Pathogenic variants of DNAJC12 and evaluation of the encoded cochaperone as a genetic modifier of hyperphenylalaninemia

This is the peer reviewed version of the following article: Pathogenic variants of DNAJC12 and evaluation of the encoded cochaperone as a genetic modifier of hyperphenylalaninemia. Human Mutation (2020): 25 April, which has been published in final form at [https://doi.org/10.1002/humu.24026. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived VersionsThe variants identified in this study are openly available at http://www.lovd.nl/ with reference numbers 0000644164, 0000645396, 0000644166, and 0000405673Biallelic variants of the gene DNAJC12, which encodes a cochaperone, were recently described in patients with hyperphenylalaninemia (HPA). This paper reports the retrospective genetic analysis of a cohort of unsolved cases of HPA. Biallelic variants of DNAJC12 were identified in 20 patients (generally neurologically asymptomatic) previously diagnosed with phenylalanine hydroxylase (PAH) deficiency (phenylketonuria [PKU]). Further, mutations of DNAJC12 were identified in four carriers of a pathogenic variant of PAH. The genetic spectrum of DNAJC12 in the present patients included four new variants, two intronic changes c.298‐2A>C and c.502+1G>C, presumably affecting the splicing process, and two exonic changes c.309G>T (p.Trp103Cys) and c.524G>A (p.Trp175Ter), classified as variants of unknown clinical significance (VUS). The variant p.Trp175Ter was detected in 83% of the mutant alleles, with 14 cases homozygous, and was present in 0.3% of a Spanish control population. Functional analysis indicated a significant reduction in PAH and its activity, reduced tyrosine hydroxylase stability, but no effect on tryptophan hydroxylase 2 stability, classifying the two VUS as pathogenic variants. Additionally, the effect of the overexpression of DNAJC12 on some destabilizing PAH mutations was examined and a mutation‐specific effect on stabilization was detected suggesting that the proteostasis network could be a genetic modifier of PAH deficiency and a potential target for developing mutation‐specific treatments for PKUThis work was funded by grant PI16/00573, B2017/BMD-3721, the Fundación Isabel Gemio and the Fundación La Caixa (LCF/PR/PR16/11110018), an institutional grant from the Fundación Ramón Areces to the Centro de Biología Molecular Severo Ochoa, and the European Regional Development Fun

Pathogenic variants of DNAJC12 and evaluation of the encoded cochaperone as a genetic modifier of hyperphenylalaninemia

Biallelic variants of the gene DNAJC12, which encodes a cochaperone, were recently described in patients with hyperphenylalaninemia (HPA). This paper reports the retrospective genetic analysis of a cohort of unsolved cases of HPA. Biallelic variants of DNAJC12 were identified in 20 patients (generally neurologically asymptomatic) previously diagnosed with phenylalanine hydroxylase (PAH) deficiency (phenylketonuria [PKU]). Further, mutations of DNAJC12 were identified in four carriers of a pathogenic variant of PAH. The genetic spectrum of DNAJC12 in the present patients included four new variants, two intronic changes c.298-2A>C and c.502+1G>C, presumably affecting the splicing process, and two exonic changes c.309G>T (p.Trp103Cys) and c.524G>A (p.Trp175Ter), classified as variants of unknown clinical significance (VUS). The variant p.Trp175Ter was detected in 83% of the mutant alleles, with 14 cases homozygous, and was present in 0.3% of a Spanish control population. Functional analysis indicated a significant reduction in PAH and its activity, reduced tyrosine hydroxylase stability, but no effect on tryptophan hydroxylase 2 stability, classifying the two VUS as pathogenic variants. Additionally, the effect of the overexpression of DNAJC12 on some destabilizing PAH mutations was examined and a mutation-specific effect on stabilization was detected suggesting that the proteostasis network could be a genetic modifier of PAH deficiency and a potential target for developing mutation-specific treatments for PKU.This work was funded by grant PI16/00573, B2017/BMD-3721, the Fundación Isabel Gemio and the Fundación La Caixa (LCF/PR/PR16/11110018), an institutional grant from the Fundación Ramón Areces to the Centro de Biología Molecular Severo Ochoa, and the European Regional Development Fund.Peer reviewe