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Mutations in the X-linked ATP6AP2 cause a glycosylation disorder with autophagic defects

Publication . Rujano, M.; Cannata Serio, M.; Panasyuk, G.; Péanne, R.; Reunert, J.; Rymen, D.; Hauser, V.; Park, J.; Freisinger, P.; Souche, E.; Guida, M.; Maier, E.; Wada, Y.; Jäger, S.; Krogan, N.; Kretz, O.; Nobre, S.; Garcia, P.; Quelhas, D.; Bird, T.; Raskind, W.; Schwake, M.; Duvet, S.; Foulquier, F.; Matthijs, G.; Marquardt, T.; Simons, M.

The biogenesis of the multi-subunit vacuolar-type H+-ATPase (V-ATPase) is initiated in the endoplasmic reticulum with the assembly of the proton pore V0, which is controlled by a group of assembly factors. Here, we identify two hemizygous missense mutations in the extracellular domain of the accessory V-ATPase subunit ATP6AP2 (also known as the [pro]renin receptor) responsible for a glycosylation disorder with liver disease, immunodeficiency, cutis laxa, and psychomotor impairment. We show that ATP6AP2 deficiency in the mouse liver caused hypoglycosylation of serum proteins and autophagy defects. The introduction of one of the missense mutations into Drosophila led to reduced survival and altered lipid metabolism. We further demonstrate that in the liver-like fat body, the autophagic dysregulation was associated with defects in lysosomal acidification and mammalian target of rapamycin (mTOR) signaling. Finally, both ATP6AP2 mutations impaired protein stability and the interaction with ATP6AP1, a member of the V0 assembly complex. Collectively, our data suggest that the missense mutations in ATP6AP2 lead to impaired V-ATPase assembly and subsequent defects in glycosylation and autophagy.

2017-12-04Journal article

Open access

Classical fragile-X phenotype in a female infant disclosed by comprehensive genomic studies

Publication . Jorge, P.; Garcia, E.; Gonçalves, A.; Marques, I.; Maia, N.; Rodrigues, B.; Santos, H.; Fonseca, J.; Soares, G.; Correia, C.; Reis-Lima, M.; Cirigliano, V.; Santos, R.

BACKGROUND: We describe a female infant with Fragile-X syndrome, with a fully expanded FMR1 allele and preferential inactivation of the homologous X-chromosome carrying a de novo deletion. This unusual and rare case demonstrates the importance of a detailed genomic approach, the absence of which could be misguiding, and calls for reflection on the current clinical and diagnostic workup for developmental disabilities. CASE PRESENTATION: We present a female infant, referred for genetic testing due to psychomotor developmental delay without specific dysmorphic features or relevant family history. FMR1 mutation screening revealed a methylated full mutation and a normal but inactive FMR1 allele, which led to further investigation. Complete skewing of X-chromosome inactivation towards the paternally-inherited normal-sized FMR1 allele was found. No pathogenic variants were identified in the XIST promoter. Microarray analysis revealed a 439 kb deletion at Xq28, in a region known to be associated with extreme skewing of X-chromosome inactivation. CONCLUSIONS: Overall results enable us to conclude that the developmental delay is the cumulative result of a methylated FMR1 full mutation on the active X-chromosome and the inactivation of the other homologue carrying the de novo 439 kb deletion. Our findings should be taken into consideration in future guidelines for the diagnostic workup on the diagnosis of intellectual disabilities, particularly in female infant cases.

2018-05-10Journal article

Open access