Heimler syndrome is a rare autosomal recessive disorder at the mild end of the peroxisomal biogenesis disorders (PBDs), characterized by sensorineural hearing loss, amelogenesis imperfecta, and retinal dystrophy. Nail abnormalities affect a minority. We present a 67-year-old woman diagnosed with non-syndromic retinitis pigmentosa in her fifties, who was later found to carry compound heterozygous variants in the PEX6 gene. Her medical history included prelingual hearing loss, early tooth decay, and brittle nails that were deemed unrelated for decades. Hearing loss and vision loss remained relatively stable up to last consultation. Our literature review includes 46 published Heimler syndrome cases with confirmed molecular diagnoses. Retinal dystrophy, predominantly of the rod-cone type with pigment clumping, was present in 89% of reported cases, with macular edema noted in 40%. Serum peroxisomal metabolite abnormalities seem to correlate with worse neurodevelopmental outcomes. There are no clear genotype-phenotype correlations, although residual peroxisomal function due to the presence of at least one missense, leaky splice site, or stable truncated allele explains the relatively mild phenotype for PBD. We underscore the importance to include syndromic disorders in the differential diagnosis of retinal dystrophy in older adults.

Zellweger syndrome (ZS) is a heterogeneous group of clinical conditions that commonly manifest with neurodevelopmental delay, multiple neurological abnormalities, visual and auditory impairments, and adrenocortical dysfunction. ZS is an autosomal recessive peroxisomal disorder resulting from mutations in one of over 13 identified genes. We report the case of a male child with episodic seizures starting at 18 days of life, followed by neurodevelopmental delay and neuroimaging findings of asymmetric polymicrogyria and cortical abnormalities. His healthy parents were consanguineous, and notably, a brother, who passed away at the age of 5 years-old, had epilepsy and adrenoleukodystrophy. Exome sequencing allowed the identification of a novel stop-loss homozygous variant in the PEX5 gene in the index case. The phenotype associated to this gene, Zellweger syndrome, as well as the inheritance mechanism, is consistent with that observed in both the patient and his brother.

Peroxisomal Biogenesis Disorders Zellweger Spectrum (PBD-ZSD) disorders are a group of autosomal recessive defects in peroxisome formation that produce a multi-systemic disease presenting at birth or in childhood. Well documented clinical biomarkers such as elevated very long chain fatty acids (VLCFA) are key biochemical diagnostic findings in these conditions. Additional, secondary biochemical alterations such as elevated very long chain lysophosphatidylcholines are allowing newborn screening for peroxisomal disease. In addition, a more widespread impact on metabolism and lipids is increasingly being documented by metabolomic and lipidomic studies. Here we utilize Drosophila models of pex2 and pex16 as well as human plasma from individuals with PEX1 mutations. We identify phospholipid abnormalities in Drosophila larvae and brain characterized by differences in the quantities of phosphatidylcholine (PC) and phosphatidylethanolamines (PE) with long chain lengths and reduced levels of intermediate chain lengths. For diacylglycerol (DAG), the precursor of PE and PC through the Kennedy pathway, the intermediate chain lengths are increased suggesting an imbalance between DAGs and PE and PC that suggests the two acyl chain pools are not in equilibrium. Altered acyl chain lengths are also observed in PE ceramides in the fly models. Interestingly, plasma from human subjects exhibit phospholipid alterations similar to the fly model. Moreover, human plasma shows reduced levels of sphingomyelin with 18 and 22 carbon lengths but normal levels of C24. Our results suggest that peroxisomal biogenesis defects alter shuttling of the acyl chains of multiple phospholipid and ceramide lipid classes. In contrast, DAG species with intermediate fatty acids are actually more abundant in PBD. These data suggest an imbalance between de novo synthesis of PC and PE through the Kennedy pathway and remodeling of existing PC and PE through the Lands cycle. This imbalance is likely due to overabundance of very long acyl chains in PBD and a subsequent imbalance due to substrate channeling effects. Given the fundamental role of phospholipid and sphingolipids in nervous system functions, these observations suggest PBD-ZSD are diseases characterized by widespread cell membrane lipid abnormalities.

Zellweger Spectrum Disorder (ZSD) is caused by defects in PEX genes, whose proteins are required for peroxisome assembly and function. Peroxisome dysfunction in ZSD causes multisystem effects, with progressive retinal degeneration (RD) among the most frequent clinical findings. However, much remains unknown about how peroxisome deficiency causes RD. To study RD pathophysiology in ZSD, we used the PEX1-p.Gly844Asp (G844D) mouse model, which represents the common human PEX1-p.Gly843Asp (G843D) variant. We previously reported diminished retinal function, diminished functional vision, and neural retina structural defects in this model. Here, we investigate the retinal pigment epithelium (RPE) phenotype, examining morphological, inflammatory, and lipid changes at 1, 3, and 6 months of age. We report that RPE cells exhibit evident degeneration by 3 months that worsens with time, starts in the dorsal pole, and is accompanied by subretinal inflammatory cell infiltration. We match these events with imaging mass spectrometry for regional analysis of lipids in the RPE. We identified 47 lipid alterations preceding structural changes, 9 of which localize to the dorsal pole. 29 of these persist to 3 months, with remodeling of the dorsal pole lipid signature. 13 new alterations occur concurrent with histological changes. Abnormalities in peroxisome-dependent lipids detected by LC/MS/MS are exacerbated over time. This study represents the first characterization of RPE in a ZSD model, and the first in situ lipid analysis in peroxisome-deficient tissue. Our findings uncover potential lipid drivers of RD progression in ZSD, and identify candidate biomarkers for retinopathy progression and response to therapy.

Peroxisome biogenesis disorders (PBD) affect multiple organ systems. It is characterized by neurological dysfunction, hypotonia, ocular anomalies, craniofacial abnormalities, and absence of peroxisomes in fibroblasts. PBDs are associated with mutations in any of fourteen different PEX genes, which are involved in peroxisome biogenesis. Zellweger spectrum disorder (ZSD) is a severe form of PBD. More than 90% of the ZSD cases have mutations in PEX1, PEX6, PEX10, PEX12, and PEX26. Mutations in the PEX19 gene are rarely associated with PBD/ZSD; however, a large proportion of PEX26 mutations are associated with ZSD. We recruited two Saudi families with multiple affected individuals with dysmorphic features, including hypertelorism, large open fontanelles, generalized hypotonia, and epicanthal folds with poor reflexes since birth. Whole exome sequencing (WES) and Sanger sequencing was performed to identify the genetic cause. The frequency and pathogenicity of the identified mutations were assessed using various online bioinformatics tools. WES identified a novel nonsense variant (c.367C > T) in the PEX19 gene in family A patients. This nonsense mutation was predicted to cause premature termination (p.Gln123*). A previously reported synonymous variant (c.228C > T; p.Gly76Gly) in PEX26 was found in a patient from family B. Both variants were segregating in an autosomal recessive manner in the respective families. The present study has added a novel nonsense mutation to the mutation spectrum of PEX19, which is the second null mutation identified to date. Moreover, in this study, the importance of a synonymous exonic variant of PEX26 close to the splice donor site was explored in relation to pre-mRNA splicing and resulting disease manifestations.