Optic neuropathy

Gene: PPIB

I don't know

Comment on list classification: There is emerging evidence for the association of optic neuropathy and monoallelic variants in PPIB. 19 individuals from 9 families, affected by isolated optic neuropathy, were heterozygous for the same variant in PPIB: c.538C>T, p.(Arg180Trp) - PMID: 41045073. As 8/9 families are of European (Austrian) origins, a founder variant effect cannot be excluded.
Moreover, biallelic variants in PPIB have previously been implicated in severe skeletal dysplasia / osteogenesis imperfecta, with no mention of optic atrophy symptoms in the heterozygous family members (PMID: 21282188). Based on the available evidence, this gene-disease association is ambiguous and should be rated as Amber.

Created: 28 Oct 2025, 4:32 p.m. | Last Modified: 28 Oct 2025, 4:33 p.m.

Panel Version: 5.26

PMID: 41045073 Valentin et al., 2025 (journal pre-proof)
Authors report 19 individuals from 9 families (8 European / Austrian and 1 East Asian / Thai) affected by isolated optic neuropathy. Affected individuals were heterozygous for PPIB [NM_000942.5:c.538C>T, p.(Arg180Trp)]. Sequencing method: exome sequencing. Median age of onset was 36 years old (range 14-58 yo), with variable severity. Haplotype analysis revealed that the variant in PPIB is present on a common ancestral haplotype in 5/9 families.
In addition, genotyping of family members revealed 6 unaffected individuals were heterozygous for p.(Arg180Trp). Age range: 6-26 years old - possibly assessed before onset of disease.
The mRNA and protein levels were the same between fibroblasts of affected and unaffected members. Mitochondrial morphology investigation showed that affected individuals had a higher proportion of fragmented, 'balloon-like' mitochondria. Some evidence of decreased respiration rate and ATP production rate in affected individuals.
PPIB [NM_000942.5:c.538C>T, p.(Arg180Trp) - Revel score = 0.16 (Benign); rare in gnomAD v4, 7 heterozygotes reported. The variant lies in the last exon of PPIB at the end of the predicted Pro_isomerase functional domain (Decipher).

PMID: 21282188 Pyott et al., 2011
3 families with individuals affected by osteogenesis imperfecta, with biallelic variants in PPIB.
Family 1: c.120delC, p.(Val42SerfsX16), P1 and affected sister homozygous, parents confirmed heterozygous.
Family 2: 2 siblings compound heterozygous for c.414_423del, p.(Ser139Thrfs*21) and c.313G>A, p.(Gly105Arg). Parents confirmed heterozygous for one allele each.
Family 3: proband homozygous for c.343+1G>A, p.(Gly115delins10) - parents not genotyped.
Expression studies of mutant transcripts confirmed that mRNA and/or protein levels were unstable. Heterozygous parents were reported to be unaffected.

Created: 28 Oct 2025, 4:24 p.m. | Last Modified: 11 Nov 2025, 9:32 a.m.

Panel Version: 5.26

Mode of inheritance
MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown

Phenotypes
optic atrophy, MONDO:0003608

Publications

• 21282188
• 41045073