Novel heterozygous OPA3 variant in a family with congenital cataracts, sensorineural hearing loss and neuropathy, without optic atrophy and comparison of pathogenic and population variants.

Heterozygous mutations in the OPA3 gene are associated with autosomal dominant optic atrophy-3 (OPA3), whereas biallelic mutations cause autosomal recessive 3-methylglutaconic aciduria type III. To date, all cases with pathogenic variants in the gene OPA3 have presented with optic atrophy. We report a large family with congenital cataracts, hearing loss and neuropathy, with a likely pathogenic novel missense variant in OPA3, c.30G>C; p.(Lys10Asn) that segregates with disease in the family pedigree. The family's clinical presentation has significant phenotypic overlap with previously reported cases of OPA3, except for a notable lack of optic atrophy. The analysis of all known disease-associated variants in OPA3 revealed an enrichment in missense variants in patients with OPA3 phenotype compared with loss-of-function variants, which are more likely to be observed in individuals with 3-methylglutaconic aciduria type III, supporting different mechanisms of disease. This case broadens the clinical and genetic spectrum associated with OPA3 mutations and highlights that optic atrophy is not an obligate feature of OPA3-related disorders.

Probing sesquiterpene hydroxylase activities in a coupled assay with terpene synthases.

5-epi-Aristolochene dihydroxylase (EAH) catalyzes unique stereo- and regiospecific hydroxylations of a bicyclic sesquiterpene hydrocarbon to generate capsidiol. To define functional and mechanistic features of the EAH enzyme, the utility of a coupled assay using readily available sesquiterpene synthases and microsomes from yeast overexpressing the EAH enzyme was determined. Capsidiol and deoxycapsidiol biosyntheses were readily measured in coupled assays consisting of 5-epi-aristolochene synthase and EAH as determined by the incorporation of radiolabeled farnesyl diphosphate into thin-layer chromatography-isolated products and verified by gas chromatography-mass spectrometry analysis. The assays were dependent on the amounts of synthase and hydroxylase protein added, the incubation times, and the presence of nicotinamide adenine dinucleotide phosphate. The utility of this coupled assay was extended by examining the relative efficiency of the EAH enzyme to catalyze hydroxylations of different sesquiterpene skeletons generated by other terpene synthases.