An Italian case of CADASIL with mutation CGC-TCG in codon 1006, exon 19 Notch3 gene

Mutational screening of NOTCH3 gene reveals two novel mutations: complexity of CADASIL diagnosis

Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) is an adult onset hereditary vascular disease with neurological manifestations. The classical clinical course is relentlessly progressive with early transient ischaemic attacks (TIA) or strokes, dementia and finally death in the mid-1960s. The disorder is inherited in an autosomal dominant fashion, with high penetrance and broad variable clinical course even within family. It is caused by mutations in the NOTCH3 gene; all causative mutations result in gain or loss of a cysteine residue within the extracellular domain, with exons 3 and 4 reported as hot spot mutational sites. Mutation analysis of the NOTCH3 gene was performed through direct sequencing of the 2-23 exons containing all EGF-like domains. Patients underwent genetic counselling pre and post testing. Here, we report two novel mutations located in exons 6 and 15 of the NOTCH3 gene; clinical description for the probands and for available relatives is enclosed. No reliable data on incidence or prevalence rates of this disease are available: it is therefore essential that the diagnosis is obtained in all suspected cases through the extensive analysis of the NOTCH3 gene and that all cases are brought to the attention of the scientific community.

NOTCH3 gene mutations in subjects clinically suspected of CADASIL

BACKGROUND

Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) is an inherited cerebrovascular disease due to mutations involving loss or gain of a cysteine residue in the NOTCH3 gene. A cluster of mutations around exons 3 and 4 was originally reported. Identification of pathogenic mutation is important for diagnostic confirmation of the disease, however genetic counselling and testing of relatives at risk is critical in mutation carriers.

METHODS

Mutation analysis of the NOTCH3 gene was performed through direct sequencing in 140 patients with clinical suspicion of CADASIL. Patients underwent genetic counselling pre and post testing. The 2-23 exons containing all EGF-like domains were screened.

RESULTS

14 familial forms of the disease have been identified with 14 different causative mutations in exons 2, 3, 4, 5, 7, 10, 14, 19, 20 and 22 of the NOTCH3 gene; no pathogenetic mutations have been identified in exons 6 and 8; several genetic variations both in coding as well as in intronic regions were identified too.

CONCLUSIONS

Our data confirm the importance of screening the whole EGF-like domains region of NOTCH3 gene for the molecular diagnosis of CADASIL among the Italian population too. Moreover genetic variants different from loss or gain of a cysteine residue are identified and presented.

Cerebral Autosomal Dominant Arteriopathy with Subcortical Infarcts and Leukoencephalopathy

Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) is an inherited autosomal dominant condition characterized by migrane, recurrent stroke, subcortical dementia, and pseudobulbar palsy. It begins with migraine with aura in -33% of patients. CADASIL is commonly overlooked or misdiagnosed owing to its recent identification. The pathological hallmark of angiopathy is the presence of multiple, small, deep cerebral infarcts, leucoencephalopathy, and nonatherorosclerotic, nonamyloid angiopathy involving mainly small, deep perforating cerebral arteries. Changes also are present in vascular smooth muscle cells and consist in the presence of granular osmiophilic material (GOM). The defective gene in CADASIL is Notch 3, which encodes a large transmembrane receptor. Magnetic resonance imaging shows high intensity signal lesions, often confluent, and areas of cystic degeneration of subcortical white matter and basal ganglia. Diagnostic strategies in CADASIL are matter of discussions because the electron microscopic demonstration of GOM was reported in 100% of symptomatic patients of French authors, but only in 45% of a British study. GOMs are not present in presymptomatic patients.