular Diseases Research Laboratory, Hacettepe University, Medical Faculty, Sihhiye Ankara 06100, Turkey. Electronic address: canebru@yahoo.co.uk. 2. Department of Medical Genetics, Hacettepe University, Medical Faculty, Ankara, Turkey. 3. Department of Radiology, Hacettepe University, Medical Faculty, Ankara, Turkey. 4. Department of Bioinformatics, Hacettepe University, Graduate School of Health Sciences, Ankara, Turkey. 5. Department of Pathology, Hacettepe University, Medical Faculty, Ankara, Turkey. 6. Department of Neurology, Neuromuscular Diseases Research Laboratory, Hacettepe University, Medical Faculty, Sihhiye Ankara 06100, Turkey.
Abstract
OBJECTIVES: To identify the underlying genetic defect for a consanguineous family with an unusually high number of members affected by cerebral small vessel disease. MATERIALS AND METHODS: A total of 6 individuals, of whom 3 are severely affected, from the family were clinically and radiologically evaluated. SNP genotyping was performed in multiple members to demonstrate genome-wide runs-of-homozygosity. Coding variants in the most likely candidate gene, HTRA1 were explored by Sanger sequencing. Published HTRA1-related phenotypes were extensively reviewed to explore the effect of number of affected alleles on phenotypic expression. RESULTS: Genome-wide homozygosity mapping identified a 3.2 Mbp stretch on chromosome 10q26.3 where HTRA1 gene is located. HTRA1 sequencing revealed an evolutionarily conserved novel homozygous c.824C>T (p.Pro275Leu) mutation, affecting the serine protease domain of HtrA1. Early-onset of cognitive and motor deterioration in homozygotes are in consensus with CARASIL. However, there was a clear phenotypic variability between homozygotes which includes alopecia, a suggested hallmark of CARASIL. All heterozygotes, presenting as CADASIL type 2, had spinal disk degeneration and several neuroimaging findings, including leukoencephalopathy and microhemorrhage despite a lack of severe clinical presentation. CONCLUSION: Here, we clearly demonstrate that CARASIL and CADASIL type 2 are two clinical consequences of the same disorder with different severities thorough the evaluation of the largest collection of homozygotes and heterozygotes segregating in a family. Considering the semi-dominant inheritance of HTRA1-related phenotypes, genetic testing and clinical follow-up must be offered for all members of a family with HTRA1 mutations regardless of symptoms.
OBJECTIVES: To identify the underlying genetic defect for a consanguineous family with an unusually high number of members affected by cerebral small vessel disease. MATERIALS AND METHODS: A total of 6 individuals, of whom 3 are severely affected, from the family were clinically and radiologically evaluated. SNP genotyping was performed in multiple members to demonstrate genome-wide runs-of-homozygosity. Coding variants in the most likely candidate gene, HTRA1 were explored by Sanger sequencing. Published HTRA1-related phenotypes were extensively reviewed to explore the effect of number of affected alleles on phenotypic expression. RESULTS: Genome-wide homozygosity mapping identified a 3.2 Mbp stretch on chromosome 10q26.3 where HTRA1 gene is located. HTRA1 sequencing revealed an evolutionarily conserved novel homozygous c.824C>T (p.Pro275Leu) mutation, affecting the serine protease domain of HtrA1. Early-onset of cognitive and motor deterioration in homozygotes are in consensus with CARASIL. However, there was a clear phenotypic variability between homozygotes which includes alopecia, a suggested hallmark of CARASIL. All heterozygotes, presenting as CADASIL type 2, had spinal disk degeneration and several neuroimaging findings, including leukoencephalopathy and microhemorrhage despite a lack of severe clinical presentation. CONCLUSION: Here, we clearly demonstrate that CARASIL and CADASIL type 2 are two clinical consequences of the same disorder with different severities thorough the evaluation of the largest collection of homozygotes and heterozygotes segregating in a family. Considering the semi-dominant inheritance of HTRA1-related phenotypes, genetic testing and clinical follow-up must be offered for all members of a family with HTRA1 mutations regardless of symptoms.