Mutations in KRIT1 in familial cerebral cavernous malformations.
OBJECTIVE
The recognition of six unrelated Hispanic-American families in which cerebral cavernous malformations (CCM) segregated as an autosomal dominant trait established a genetic basis for this disease. Linkage analysis subsequently identified locus heterogeneity with disease genes for CCM at chromosomal regions 7q, 7p, and 3q. Recently, mutations in KRIT1, a gene on 7q at the CCM1 locus, were identified in French and Hispanic-American families with CCM. This study confirms the identity the KRIT1 founder mutation in Hispanic-Americans and reports a novel KRIT1 mutation in a Caucasian family.


METHODS
Oligonucleotide primers were designed to allow amplification of genomic DNA sequences from four Hispanic-American families and five non-Hispanic families for all 12 exons of the KRIT1 gene using the polymerase chain reaction (PCR). The amplified DNA was then screened using single strand conformation polymorphism analysis (SSCP) and sequencing. The expression pattern of KRIT1 was analyzed by Northern blotting.


RESULTS
Analysis of the KRIT1 gene revealed a point mutation in exon 6 that predicts the substitution of a premature termination codon for glutamine at codon 248 in all four Hispanic-American families, confirming previous findings. SSCP analysis and sequencing revealed an 11 base pair duplication in exon 7 leading to a premature termination codon in one Caucasian family. Northern analysis demonstrated widespread expression of this gene, however, the highest level of expression was in the brain.


CONCLUSIONS
The common KRIT1 mutation causing the majority of CCM in Hispanic-Americans has been identified and independently confirmed, allowing efficient presymptomatic molecular diagnosis. In keeping with prior results, both newly identified mutations create a premature termination codon and are predicted to initiate degradation of the mutant mRNA through the nonsense-mediated mRNA decay pathway. These data strongly suggest loss of function as the relevant patho-genetic mechanism.
Zhang
J
J
Howard Hughes Medical Institute and The Institute of Genetic Medicine, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA.
Clatterbuck
R E
RE
Rigamonti
D
D
Dietz
H C
HC
D001932:Brain Neoplasms / Q000235:genetics*; D002869:Chromosome Aberrations / Q000235:genetics*; D025063:Chromosome Disorders; D018703:Founder Effect; D005799:Genes, Dominant / Q000235:genetics*; D006392:Hemangioma, Cavernous / Q000235:genetics*; D006801:Humans; D000075927:KRIT1 Protein; D008869:Microtubule-Associated Proteins; D010375:Pedigree; D017354:Point Mutation / Q000235:genetics; D016133:Polymerase Chain Reaction; D018807:Polymorphism, Single-Stranded Conformational; D011518:Proto-Oncogene Proteins / Q000235:genetics*; D012333:RNA, Messenger / Q000235:genetics
D000075927:KRIT1 Protein; C107928:KRIT1 protein, human; D008869:Microtubule-Associated Proteins; D011518:Proto-Oncogene Proteins; D012333:RNA, Messenger