Peroxisome Biogenesis Disorders, Zellweger Syndrome Spectrum via the DNM1L Gene

Peroxisome Biogenesis Disorders, Zellweger Syndrome Spectrum (PBD-ZSS) consist of three related diseases Zellweger syndrome (ZS), neonatal adrenoleukodystrophy (NALD), and Infantile Refsum disease (IRD) that share overlapping phenotypes with severity ranging from ZS to IRD. The overall incidence of PBD-ZSS is estimated to be from 1:500,000 to 1:50,000 (Steinberg et al. 2012). Common clinical features to all three include neurodevelopmental delay, glaucoma, retinal dystrophy, impaired hearing, renal cysts, and hepatic dysfunction (Wanders and Waterham 2005). Zellweger syndrome (ZS) is the most severe with neonatal onset, and characterized by typical craniofacial dysmorphism and profound hypotonia, severe seizures, and inability to feed. Infants with ZS usually do not make any developmental progress and rarely survive the first year of life. Compared to ZS, patients with NALD have less severe hypotonia and seizures during infancy and may reach school age. IRD is the least severe form. Patients with IRD show variable developmental delay and often present predominantly with vision problems, sensorineural hearing loss, and liver dysfunction. Most affected patients can reach childhood and, in rare cases, survive into adulthood. It has been suggested that a peroxisome biogenesis disorder should be considered in any individuals manifesting both vision and hearing problems. Biochemical findings of a PBD-ZSS patient include elevated plasma VLCFAs (C24:0 and C26:0), phytanic acid, and pipecolate and deficient plasmalogen synthesis in erythrocytes or cultured fibroblasts. A disparity of biochemical results obtained from different specimens (plasma, cultured cells or tissues) has been reported in milder patients due to peroxisomal mosaicism. Treatments of PBD-ZSS focus on symptomatic therapy (Steinberg et al. 2012; Steinberg et al. 2006).

DNM1L encodes a member of the dynamin superfamily proteins mediating the division of both mitochondria and peroxisomes. Unlike typical PBD-ZSS, DNM1L pathogenic variants are reported to result in a lethal presentation in neonates characterized by defects in both mitochondria and peroxisomes. DNM1L-assocated diseases can be an autosomal dominant condition secondary to dominant-negative missense variants in the middle domain of the encoded protein (Waterham et al. 2007; Chang et al. 2010) or be a recessive disorder due to loss-of-function mutations (Yoon et al. 2014).

DNM1L pathogenic variants appear to be very rare and have only been reported in two families to date (Waterham et al. 2007; Yoon et al. 2014).

This test provides full coverage of all coding exons of the DNM1L gene plus 10 bases of flanking noncoding DNA in all available transcripts along with other non-coding regions in which pathogenic variants have been identified at PreventionGenetics or reported elsewhere. We define full coverage as >20X NGS reads or Sanger sequencing. PGnome panels typically provide slightly increased coverage over the PGxome equivalent. PGnome sequencing panels have the added benefit of additional analysis and reporting of deep intronic regions (where applicable).

Dependent on the sequencing backbone selected for this testing, discounted reflex testing to any other similar backbone-based test is available (i.e., PGxome panel to whole PGxome; PGnome panel to whole PGnome).