Uniparental disomy of chromosome 16 unmasks recessive mutations of FA2H/SPG35 in 4 families.

July 12, 2016

Soehn AS1, Rattay TW1, Beck-Wödl S1, Schäferhoff K1, Monk D1, Döbler-Neumann M1, Hörtnagel K1, Schlüter A1, Ruiz M1, Pujol A1, Züchner S1, Riess O1, Schüle R1, Bauer P2, Schöls L1.


Identifying an intriguing mechanism for unmasking recessive hereditary spastic paraplegias.

Herein, we describe 4 novel homozygous FA2H mutations in 4 nonconsanguineous families detected by whole-exome sequencing or a targeted gene panel analysis providing high coverage of all known hereditary spastic paraplegia genes.

Segregation analysis revealed in all cases only one parent as a heterozygous mutation carrier whereas the other parent did not carry FA2H mutations. A macro deletion within FA2H, which could have caused a hemizygous genotype, was excluded by multiplex ligation-dependent probe amplification in all cases. Finally, a microsatellite array revealed uniparental disomy (UPD) in all 4 families leading to homozygous FA2H mutations. UPD was confirmed by microarray analyses and methylation profiling.

UPD has rarely been described as causative mechanism in neurodegenerative diseases. Of note, we identified this mode of inheritance in 4 families with the rare diagnosis of spastic paraplegia type 35 (SPG35). Since UPD seems to be a relevant factor in SPG35 and probably additional autosomal recessive diseases, we recommend segregation analysis especially in nonconsanguineous homozygous index cases to unravel UPD as mutational mechanism. This finding may bear major repercussion for genetic counseling, given the markedly reduced risk of recurrence for affected families.