Background: Pontocerebellar hypoplasia type 1 (PCH1) is characterized by a central and peripheral motor dysfunction associated with anterior horn cell degeneration, similar to spinal muscular atrophy (SMA).
Objectives: We analysed three probands (later discovered to be siblings) suspected to have severe SMA, however, not confirmed by genetic test.
Methods: Clinical-exome analysis (Illumina) was performed to identify causative variants, followed by Sanger sequencing confirmation in probands and other 10 family members.
Results: Homozygous pathogenic variant c.92G>C (p.(Gly31Ala)) in the Exosome Component 3 (EXOSC3) gene was found in all 3 probands, thus confirming the diagnosis of a severe form of PCH1B. The parents and six siblings were carriers, while one sibling was homozygous for a reference allele. This variant is frequent in the Czech Roma population, where it is considered a founder mutation. Haplotype analysis in this largest reported PCH1B family showed that our patients inherited from their father (of Roma origin) a haplotype identical to that found in the Czech Roma population, thus indicating these alleles have a common origin.
Conclusion: This EXOSC3 variant is rare among the general population but most likely frequent also among Roma people in Slovakia. PCH1B should be considered for a differential diagnosis in infants manifesting SMA-like phenotype, especially if of Roma origin (Tab. 1, Fig. 1, Ref. 22). Text in PDF www.elis.sk Keywords: pontocerebellar hypoplasia, PCH1B, EXOSC3, SMA plus syndromes, pathogenic sequence variant.