Pharmacodynamics, safety, tolerability and pharmacokinetics of a single oral dose of an engineered phenylalanine ammonia-lyase in patients with phenylketonuria

The cornerstone treatment of hyperphenylalaninemia (HPA) and phenylketonuria (PKU) is a lifelong low-protein diet with phenylalanine (Phe) free L-amino acid supplements. However, the PKU diet has significant shortcomings, and there is a clinically unmet need for new therapeutics to improve patient outcomes. CDX-6114 is a modified phenylalanine ammonia-lyase (PAL) enzyme obtained by a mutation in the Anabaena variabilis PAL sequence. CodeEvolver® protein engineering technology has been applied to improve the degradation resistance of the enzyme. In our first phase I trial, 19 patients were given a single oral dose of CDX-6114 at 7.5 g, 2.5 g, 0.7 g, or placebo in a cross-over design. After an overnight fast, patients received a standardised breakfast of 20 g of protein, thus exceeding the dietary recommendations for a single meal in patients with PKU. Plasma levels of Phe and cinnamic acid (CA) were measured over a 5-h period following CDX-6114 dosing. During the development of CDX-6114, a stability assessment using reverse-phase high-performance liquid chromatography (HPLC) assay revealed two peaks. The second peak was identified as CA. It was not previously known that as part of the mechanism of action, the CA remained associated with the protein following the conversion of Phe. Thus, recalculating the historical PAL enzyme amounts in CDX-6114 bulk substance was necessary. An updated extinction coefficient was achieved by applying a correction factor of 0.771 to previously reported doses. Postprandial plasma levels of Phe increased in all dose cohorts over time between 10% and 30% from baseline, although the actual peak of Phe levels was not achieved within the 5-h observation. When accounting for the interquartile ranges, these concentrations were similar to the placebo. As plasma levels of Phe were no longer a reliable marker for pharmacodynamics, the consistently detectable amount of CA seen in all patients who received CDX-6114 provided proof of the enzymatic activity of CDX-6114 in metabolising gastrointestinal Phe. Peak levels of CA were seen shortly after CDX-6114 intake, with a rapid decline, and remained low compared with the plasma Phe levels. This pattern indicates a short half-life, possibly due to the liquid formulation or the inability to withstand the lower pH in the human stomach compared with animal models in earlier studies. This was the first trial in patients with PKU to establish the safety and tolerability of CDX-6114. A single dose of CDX-6114 was safe and well tolerated, with no serious adverse events or presence of anti-drug antibodies detected. Efficacy will be explored in future trials using an optimised formulation.

Expert Consensus on the Long-Term Effectiveness of Medical Nutrition Therapy and Its Impact on the Outcomes of Adults with Phenylketonuria

Many adults with phenylketonuria (PKU) rely on medical nutrition therapy (MNT; low phenylalanine (Phe) diet with protein substitutes/medical foods) to maintain blood Phe concentrations within recommended ranges and prevent PKU-associated comorbidities. Despite disease detection through newborn screening and introduction of MNT as early as birth, adherence to MNT often deteriorates from childhood onwards, complicating the assessment of its effectiveness in the long term. Via a modified Delphi process, consensus (≥70% agreement) was sought on 19 statements among an international, multidisciplinary 13-member expert panel. After three iterative voting rounds, the panel achieved consensus on 17 statements related to the limitations of the long-term effectiveness of MNT (7), the burden of long-term reliance on MNT (4), and its potential long-term detrimental health effects (6). According to the expert panel, the effectiveness of MNT is limited in the long term, is associated with a high treatment burden, and demonstrates that adults with PKU are often unable to achieve metabolic control through dietary management alone, creating an unmet need in the adult PKU population.

Triple P for Parents of Children with Phenylketonuria: A Nonrandomized Trial

OBJECTIVE

Families of children with phenylketonuria (PKU) report child emotional and behavioral problems, parenting stress, and parenting difficulties, which are associated with worse health-related quality of life. This study aimed to examine acceptability and feasibility of a brief, group-based parenting program (Healthy Living Triple P) for families of children with PKU.

METHODS

An uncontrolled nonrandomized trial design was used. Families of children aged 2-12 years (N = 17) completed questionnaire measures assessing child behavior and impact of PKU on quality of life (primary outcomes), and parenting behavior, self-efficacy and stress, and children's behavioral and emotional adjustment (secondary outcomes). Routinely collected blood phenylalanine (Phe) levels were obtained from the treating team. Parents selected two child behaviors as targets for change. The intervention comprised two, 2-hr group sessions delivered face-to-face or online. Assessment was repeated at 4-week postintervention (T2) and 4-month follow-up (T3).

RESULTS

Attrition was low and parent satisfaction with the intervention (face-to-face and online) was high. All families achieved success with one or both child behavior goals, and 75% of families achieved 100% success with both behavior goals by T3; however, there was no change in health-related quality of life. There were moderate improvements in parent-reported ineffective parenting (total score, d = 0.87, 95% CI -1.01 to 2.75) and laxness (d = 0.59, 95% CI -1.27 to 2.46), but no effects on parenting stress or children's adjustment. Phe levels improved by 6month post-intervention for children with elevated preintervention levels.

CONCLUSIONS

Results support intervention acceptability and feasibility. A randomized controlled trial is warranted to establish intervention efficacy.

Psychosocial functioning in children with phenylketonuria: Relationships between quality of life and parenting indicators

OBJECTIVE

This study aimed to assess the impact of phenylketonuria (PKU) and its treatment on parent and child health-related quality of life (HRQoL) and to identify the parenting-related correlates of parent and child HRQoL, as well as metabolic control.

METHODS

Eighteen mothers of 2- to 12-year-old children with PKU participated and completed a series of self-report questionnaires including the PKU Impact and Treatment Quality of Life Questionnaire (PKU-QOL).

RESULTS

Mothers reported that the most significant impact of PKU on HRQoL was in relation to the impact of their child's anxiety during blood tests on their own HRQoL and guilt related to poor adherence to dietary restrictions and supplementation regimens. Higher reported intensity of child emotional and behavioural difficulties and parenting stress were associated with higher scores for PKU symptoms on the PKU-QOL, higher scores for emotional, social, and overall impact of PKU, and higher scores for the impact of dietary restriction. Where mothers reported greater use of overreactivity as a parenting strategy, children tended to have better lifetime phenylalanine levels; however, the overall impact of PKU and the impact of supplement administration on mothers' HRQoL were worse for these families.

CONCLUSIONS

These findings have implications for a holistic family-centred approach to the care of children with PKU and their families.

Squalene Synthase Deficiency: Clinical, Biochemical, and Molecular Characterization of a Defect in Cholesterol Biosynthesis

Mendelian disorders of cholesterol biosynthesis typically result in multi-system clinical phenotypes, underlining the importance of cholesterol in embryogenesis and development. FDFT1 encodes for an evolutionarily conserved enzyme, squalene synthase (SS, farnesyl-pyrophosphate farnesyl-transferase 1), which catalyzes the first committed step in cholesterol biosynthesis. We report three individuals with profound developmental delay, brain abnormalities, 2-3 syndactyly of the toes, and facial dysmorphisms, resembling Smith-Lemli-Opitz syndrome, the most common cholesterol biogenesis defect. The metabolite profile in plasma and urine suggested that their defect was at the level of squalene synthase. Whole-exome sequencing was used to identify recessive disease-causing variants in FDFT1. Functional characterization of one variant demonstrated a partial splicing defect and altered promoter and/or enhancer activity, reflecting essential mechanisms for regulating cholesterol biosynthesis/uptake in steady state.

Recurrent Muscle Weakness with Rhabdomyolysis, Metabolic Crises, and Cardiac Arrhythmia Due to Bi-allelic TANGO2 Mutations

The underlying genetic etiology of rhabdomyolysis remains elusive in a significant fraction of individuals presenting with recurrent metabolic crises and muscle weakness. Using exome sequencing, we identified bi-allelic mutations in TANGO2 encoding transport and Golgi organization 2 homolog (Drosophila) in 12 subjects with episodic rhabdomyolysis, hypoglycemia, hyperammonemia, and susceptibility to life-threatening cardiac tachyarrhythmias. A recurrent homozygous c.460G>A (p.Gly154Arg) mutation was found in four unrelated individuals of Hispanic/Latino origin, and a homozygous ∼34 kb deletion affecting exons 3-9 was observed in two families of European ancestry. One individual of mixed Hispanic/European descent was found to be compound heterozygous for c.460G>A (p.Gly154Arg) and the deletion of exons 3-9. Additionally, a homozygous exons 4-6 deletion was identified in a consanguineous Middle Eastern Arab family. No homozygotes have been reported for these changes in control databases. Fibroblasts derived from a subject with the recurrent c.460G>A (p.Gly154Arg) mutation showed evidence of increased endoplasmic reticulum stress and a reduction in Golgi volume density in comparison to control. Our results show that the c.460G>A (p.Gly154Arg) mutation and the exons 3-9 heterozygous deletion in TANGO2 are recurrent pathogenic alleles present in the Latino/Hispanic and European populations, respectively, causing considerable morbidity in the homozygotes in these populations.

Identifying the need for a multidisciplinary approach for early recognition of mucopolysaccharidosis VI (MPS VI)

Mucopolysaccharidosis VI (MPS VI, Maroteaux-Lamy syndrome) is caused by deficient activity of the enzyme, N-acetylgalactosamine-4-sulfatase, resulting in impaired degradation of the glycosaminoglycan dermatan sulfate. Patients experience a range of manifestations including joint contractures, short stature, dysostosis multiplex, coarse facial features, decreased pulmonary function, cardiac abnormalities, corneal clouding and shortened life span. Recently, clinicians from institutions in the Asia-Pacific region met to discuss the occurrence and implications of delayed diagnosis and misdiagnosis of MPS VI in the patients they have managed. Eighteen patients (44% female) were diagnosed. The most common sign presented by the patients was bone deformities in 11 patients (65%). Delays to diagnosis occurred due to the lack of or distance to diagnostic facilities for four patients (31%), alternative diagnoses for two patients (15%), and misleading symptoms experienced by two patients (15%). Several patients experienced manifestations that were subtler than would be expected and were subsequently overlooked. Several cases highlighted the unique challenges associated with diagnosing MPS VI from the perspective of different specialties and provide insights into how these patients initially present, which may help to elucidate strategies to improve the diagnosis of MPS VI.

Overcoming the barriers to diagnosis of Morquio A syndrome

Background

Morquio A syndrome is an autosomal recessive lysosomal storage disease often resulting in life-threatening complications. Early recognition and proficient diagnosis is imperative to facilitate prompt treatment and prevention of clinical complications.

Methods

Experts in Asia Pacific reviewed medical records focusing on presenting signs and symptoms leading to a diagnosis of Morquio A syndrome.

Results

Eighteen patients (77% female) had a mean (median; min, max) age of 77.1 (42.0; 0.0, 540.0) months at symptom onset, 78.9 (42.0; 4.5, 540.0) months at presentation and 113.8 (60.0; 7.0, 540.0) months at diagnosis. Orthopedic surgeons and pediatricians were most frequently consulted pre-diagnosis while clinical geneticists/metabolic specialists most frequently made the diagnosis. Delayed diagnoses were due to atypical symptoms for 5 patients (28%), while 4 patients (22%) experienced each of subtle symptoms, symptoms commonly associated with other diseases, or false-negative urine glycosaminoglycan analysis. Two patients (11%) each experienced overgrowth within the first year of life. Two patients with Morquio A syndrome (11%) were diagnosed with craniosynostosis and 1 (6%) for each of Legg-Calvé-Perthes disease, Leri-Weill syndrome, and pseudoachondroplasia. Early radiographic features of Morquio A syndrome led to more efficient diagnosis.

Conclusions

Increased awareness of clinical symptomology overlapping with Morquio A syndrome is essential. Clinicians encountering patients with certain skeletal dysplasia should consider Morquio A syndrome in their differential diagnosis. Atypical or subtle symptoms should not eliminate Morquio A syndrome from the differential diagnosis, especially for patients who may have non-classical phenotype of Morquio A syndrome.