Infantile SOD1 deficiency syndrome caused by a homozygous SOD1 variant with absence of enzyme activity.

Pathogenic variants in SOD1, encoding superoxide dismutase 1, are responsible for about 20% of all familial amyotrophic lateral sclerosis cases, through a gain-of-function mechanism. Recently, two reports showed that a specific homozygous SOD1 loss-of-function variant is associated with an infantile progressive motor-neurological syndrome. Exome sequencing followed by molecular studies, including cDNA analysis, SOD1 protein levels and enzymatic activity, and plasma neurofilament light chain levels, were undertaken in an infant with severe global developmental delay, axial hypotonia and limb spasticity. We identified a homozygous 3-bp in-frame deletion in SOD1. cDNA analysis predicted the loss of a single valine residue from a tandem pair (p.Val119/Val120) in the wild-type protein, yet expression levels and splicing were preserved. Analysis of SOD1 activity and protein levels in erythrocyte lysates showed essentially no enzymatic activity and undetectable SOD1 protein in the child, whereas the parents had ∼50% protein expression and activity relative to controls. Neurofilament light chain levels in plasma were elevated, implying ongoing axonal injury and neurodegeneration. Thus, we provide confirmatory evidence of a second biallelic variant in an infant with a severe neurological syndrome and suggest that the in-frame deletion causes instability and subsequent degeneration of SOD1. We highlight the importance of the valine residues at positions V119-120, and suggest possible implications for future therapeutics research.

Adverse effects of nitroglycerin treatment on endothelial function, vascular nitrotyrosine levels and cGMP-dependent protein kinase activity in hyperlipidemic Watanabe rabbits.

OBJECTIVE: With the present studies we sought to determine how treatment with nitroglycerin (NTG) affects endothelial function, oxidative stress and nitric oxide (NO)-downstream signaling in Watanabe heritable hyperlipidemic rabbits (WHHL). BACKGROUND: In vitro experiments have demonstrated potent antiatherosclerotic effects of NO suggesting that treatment with NO-donors such as NTG could compensate for the diminished availability of endothelial NO. Nitric oxide may, however, not only be scavenged by reaction with endothelium-derived superoxide but also form the potent oxidant and inhibitor of vascular function, peroxynitrite (ONOO(-)). METHODS: Watanabe heritable hyperlipidemic rabbits were treated for three days with NTG patches. Normolipidemic New Zealand White rabbits (NZWR) served as controls. Endothelial function was assessed ex vivo with organ chamber experiments and vascular superoxide was quantified using lucigenin (5 and 250 microM) and CLA-enhanced chemiluminescence. Vascular ONOO(-) formation was determined using nitrotyrosine antibodies. The activity of the cGMP-dependent kinase (cGK-I) was assessed by determining the phosphorylation of vasodilator-stimulated phosphoprotein VASP (P-VASP). RESULTS: Nitroglycerin treatment caused endothelial dysfunction in NZWR and WHHL, associated with an increase in superoxide and ONOO(-) production and a substantial drop in cGK-I activity. In vivo NTG-treatment decreased lipophilic antioxidants (alpha- and beta-carotene) in NZWR and WHHL. Treatment of NZWR with NTG also decreased plasma extracellular superoxide dismutase (EC-SOD)-activity. CONCLUSIONS: Nitroglycerin treatment of WHHL with exogenous NO worsens rather than improves endothelial dysfunction secondary to increased formation of superoxide and/or peroxynitrite leading to decreased cGK-I activity. The decrease in plasma levels of alpha- and beta-carotene may be at least in part due to a decrease in EC-SOD activity.