Nucleoporins build the nuclear pore complex (NPC), which, as sole gate for nuclear-cytoplasmic exchange, is of outmost importance for normal cell function. Defects in the process of nucleocytoplasmic transport or in its machinery have been frequently described in human diseases, such as cancer and neurodegenerative disorders, but only in a few cases of developmental disorders. Here we report biallelic mutations in the nucleoporin NUP88 as a novel cause of lethal fetal akinesia deformation sequence (FADS) in two families. FADS comprises a spectrum of clinically and genetically heterogeneous disorders with congenital malformations related to impaired fetal movement. We show that genetic disruption of nup88 in zebrafish results in pleiotropic developmental defects reminiscent of those seen in affected human fetuses, including locomotor defects as well as defects at neuromuscular junctions. Phenotypic alterations become visible at distinct developmental stages, both in affected human fetuses and in zebrafish, whereas early stages of development are apparently normal. The zebrafish phenotypes caused by nup88 deficiency are rescued by expressing wild-type Nup88 but not the disease-linked mutant forms of Nup88. Furthermore, using human and mouse cell lines as well as immunohistochemistry on fetal muscle tissue, we demonstrate that NUP88 depletion affects rapsyn, a key regulator of the muscle nicotinic acetylcholine receptor at the neuromuscular junction. Together, our studies provide the first characterization of NUP88 in vertebrate development, expand our understanding of the molecular events causing FADS, and suggest that variants in NUP88 should be investigated in cases of FADS.

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Fetal akinesia deformation sequence (FADS) comprises a spectrum of clinically and genetically heterogeneous disorders with congenital malformations related to impaired fetal movement. FADS often results from mutations in genes affecting the muscle nicotinic acetylcholine receptor (AChR). Here we describe mutations in NUP88 coding for the nucleoporin NUP88 as a novel cause of lethal FADS in two families. A homozygous c.1300G>T (p.D434Y) mutation in two individuals and a compound heterozygous mutation c.1525C>T (p.R509*) and c1899_1901del (p.E634del) in one individual were found. We show that genetic disruption of nup88 in zebrafish results in pleiotropic developmental defects reminiscent of those seen in affected human fetuses, including locomotor defects as well as defects at neuromuscular junctions. Loss of NUP88 coincides with aberrant levels and localization of rapsyn, a key regulator of AChR clustering. These findings expand our understanding of the molecular events causing FADS and suggest that variants in NUP88 should be investigated in cases of FADS.

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