Variants in NGLY1 lead to intellectual disability, myoclonus epilepsy, sensorimotor axonal polyneuropathy and mitochondrial dysfunction

NGLY1 encodes the enzyme N‐glycanase that is involved in the degradation of glycoproteins as part of the endoplasmatic reticulum‐associated degradation pathway. Variants in this gene have been described to cause a multisystem disease characterized by neuromotor impairment, neuropathy, intellectual disability, and dysmorphic features. Here, we describe four patients with pathogenic variants in NGLY1. As the clinical features and laboratory results of the patients suggested a multisystem mitochondrial disease, a muscle biopsy had been performed. Biochemical analysis in muscle showed a strongly reduced ATP production rate in all patients, while individual OXPHOS enzyme activities varied from normal to reduced. No causative variants in any mitochondrial disease genes were found using mtDNA analysis and whole exome sequencing. In all four patients, variants in NGLY1 were identified, including two unreported variants (c.849T>G (p.(Cys283Trp)) and c.1067A>G (p.(Glu356Gly)). Western blot analysis of N‐glycanase in muscle and fibroblasts showed a complete absence of N‐glycanase. One patient showed a decreased basal and maximal oxygen consumption rates in fibroblasts. Mitochondrial morphofunction fibroblast analysis showed patient specific differences when compared to control cell lines. In conclusion, variants in NGLY1 affect mitochondrial energy metabolism which in turn might contribute to the clinical disease course.

Identification and Characterization of New Variants in FOXRED1 Gene Expands the Clinical Spectrum Associated with Mitochondrial Complex I Deficiency

Complex I (nicotinamide adenine dinucleotide (NADH): ubiquinone oxidoreductase) is the largest complex of the mitochondrial oxidative phosphorylation system (OXPHOS) system. Forty-four subunits encoded in nuclear and mitochondrial genomes compose this multiprotein complex, its assembly being a highly complex process involving at least 15 additional nuclear encoded assembly factors. Complex I deficiency is a mitochondrial disorder usually associated with early-onset severe multisystem disorders characterized by highly variable clinical manifestations. Flavin adenine dinucleotide (FAD)-dependent oxidoreductase domain-containing protein 1 (FOXRED1) is a complex I assembly factor. To date, only five patients with mitochondrial complex I deficiency due to mutations in FOXRED1 have been characterized. Here, we describe a child with ataxia, epilepsy and psychomotor developmental delay carrying two heterozygous FOXRED1 variants, c.920G>A (p.Gly307Glu) and c.733+1G>A. We demonstrate the molecular mechanism supporting the pathogenicity of the FOXRED1 variants, showing a clear deficiency of complex I activity. The reduction in the steady-state level of complex I holoenzyme in patient fibroblasts, confirmed the pathogenicity of the variants and showed the molecular mechanism behind their pathogenicity. A comparison of the clinical presentation of the index case with the previously described cases allowed deepening our knowledge about the clinical variability associated with FOXRED1 defects.

The developmental expression of taxon-specific crystallins in the duck lens

The three crystallins, alpha B-crystallin, tau-crystallin/alpha-enolase and epsilon-crystallin/lactate dehydrogenase B are all stress induced proteins and may thus share common regulatory elements. However, no evidence was found for coordinate expression of these three genes during duck lens development. The alpha B- and alpha-enolase/tau-crystallin mRNAs accumulate with similar kinetics between day 12 and day 24 of embryonic development but differ in their epithelial versus fibre cell location; the LDH-B/epsilon-crystallin transcript shares its preferential location in the fibre cell with alpha B-crystallin but differs in its developmental pattern of expression. The accumulation of LDH-B/epsilon-crystallin mRNA in heart and lens followed a similar developmental pattern. In contrast, the alpha-enolase/tau-crystallin mRNA level in heart decreases while the level in lens rises. The LDH-B gene is used as a crystallin gene in duck but not in chicken. This species-specific difference may correlate with the difference in LDH-B activity between various chicken and duck tissues: the retina and pancreas in duck have significantly higher LDH-B activity than in chick, while heart, muscle, stomach, liver, intestine and kidney all have much higher LDH-B activity in chicken than in duck.

Relocalization of alpha B-crystallin by heat shock in ovarian carcinoma cells

alpha B-Crystallin, a major lens protein, is present in clearly detectable amounts in cultured ovarian carcinoma cells. After heat-shock treatment of these cells at 45 degrees C alpha B-crystallin relocalizes from the detergent-soluble, cytosolic fraction to the non-ionic detergent-insoluble nuclear/cytoskeletal fraction. Colchicine treatment of the cells, although giving rise to a vimentin collapse on the nucleus, does not result in redistribution of alpha B-cyrstallin. When this colchicine treatment is followed by heat shock, alpha B-crystallin relocalizes again to the insoluble fraction, indicating that this relocalization is independent of the collapse of the vimentin network.