DNACJ12 deficiency in patients with unexplained hyperphenylalaninemia: two new patients and a novel variant

In addition to tetrahydrobiopterin deficiencies and phenylalanine hydroxylase deficiency (phenylketonuria) due to PAH variants, the deficiency of the co-chaperone protein DNAJC12 was identified in 2017 as a novel cause of inherited hyperphenylalaninemia, revealing the genetic etiology in previously unresolved cases. In this study, we aimed to investigate DNAJC12 deficiency in non-tetrahydrobiopterin-deficient persistent hyperphenylalaninemia cases without biallelic PAH variants in a single pediatric metabolic center. It was determined retrospectively that 471 patients with non-tetrahydrobiopterin deficiency-hyperphenylalaninemia had undergone PAH gene sequencing and 451 patients had biallelic variants in PAH. DNAJC12 sequencing was performed in the remaining 20 patients, identifying a previously reported homozygous splice-site variant (c.158-2A > T) in one patient with axial hypotonia and developmental delay, and a novel, homozygous c.404del (p.Arg135Lysfs*21) frameshift variant in an asymptomatic patient. In segregation analysis, the asymptomatic patient's both parents were also found to be homozygous for this variant and hyperphenylalaninemic. The parents may have had academic difficulties but intellectual disability could not be confirmed due to lack of cooperation. The symptomatic patient significantly benefited from treatment with sapropterin dihydrochloride and neurotransmitter precursors. DNAJC12 deficiency might be responsible for approximately 10% or more of cases with unexplained hyperphenylalaninemia. The phenotypic spectrum is broad, ranging from early infantile hypotonia to incidental diagnosis in adulthood. Similar to tetrahydrobiopterin deficiencies, early diagnosis and treatment with sapropterin dihydrochloride and neurotransmitter precursors can be beneficial, supporting the analysis of DNACJ12 gene in patients with unexplained hyperphenylalaninemia.

Correction to: DNAJC12 deficiency in patients with unexplained hyperphenylalaninemia: two new patients and a novel variant

A Correction to this paper has been published: https://doi.org/10.1007/s11011-021-00759-8.

Cognitive and behavioral impairment in mild hyperphenylalaninemia

Evinç SG, Pektaş E, Foto-Özdemir D, Yıldız Y, Karaboncuk Y, Bilginer-Gürbüz B, Dursun A, Tokatlı A, Coskun T, Öktem F, Sivri HS. Cognitive and behavioral impairment in mild hyperphenylalaninemia. Turk J Pediatr 2018; 60: 617-624. As elevated phenylalanine (Phe) is detrimental to brain functions, determining a safe upper limit of blood Phe is important for initiation of treatment plans and setting Phe targets in hyperphenlalaninemic patients. It is accepted that Phe levels below 360 μmol/L does not impair brain function and hence does not require treatment. Therefore, we aimed to compare cognitive functions and attention-related problems among healthy children and untreated patients with hyperphenylalaninemia (HPA). This study included 41 hyperphenylalaninemic patients (`all HPA group`) aged 6-16 years with untreated blood Phe between 240 and 600 μmol/L and 29 healthy controls. `All HPA group` was further divided into 2 subgroups according to their lifetime median blood Phe levels as `Phe 360-600 μmol/L` and `Phe 240-360 μmol/L` groups. Wechsler Intelligence Scale for Children-IV (WISC-IV), Conners` Continuous Performance Test (CPT), Strength and Difficulties Questionnaire (SDQ) and Schedule for Affective Disorders and Schizophrenia for School-Age Children: Present and Lifetime Version (K-SADS-PL) were performed as a comprehensive neurocognitive, attention and behavioral assessment. The study illustrated that `all HPA` patients had significantly lower scores on all WISC-IV indexes compared to controls, except for Working Memory. Both `Phe 360-600 μmol/L` and `Phe 240-360 μmol/L` subgroups had lower Full Scale intelligence quotient (IQ) and Verbal Comprehension scores compared to controls. `All HPA` patients also had longer reaction times and more peer problems than controls, indicating attention deficits and behavioral problems. Since the results demonstrated that children with untreated Phe levels between 240-360 μmol/L are at higher risk for cognitive and attention-related problems, lowering the `safe` upper Phe level should be considered.