First Case of Peroxisomal D-bifunctional Protein Deficiency with Novel HSD17B4 Mutations and Progressive Neuropathy in Korea

Ataluren-mediated nonsense variant readthrough in D-bifunctional protein deficiency: A case report

D-bifunctional protein (DBP) deficiency, a fatal peroxisomal enzyme disorder, typically manifests with life-threatening symptoms in the first two years of childhood. We present the case of an infant with elevated lysophosphatidylcholine C26:0 (C26:0-LPC) levels identified during X-linked adrenoleukodystrophy (ALD) screening, leading to a diagnosis of DBP deficiency due to a homozygous HSD17B4 c.1041T>A, p.(Tyr347Ter) variant. Starting at two months of age, the infant experienced seizures, hypotonia, and developmental delays, prompting the initiation of experimental treatment with the readthrough agent PTC124 (ataluren) at six months. The treatment led to a decrease in C26:0-LPC levels from 0.65 μM to 0.53 μM; concomitant fish oil supplementation transiently increased C26:0-LPC to 0.74 μM before returning to 0.53 μM after cessation of supplementation. The patient demonstrated improved swallowing and progressive motor and speech development during a two-year treatment period, with no further seizures. This case report highlights the potential of nonsense readthrough therapy for peroxisomal disorders, a group of metabolic diseases that currently lack targeted treatments.

Overview of Neuro-Ophthalmic Findings in Leukodystrophies

Background: Leukodystrophies are a group of rare genetic diseases that primarily affect the white matter of the central nervous system. The broad spectrum of metabolic and pathological causes leads to manifestations at any age, most often in childhood and adolescence, and a variety of symptoms. Leukodystrophies are usually progressive, resulting in severe disabilities and premature death. Progressive visual impairment is a common symptom. Currently, no overview of the manifold neuro-ophthalmologic manifestations and visual impact of leukodystrophies exists. Methods: Data from 217 patients in the Hamburg leukodystrophy cohort were analyzed retrospectively for neuro-ophthalmologic manifestations, age of disease onset, and magnetic resonance imaging, visual evoked potential, and optical coherence tomography findings and were compared with data from the literature. Results: In total, 68% of the patients suffered from neuro-ophthalmologic symptoms, such as optic atrophy, visual neglect, strabismus, and nystagmus. Depending on the type of leukodystrophy, neuro-ophthalmologic symptoms occurred early or late during the course of the disease. Magnetic resonance imaging scans revealed pathologic alterations in the visual tract that were temporally correlated with symptoms. Conclusions: The first optical coherence tomography findings in Krabbe disease and metachromatic leukodystrophy allow retinal assessments. Comprehensive literature research supports the results of this first overview of neuro-ophthalmologic findings in leukodystrophies.

D-Bifunctional Protein Deficiency Diagnosis-A Challenge in Low Resource Settings: Case Report and Review of the Literature

D-bifunctional protein deficiency (D-BPD) is a rare, autosomal recessive peroxisomal disorder that affects the breakdown of long-chain fatty acids. Patients with D-BPD typically present during the neonatal period with hypotonia, seizures, and facial dysmorphism, followed by severe developmental delay and early mortality. While some patients have survived past two years of age, the detectable enzyme activity in these rare cases was likely a contributing factor. We report a D-BPD case and comment on challenges faced in diagnosis based on a narrative literature review. An overview of Romania's first patient diagnosed with D-BPD is provided, including clinical presentation, imaging, biochemical, molecular data, and clinical course. Establishing a diagnosis can be challenging, as the clinical picture is often incomplete or similar to many other conditions. Our patient was diagnosed with type I D-BPD based on whole-exome sequencing (WES) results revealing a pathogenic frameshift variant of the HSD17B4 gene, c788del, p(Pro263GInfs*2), previously identified in another D-BPD patient. WES also identified a variant of the SUOX gene with unclear significance. We advocate for using molecular diagnosis in critically ill newborns and infants to improve care, reduce healthcare costs, and allow for familial counseling.

DHA Shortage Causes the Early Degeneration of Photoreceptors and RPE in Mice With Peroxisomal β-Oxidation Deficiency

Purpose

Patients deficient in peroxisomal β-oxidation, which is essential for the synthesis of docosahexaenoic acid (DHA, C22:6n-3) and breakdown of very-long-chain polyunsaturated fatty acids (VLC-PUFAs), both important components of photoreceptor outer segments, develop retinopathy present with retinopathy. The representative mouse model lacking the central enzyme of this pathway, multifunctional protein 2 (Mfp2-/-), also show early-onset retinal decay and cell-autonomous retinal pigment epithelium (RPE) degeneration, accompanied by reduced plasma and retinal DHA levels. In this study, we investigated whether DHA supplementation can rescue the retinal degeneration of Mfp2-/- mice.

Methods

Mfp2+/- breeding pairs and their offspring were fed a 0.12% DHA or control diet during gestation and lactation and until sacrifice. Offspring were analyzed for retinal function via electroretinograms and for lipid composition of neural retina and plasma with lipidome analysis and gas chromatography, respectively, and histologically using retinal sections and RPE flatmounts at the ages of 4, 8, and 16 weeks.

Results

DHA supplementation to Mfp2-/- mice restored retinal DHA levels and prevented photoreceptor shortening, death, and impaired functioning until 8 weeks. In addition, rescue of retinal DHA levels temporarily improved the ability of the RPE to phagocytose outer segments and delayed the RPE dedifferentiation. However, despite the initial rescue of retinal integrity, DHA supplementation could not prevent retinal degeneration at 16 weeks.

Conclusions

We reveal that the shortage of a systemic supply of DHA is pivotal for the early retinal degeneration in Mfp2-/- mice. Furthermore, we report that adequate retinal DHA levels are essential not only for photoreceptors but also for RPE homeostasis.

The essential role of docosahexaenoic acid and its derivatives for retinal integrity

The fatty acid composition of photoreceptor outer segment (POS) phospholipids diverges from other membranes, being highly enriched in polyunsaturated fatty acids (PUFAs). The most abundant PUFA is docosahexaenoic acid (DHA, C22:6n-3), an omega-3 PUFA that amounts to over 50% of the POS phospholipid fatty acid side chains. Interestingly, DHA is the precursor of other bioactive lipids such as elongated PUFAs and oxygenated derivatives. In this review, we present the current view on metabolism, trafficking and function of DHA and very long chain polyunsaturated fatty acids (VLC-PUFAs) in the retina. New insights on pathological features generated from PUFA deficient mouse models with enzyme or transporter defects and corresponding patients are discussed. Not only the neural retina, but also abnormalities in the retinal pigment epithelium are considered. Furthermore, the potential involvement of PUFAs in more common retinal degeneration diseases such as diabetic retinopathy, retinitis pigmentosa and age-related macular degeneration are evaluated. Supplementation treatment strategies and their outcome are summarized.

Dysfunctional peroxisomal lipid metabolisms and their ocular manifestations

Retina is rich in lipids and dyslipidemia causes retinal dysfunction and eye diseases. In retina, lipids are not only important membrane component in cells and organelles but also fuel substrates for energy production. However, our current knowledge of lipid processing in the retina are very limited. Peroxisomes play a critical role in lipid homeostasis and genetic disorders with peroxisomal dysfunction have different types of ocular complications. In this review, we focus on the role of peroxisomes in lipid metabolism, including degradation and detoxification of very-long-chain fatty acids, branched-chain fatty acids, dicarboxylic acids, reactive oxygen/nitrogen species, glyoxylate, and amino acids, as well as biosynthesis of docosahexaenoic acid, plasmalogen and bile acids. We also discuss the potential contributions of peroxisomal pathways to eye health and summarize the reported cases of ocular symptoms in patients with peroxisomal disorders, corresponding to each disrupted peroxisomal pathway. We also review the cross-talk between peroxisomes and other organelles such as lysosomes, endoplasmic reticulum and mitochondria.

Two Novel HSD17B4 Heterozygous Mutations in Association With D-Bifunctional Protein Deficiency: A Case Report and Literature Review

Background: D-Bifunctional protein deficiency (D-BPD) is an autosomal recessive disorder caused by peroxisomal β-oxidation defects. According to the different activities of 2-enoyl-CoA hydratase and 3-hydroxyacyl-CoA dehydrogenase protein units, D-bifunctional protein defects can be divided into four types. The typical symptoms include hypotonia and seizures. The gene that encodes D-BP was HSD17B4, which is located in chromosome 5q23.1. Case Presentation: We report the first case of D-BPD in a Chinese patient with neonatal onset. Cosmetic malformations, severe hypotonia and seizures are prominent. The blood bile acid profile showed increased taurocholic acid, glycocholic acid, and taurochenodeoxycholic acid. Very-long-chain fatty acids (VLCFAs) revealed significant increases in hexacosanoic acid (C26:0), tetracosanoic acid/docosanoic acid (C24:0/C22:0), and hexacosanoic acid/docosanoic acid (C26:0/C22:0). Cranial MRI revealed bilateral hemispheric and callosal dysplasia, with schizencephaly in the right hemisphere. EEG showed loss of sleep-wake cycle and epileptiform discharge. Other examinations include abnormal brainstem auditory evoked potentials (BAEPs) and temporal pigmented spots on the optic disc in the right eye. After analysis by whole-exome sequencing, heterozygous c.972+1G>T in the paternal allele and c.727T>A (p.W243R) in the maternal allele were discovered. He was treated with respiratory support, formula nasogastric feeding, and antiepileptic therapy during hospitalization and died at home due to food refusal and respiratory failure at the age of 5 months. Conclusions: Whole-exome sequencing should be performed in time to confirm the diagnosis when the newborn presents hypotonia, seizures, and associated cosmetic malformations. There is still a lack of effective radical treatment. Supportive care is the main treatment, aiming at controlling symptoms of central nervous system like seizures and improving nutrition and growth. The disease has a poor outcome, and infants often die of respiratory failure within 2 years of age. In addition, heterozygous deletion variant c.972+1G>T and missense mutations c.727T>A (p.W243R) are newly discovered pathogenic variants that deserve further study.