Prenatal presentation of a rare genetic disorder: a clinical, autopsy and molecular correlation

Walker Warburg syndrome (WWS) lies at the severe end of the spectrum of the congenital muscular dystrophies. WWS is a congenital disorder of the O-glycosylation that disrupts in the post-translation modification of dystroglycan proteins. WWS is characterized by the involvement of the central nervous system and rarely by multisystem involvement. Next-generation sequencing discovered that multiple genes are associated with this disorder. FKTN is the rarest cause of WWS. We describe a clinical-autopsy report of a molecularly- confirmed WWS case presenting with ventriculomegaly, agenesis of the corpus callosum with a novel phenotype of Dandy-Walker malformation and unilateral multi-cystic kidney. The whole-exome sequencing confirmed a homozygous variant (c.411C>A) in the FKTN gene with a premature termination codon. This case emphasizes the importance of detailed postnatal phenotyping through an autopsy in any pregnancy with antenatally identified malformations. Obstetricians, pediatricians as well as fetal medicine experts need to counsel the parents and focus on preserving the appropriate sample for genetic testing. WWS, though rare deserves testing especially in the presence of positive family history. Dandy-Walker malformation is a novel feature and expands the phenotypic spectrum.

The yeast protein Gdt1p transports Mn2+ ions and thereby regulates manganese homeostasis in the Golgi

The uncharacterized protein family 0016 (UPF0016) is a family of secondary ion transporters implicated in calcium homeostasis and some diseases. More precisely, genetic variants of the human UPF0016 ortholog transmembrane protein 165 (TMEM165) have been linked to congenital disorders of glycosylation (CDG). The Saccharomyces cerevisiae ortholog Gdt1p has been shown to be involved in calcium homeostasis and protein glycosylation. Moreover, plant and bacterial UPF0016 members appear to have putative roles in Mn²⁺ homeostasis. Here, we produced the yeast UPF0016 member Gdt1p in the bacterial host Lactococcus lactis Using Mn²⁺-induced quenching of Fura-2-emitted fluorescence, we observed that Gdt1p mediates Mn²⁺ influx, in addition to its previously reported regulation of Ca²⁺ influx. The estimated K_m values of Gdt1p of 15.6 ± 2.6 μm for Ca²⁺ and 83.2 ± 9.8 μm for Mn²⁺ indicated that Gdt1p has a higher affinity for Ca²⁺ than for Mn²⁺ In yeast cells, we found that Gdt1p is involved in the resistance to high Mn²⁺ concentration and controls total Mn²⁺ stores. Lastly, we demonstrated that GDT1 deletion affects the activity of the yeast Mn²⁺-dependent Sod2p superoxide dismutase, most likely by modulating cytosolic Mn²⁺ concentrations. Taken together, we obtained first evidence that Gdt1p from yeast directly transports manganese, which strongly reinforces the suggested link between the UPF0016 family and Mn²⁺ homeostasis and provides new insights into the molecular causes of human TMEM165-associated CDGs. Our results also shed light on how yeast cells may regulate Golgi intraluminal concentrations of manganese, a key cofactor of many enzymes involved in protein glycosylation.