A rare cause of hyperphenylalaninemia: four cases from a single family with DNAJC12 deficiency

DNAJC12 in Monoamine Metabolism, Neurodevelopment, and Neurodegeneration

Recent studies show that pathogenic variants in DNAJC12, a co-chaperone for monoamine synthesis, may cause mild hyperphenylalaninemia with infantile dystonia, young-onset parkinsonism, developmental delay and cognitive deficits. DNAJC12 has been included in newborn screening, most revealingly in Spain, and those results highlight the importance of genetic diagnosis and early intervention in combating human disease. However, practitioners may be unaware of these advances and it is probable that many patients, especially adults, have yet to receive molecular testing for DNAJC12. Hence, this review summarizes genotype-phenotype relationships and treatment paradigms for patients with pathogenic variants in DNAJC12. It provides an overview of the structure of DNAJC12 protein, known genetic variants, domains, and binding partners, and elaborates on its role in monoamine synthesis, disease etiology, and pathogenesis. © 2023 International Parkinson and Movement Disorder Society.

DNAJC12 deficiency: Mild hyperphenylalaninemia and neurological impairment in two siblings

Background

DNAJC12 co-chaperone protein deficiency has been recently described as a stand-alone metabolic disorder explaining many cases of mild hyperphenylalaninemia (HPA) that are not caused by variants in the PAH gene, which encodes for the hepatic enzyme phenylalanine hydroxylase (PAH), or inGCH1, PTS, QDPR, PCBD1 and DHPR, involved in tetrahydrobiopterin (BH4) biosynthesis and activity.

Results

We describe two sisters born to consanguineous parents. The youngest sister (Patient 1), initially asymptomatic, tested positive at NewBorn Screening (NBS) for mild HPA. After variants in the PAH and BH4 related-genes were excluded, we performed DNAJC12 genetic analysis and found a previously described homozygous deletion [NM_021800.3: c.58_59del p.(Gly20Metfs*2)]. The older sister (Patient 2), homozygous for the same variant and exhibiting mild HPA, was diagnosed subsequently and presented with ataxia and repeated falls, upper limb dyskinesia, intentional tremor, and mild intellectual disability. Patient 1 was started on treatment with low Phenylalanine (Phe) diet, BH4, l-3,4-dihydroxyphenylalanine/carbidopa (L-DOPA) and 5-OH-Tryptophan, soon after diagnosis, and despite poor adherence to the dietary regimen, only manifested language impairment at last follow-up (age 5 years and 4 months). Patient 2, who started the same treatment at school age, experienced a minimal progression of neurological symptoms, with some improvement in her motor skills.

Conclusions

These two new patients with DNAJC12-associated HPA, in addition to previous reports, point to DNAJC12 deficiency as a new metabolic syndrome that must be considered in patients with unexplained HPA.