Novel PEX1 mutations in fibroblasts from children with Zellweger spectrum disorders exhibit temperature sensitive characteristics.

Zellweger spectrum disorders (ZSD) are rare autosomal recessive disorders caused by defects in peroxisome biogenesis factor (PEX; peroxin) genes leading to impaired transport of peroxisomal proteins with peroxisomal targeting signals (PTS). Four patients, including a pair of homozygotic twins, diagnosed as ZSD by genetic study with different clinical presentations and outcomes as well as various novel mutations are described here. A total of 3 novel mutations, including a nonsense, a frameshift, and a splicing mutation, in PEX1 from ZSD patients were identified and unequivocally confirmed that the p.Ile989Thr mutant PEX1 exhibited temperature-sensitive characteristics and is associated with milder ZSD. The nature of the p.Ile989Thr mutant exhibited different characteristics from that of the other previously identified temperature-sensitive p.Gly843Asp PEX1 mutant. Transcriptome profiles under nonpermissive vs. permissive conditions were explored to facilitate the understanding of p.Ile989Thr mutant PEX1. Further investigation of molecular mechanisms may help to clarify potential genetic causes that could modify the clinical presentation of ZSD.

Liver disease predominates in a mouse model for mild human Zellweger spectrum disorder.

Zellweger spectrum disorders (ZSDs) are autosomal recessive diseases caused by defective peroxisome assembly. They constitute a clinical continuum from severe early lethal to relatively milder presentations in adulthood. Liver disease is a prevalent symptom in ZSD patients. The underlying pathogenesis for the liver disease, however, is not fully understood. We report a hypomorphic ZSD mouse model, which is homozygous for Pex1-c.2531G>A (p.G844D), the equivalent of the most common pathogenic variant found in ZSD, and which predominantly presents with liver disease. After introducing the Pex1-G844D allele by knock-in, we characterized homozygous Pex1-G844D mice for survival, biochemical parameters, including peroxisomal and mitochondrial functions, organ histology, and developmental parameters. The first 20 post-natal days (P20) were critical for survival of homozygous Pex1-G844D mice (~20% survival rate). Lethality was likely due to a combination of cholestatic liver problems, liver dysfunction and caloric deficit, probably as a consequence of defective bile acid biosynthesis. Survival beyond P20 was nearly 100%, but surviving mice showed a marked delay in growth. Surviving mice showed similar hepatic problems as described for mild ZSD patients, including hepatomegaly, bile duct proliferation, liver fibrosis and mitochondrial alterations. Biochemical analyses of various tissues showed the absence of functional peroxisomes accompanied with aberrant levels of peroxisomal metabolites predominantly in the liver, while other tissues were relatively spared. ur findings show that homozygous Pex1-G844D mice have a predominant liver disease phenotype, mimicking the hepatic pathology of ZSD patients, and thus constitute a good model to study pathogenesis and treatment of liver disease in ZSD patients.

A longitudinal study of retinopathy in the PEX1-Gly844Asp mouse model for mild Zellweger Spectrum Disorder.

Zellweger Spectrum Disorder (ZSD) is an autosomal recessive disease caused by mutations in any one of 13 PEX genes whose protein products are required for peroxisome assembly. Retinopathy leading to blindness is one of the major untreatable handicaps faced by patients with ZSD but is not well characterized, and the requirement for peroxisomes in retinal health is unknown. To address this, we examined the progression of retinopathy from 2 to 32 weeks of age in our murine model for the common human PEX1-p.Gly843Asp allele (PEX1-p.Gly844Asp) using electrophysiology, histology, immunohistochemistry, electron microscopy, biochemistry, and visual function tests. We found that retinopathy in male and female PEX1-G844D mice was marked by an attenuated cone function and abnormal cone morphology early in life, with gradually decreasing rod function. Structural defects at the inner retina occurred later in the form of bipolar cell degradation (between 13 and 32 weeks). Inner segment disorganization and enlarged mitochondria were seen at 32 weeks, while other inner retinal cells appeared preserved. Visual acuity was diminished by 11 weeks of age, while signal transmission from the retina to the brain was relatively intact from 7 to 32 weeks of age. Molecular analyses showed that PEX1-G844D is a subfunctional but stable protein, contrary to human PEX1-G843D. Finally, C26:0 lysophosphatidylcholine was elevated in the PEX1-G844D retina, while phopshoethanolamine plasmalogen lipids were present at normal levels. These characterization studies identify therapeutic endpoints for future preclinical trials, including improving or preserving the electroretinogram response, improving visual acuity, and/or preventing loss of bipolar cells.

Hepatic symptoms and histology in 13 patients with a Zellweger spectrum disorder.

Patients with a Zellweger spectrum disorder (ZSD) have a defect in the assembly or maintenance of peroxisomes, leading to a multisystem disease with variable outcome. Liver disease is an important feature in patients with severe and milder phenotypes and a frequent cause of death. However, the course and histology of liver disease in ZSD patients are ill-defined. We reviewed the hepatic symptoms and histological findings of 13 patients with a ZSD in which one or several liver biopsies have been performed (patient age 0.2-39 years). All patients had at least some histological liver abnormalities, ranging from minor fibrosis to cirrhosis. Five patients demonstrated significant disease progression with liver failure and early death. In others, liver-related symptoms were absent, although some still silently developed cirrhosis. Patients with peroxisomal mosaicism had a better prognosis. In addition, we show that patients are at risk to develop a hepatocellular carcinoma (HCC), as one patient developed a HCC at the age of 36 years and one patient a precancerous lesion at the age of 18 years. Thus, regular examination to detect fibrosis or cirrhosis should be included in the standard care of ZSD patients. In case of advanced fibrosis/cirrhosis expert consultation and HCC screening should be initiated. This study further delineates the spectrum and significance of liver involvement in ZSDs.

Zellweger syndrome with severe malnutrition, immunocompromised state and opportunistic infections.

Peroxisome biogenesis disorders are related to a spectrum of genetic diseases that range from severe Zellweger syndrome to milder infantile Refsum disease. Zellweger syndrome is characterised by dysmorphic features, severe hypotonia, seizures, failure to thrive, liver dysfunction and skeletal defects. Increased levels of very long chain fatty acids are the biochemical hallmark and the most common mutations found in the PEX1 gene. We report an unusual presentation of Zellweger syndrome in a 2-month-old female infant with severe malnutrition, opportunistic infections, lymphopaenia and a small thymic shadow on chest radiography. With this clinical picture, an initial hypothesis of primary immunodeficiency was considered. It was later confirmed to not be the case. On follow-up, global developmental delay, bilateral optic nerve atrophy and moderate bilateral sensorineural deafness grade II were documented. There were no further infectious complications and we concluded malnutrition was the cause of the infant's immunocompromised state.

Zellweger syndrome and secondary mitochondrial myopathy.

Defects in peroxisomes such as those associated with Zellweger syndrome (ZS) can influence diverse intracellular metabolic pathways, including mitochondrial functioning. We report on an 8-month-old female infant and a 6-month-old female infant with typical clinical, radiological and laboratory features of Zellweger syndrome; light microscopic and ultrastructural evidence of mitochondrial pathology in their muscle biopsies; and homozygous pathogenic mutations of the PEX16 gene (c.460 + 5G > A) and the PEX 12 gene (c.888_889 del p.Leu297Thrfs*12), respectively. Additionally, mitochondrial respiratory chain enzymology analysis in the first girl showed a mildly low activity in complexes II-III and IV. We also review five children previously reported in the literature with a presumptive diagnosis of ZS and additional mitochondrial findings in their muscle biopsies. In conclusion, this is the first study of patients with a molecularly confirmed peroxisomal disorder with features of a concomitant mitochondrial myopathy and underscores the role of secondary mitochondrial dysfunction in Zellweger syndrome, potentially contributing to the clinical phenotype.

High prevalence of primary adrenal insufficiency in Zellweger spectrum disorders.

Zellweger spectrum disorders are a group of autosomal recessive disorders characterized by impaired peroxisome functions. The clinical spectrum is broad, ranging from the classical most severe Zellweger syndrome to patients with a relatively mild phenotype. Treatment options are limited to symptomatic and supportive therapy. During routine follow-up we discovered patients with asymptomatic primary adrenal insufficiency. It is important to detect impaired adrenal function because it has treatment implications. Primary adrenal insufficiency was found in 7/24 patients examined, with 4/7 being asymptomatic. Systematic evaluation of adrenal function, through a Synacthen test, should be included in the clinical management of these patients.

Fetal echogenic bowel in association with Zellweger syndrome.

Increased echogenicity of fetal bowel in the second trimester obstetrical ultrasound has been described in association with several pathologic conditions, such as growth restriction, aneuploidy, cystic fibrosis, congenital infections, and gastrointestinal malformations. Zellweger syndrome (ZS) is the prototype of peroxisomal disorders characterized by craniofacial dysmorphism and severe neurologic abnormalities. We report two cases with fetal echogenic bowel (FEB) but no associated anomalies and normal fetal growth. After birth, clinical and laboratory findings led to diagnosis of ZS. Association of FEB with neurometabolic disorders is limited to a few case reports in the medical literature. To the best of our knowledge, this is the first report of ZS associated with FEB.

PEX13 deficiency in mouse brain as a model of Zellweger syndrome: abnormal cerebellum formation, reactive gliosis and oxidative stress.

Delayed cerebellar development is a hallmark of Zellweger syndrome (ZS), a severe neonatal neurodegenerative disorder. ZS is caused by mutations in PEX genes, such as PEX13, which encodes a protein required for import of proteins into the peroxisome. The molecular basis of ZS pathogenesis is not known. We have created a conditional mouse mutant with brain-restricted deficiency of PEX13 that exhibits cerebellar morphological defects. PEX13 brain mutants survive into the postnatal period, with the majority dying by 35 days, and with survival inversely related to litter size and weaning body weight. The impact on peroxisomal metabolism in the mutant brain is mixed: plasmalogen content is reduced, but very-long-chain fatty acids are normal. PEX13 brain mutants exhibit defects in reflex and motor development that correlate with impaired cerebellar fissure and cortical layer formation, granule cell migration and Purkinje cell layer development. Astrogliosis and microgliosis are prominent features of the mutant cerebellum. At the molecular level, cultured cerebellar neurons from E19 PEX13-null mice exhibit elevated levels of reactive oxygen species and mitochondrial superoxide dismutase-2 (MnSOD), and show enhanced apoptosis together with mitochondrial dysfunction. PEX13 brain mutants show increased levels of MnSOD in cerebellum. Our findings suggest that PEX13 deficiency leads to mitochondria-mediated oxidative stress, neuronal cell death and impairment of cerebellar development. Thus, PEX13-deficient mice provide a valuable animal model for investigating the molecular basis and treatment of ZS cerebellar pathology.

Germinal matrix hemorrhage in Zellweger syndrome.

A term male newborn was noted to have severe diffuse hypotonia, hyporeflexia, hepatosplenomegaly, and characteristic abnormal facies of Zellweger syndrome, the diagnosis of which was confirmed by identification of 2 mutations including Nt2098insT, a frameshift with premature stop codon in exon 13, as well as a novel second mutation at Nt3038G→A (Arg1013His) on skin fibroblast testing. His brain magnetic resonance imaging (MRI) demonstrated bilateral germinolytic cysts with unilateral hemorrhagic transformation. Germinolytic cysts are one of the characteristic radiographic features of Zellweger syndrome, but germinal matrix hemorrhage has never been reported. Germinal matrix hemorrhage is common in premature infants, but found in only 4% of normal term infants. Germinal matrix hemorrhage was seen in a case of Zellweger syndrome with a novel mutation.

Corneal ulceration due to vitamin A deficiency in Zellweger syndrome.

We report a case of vitamin A deficiency and secondary corneal ulcer in an infant with Zellweger syndrome. A 7-month-old infant with failure to thrive and malnutrition developed a corneal ulcer. Fortified antibiotic eye drops were administered without improvement. Vitamin A deficiency was suspected and confirmed. Supplementation with oral vitamin A decreased corneal opacification. Zellweger syndrome was later diagnosed. Vitamin A deficiency should be considered in the differential diagnosis of nonhealing corneal ulcers in children, especially those with systemic syndromes and failure to thrive.

High incidence of hyperoxaluria in generalized peroxisomal disorders.

The Zellweger spectrum disorders (ZSDs) are characterized by a generalized loss of peroxisomal functions caused by deficient peroxisomal assembly. Clinical presentation and survival are heterogeneous. Although most peroxisomal enzymes are unstable in the cytosol of peroxisome-deficient cells of ZSD patients, a few enzymes remain stable among which alanine:glyoxylate aminotransferase (AGT). Its deficiency causes primary hyperoxaluria type 1 (PH1, MIM 259900), an inborn error of glyoxylate metabolism characterized by hyperoxaluria, nephrocalcinosis, and renal insufficiency. Despite the normal level of AGT activity in ZSD patients, hyperoxaluria has been reported in several ZSD patients. We observed the unexpected occurrence of renal stones in a cohort of ZSD patients. This led us to perform a study in this cohort to determine the prevalence of hyperoxaluria in ZSDs and to find clinically relevant clues that correlate with the urinary oxalate load. We reviewed medical charts of 31 Dutch ZSD patients with prolonged survival (>1 year). Urinary oxalate excretion was assessed in 23 and glycolate in 22 patients. Hyperoxaluria was present in 19 (83%), and hyperglycolic aciduria in 14 (64%). Pyridoxine treatment in six patients did not reduce the oxalate excretion as in some PH1 patients. Renal involvement with urolithiasis and nephrocalcinosis was present in five of which one developed end-stage renal disease. The presence of hyperoxaluria, potentially leading to severe renal involvement, was statistically significant correlated with the severity of neurological dysfunction. ZSD patients should be screened by urinalysis for hyperoxaluria and renal ultrasound for nephrocalcinosis in order to take timely measures to prevent renal insufficiency.

Recognition of Zellweger syndrome in infancy.

At least 29 proteins are required for assembly of the peroxisome, a single-membrane organelle responsible for many metabolic processes. A defect in any of these proteins affects the numerous biochemical functions of the cell. Many genetic disorders are associated with peroxisome defects. Zellweger syndrome, a rare autosomal recessive disorder, is one of the disorders that result from a deficiency in the assembly of the peroxisome. Impaired metabolism results in the accumulation of toxic metabolites and damages developing neural cells. This article provides an overview of peroxisome function and its effect on central nervous system development. It highlights the presentation, clinical features, and nursing care of infants with Zellweger syndrome. A meticulous systematic physical assessment enhances early recognition of the physical features of this disorder. Although magnetic resonance imaging detects polymicrogyria, a manifestation of abnormal neuronal migration that is often associated with Zellweger syndrome, the diagnosis is confirmed biochemically. An emphasis on family support through genetic counseling and the integration of palliative resources to enhance quality of life for infants and families with this lethal condition is provided.