Intragenic CNVs Lead to Hereditary Spastic Paraplegia via a Haploinsufficiency Mechanism.

The most common form of hereditary spastic paraplegia (HSP), SPG4 is caused by single nucleotide variants and microrearrangements in the gene. The high percentage of multi-exonic deletions or duplications observed in SPG4 patients is predisposed by the presence of a high frequency of sequences in the gene sequence. In the present study, we analyzed DNA and RNA samples collected from patients with different microrearrangements in to map gene breakpoints and evaluate the mutation mechanism. The study group consisted of 69 individuals, including 50 SPG4 patients and 19 healthy relatives from 18 families. Affected family members from 17 families carried varying ranges of microrearrangements in the gene, while one individual had a single nucleotide variant in the 5'UTR of . To detect the breakpoints of the gene, long-range PCR followed by sequencing was performed. The breakpoint sequence was detected for five different intragenic deletions and one duplication, revealing -mediated microhomology at breakpoint junctions resulting from non-allelic homologous recombination in these patients. Furthermore, gene expression analysis was performed using patient RNA samples extracted from whole blood. Quantitative real-time PCR tests performed in 14 patients suggest no expression of transcripts with microrearrangements in 5 of them. The obtained data indicate that nonsense-mediated decay degradation is not the only mechanism of hereditary spastic paraplegia in patients with microrearrangements.