Biallelic variants in NADH (nicotinamide adenine dinucleotide (NAD) + hydrogen (H))-ubiquinone oxidoreductase 1 alpha subcomplex 13 have been linked to mitochondrial complex I deficiency, nuclear type 28, based on three affected individuals from two families. With only two families reported, the clinical and molecular spectrum of NADH-ubiquinone oxidoreductase 1 alpha subcomplex 13-related diseases remains unclear. We report 10 additional affected individuals from nine independent families, identifying four missense variants (including recurrent c.170G > A) and three ultra-rare or novel predicted loss-of-function biallelic variants. Updated clinical-radiological data from previously reported families and a literature review compiling clinical features of all reported patients with isolated complex I deficiency caused by 43 genes encoding complex I subunits and assembly factors are also provided. Our cohort (mean age 7.8 +/- 5.4 years; range 2.5-18) predominantly presented a moderate-to-severe neurodevelopmental syndrome with oculomotor abnormalities (84%), spasticity/hypertonia (83%), hypotonia (69%), cerebellar ataxia (66%), movement disorders (58%) and epilepsy (46%). Neuroimaging revealed bilateral symmetric T2 hyperintense substantia nigra lesions (91.6%) and optic nerve atrophy (66.6%). Protein modeling suggests missense variants destabilize a critical junction between the hydrophilic and membrane arms of complex I. Fibroblasts from two patients showed reduced complex I activity and compensatory complex IV activity increase. This study characterizes NADH-ubiquinone oxidoreductase 1 alpha subcomplex 13-related disease in 13 individuals, highlighting genotype-phenotype correlations.

Developmental and epileptic encephalopathies (DEEs) feature altered brain development, developmental delay and seizures, with seizures exacerbating developmental delay. Here we identify a cohort with biallelic variants in DENND5A, encoding a membrane trafficking protein, and develop animal models with phenotypes like the human syndrome. We demonstrate that DENND5A interacts with Pals1/MUPP1, components of the Crumbs apical polarity complex required for symmetrical division of neural progenitor cells. Human induced pluripotent stem cells lacking DENND5A fail to undergo symmetric cell division with an inherent propensity to differentiate into neurons. These phenotypes result from misalignment of the mitotic spindle in apical neural progenitors. Cells lacking DENND5A orient away from the proliferative apical domain surrounding the ventricles, biasing daughter cells towards a more fate-committed state, ultimately shortening the period of neurogenesis. This study provides a mechanism for DENND5A-related DEE that may be generalizable to other developmental conditions and provides variant-specific clinical information for physicians and families. Developmental and epileptic encephalopathies are devastating neurological disorders. Here, the authors establish a cohort of patients with variants in the gene DENND5A and use human stem cells to discover a disease mechanism involving altered cell division.

Abstract Introduction We investigated the frequency, neuropathology, and phenotypic characteristics of spastic paraplegia (SP) that precedes dementia in presenilin 1 (PSEN1) related familial Alzheimer's disease (AD). Methods We performed whole exome sequencing (WES) in 60 probands with hereditary spastic paraplegia (HSP) phenotype that was negative for variants in known HSP‐related genes. Where PSEN1 mutation was identified, brain biopsy was performed. We investigated the link between HSP and AD with PSEN1 in silico pathway analysis and measured in vivo the stability of PSEN1 mutant γ‐secretase. Results We identified a PSEN1 variant (p.Thr291Pro) in an individual presenting with pure SP at 30 years of age. Three years later, SP was associated with severe, fast cognitive decline and amyloid deposition with diffuse cortical plaques on brain biopsy. Biochemical analysis of p.Thr291Pro PSEN1 revealed that although the mutation does not alter active γ‐secretase reconstitution, it destabilizes γ‐secretase‐amyloid precursor protein (APP)/amyloid beta (Aβn) interactions during proteolysis, enhancing the production of longer Aβ peptides. We then extended our analysis to all 226 PSEN1 pathogenic variants reported and show that 7.5% were associated with pure SP onset followed by cognitive decline later in the disease. We found that PSEN1 cases manifesting initially as SP have a later age of onset, are associated with mutations located beyond codon 200, and showed larger diffuse, cored plaques, amyloid‐ring arteries, and severe CAA. Discussion We show that pure SP can precede dementia onset in PSEN1‐related familial AD. We recommend PSEN1 genetic testing in patients presenting with SP with no variants in known HSP‐related genes, particularly when associated with a family history of cognitive decline.

We would like to reply to Neuray et al. who report a series of five new patients from four unrelated families with bi-allelic mutations of GRN. Their work nicely completes the few existing reports of similar cases, and refers to our recent publication describing six homozygous GRN pathogenic variant carriers with divergent phenotypes and ages at onset (Huin et al., 2020). In summary, the Letter from Neuray et al., reports valuable findings that lead to better define CLN11 due to bi-allelic GRN pathogenic variants. Despite the small sample number that does not allow statistical analysis, the authors underlined the occurrence of cognitive deterioration and epilepsy. Further study of the CLN11 families with functional brain imaging and neuropsychological examinations may be highly informative for the understanding and the clinical characterization of this rare disease.