A novel gross deletion in the progranulin gene in four subjects with frontotemporal dementia

Mutations in progranulin gene (GRN) are a major cause of frontotemporal dementia (FTD). Most reported pathogenic mutations are nonsense, frameshift, or splicing mutations, resulting in a premature stop codon, degradation of mutated mRNA and consequent protein haploinsufficiency.

In this study, we analysed four subjects with FTD who had low plasma progranulin levels but no mutation detectable by sequencing of GRN, to disclose the underlying genetic cause of disease.

Multiplex ligation-dependent probe amplification (MLPA) method was applied to search for rearrangements in GRN. Region-specific polymerase chain reaction (PCR) and Sanger sequencing were performed to define the breakpoint. Quantitative real-time PCR (qRT-PCR) on GRN mRNA and haplotype sharing analysis were also performed.

MLPA revealed in all the subjects the same heterozygous deletion, and a possible common ancestor was suggested by haplotype sharing. PCR and sequencing allowed us to define the size of the deletion (3028 bp), that removes part of GRN promoter, exon 1 including the transcription start site and most of the intron 1, and the breakpoints. qRT-PCR showed reduced level of mRNA, confirming the pathological nature of the deletion.

In this study, we described a GRN heterozygous gross deletion which removes the consensus sequences for transcription factors and the transcription start site, leading to a reduced levels of plasma progranulin. Our study indicates that GRN rearrangements, although not common, should be investigated in patients with FTD who show low plasma progranulin levels but no GRN mutations detectable by DNA sequencing.