Ontogenesis of the tear drainage system requires Prickle1-driven polarized basement membrane deposition

GPC4 truncating variant associated with Keipert syndrome and lacrimal punctal agenesis

Lacrimal punctal agenesis is an extremely rare condition with an unclear genetic basis. Here, we report a 3-year-old male patient harboring a hemizygous variant in glypican 4 (GPC4), which causes Keipert syndrome, who presented with complete lacrimal punctal agenesis, distinctive craniofacial features, mild developmental delay, mild intellectual disability, and autism. The craniofacial features included a prominent forehead, epicanthus, depressed and broad nasal bridge, hypoplastic columella, midface hypoplasia, tented upper lip, and low-set ears. Proband exome sequencing identified a hemizygous variant in GPC4: NM_001448.3:c.1051C > T (p.Arg351*). The GPC4 variant was inherited from his heterozygous mother; X-inactivation followed a skewed pattern in his mother. This patient demonstrated clinical features consistent with Keipert syndrome including craniofacial features, brachydactyly, broad distal phalanx, broad first toe, and mild developmental delay; however, agenesis of the lacrimal puncta has not been reported previously in Keipert syndrome. Our findings suggest that GPC4, which encodes a heparan-sulfate proteoglycan, may play an important role in lacrimal morphogenesis. Our observations also suggest that Keipert syndrome should be considered in patients with lacrimal punctal agenesis.

Malformation of Tear Ducts Underlies the Epiphora and Precocious Eyelid Opening in Prickle 1 Mutant Mice: Genetic Implications for Tear Duct Genesis

Purpose

Obstruction of the tear drainage causes a range of ocular surface disorders. Hitherto, the genetics of tear duct development and obstruction has been scarcely explored, and related animal models are lacking. This study aims to study the potential role of the Wnt/PCP pathway mediated by Prickle 1 in tear duct development and diseases.

Methods

A severe hypomorphic Prickle 1 mutant was generated. Histology and immunohistochemistry were performed to compare wild type, Prickle 1 hypomorphic, and null mutant tear ducts. In situ hybridization was conducted to identify the signaling components in the developing tear ducts. Three-dimensional (3D) reconstruction was used to detect the human embryonic tear duct.

Results

Here, we report that a severe Prickle 1 hypomorph mouse line exhibited epiphora. This phenotype was due to the blockage of the tear drainage by incompletely formed nasolacrimal duct (NLD) and lacrimal canaliculi (LC), which also causes precocious eyelid opening. We observed a dose-dependent requirement of Prickle 1 for tear duct outgrowth. An investigation of the expression of Wnt/PCP core genes demonstrated a subset of PCP signaling components expressed in the developing tear duct. Furthermore, Prickle 1 is not required for the expression of Fgfr2/Fgf10 and p63 genes, which are associated with the NLD and LC hypoplasia in humans. Last, we showed that Prickle 1 expression in the developing tear drainage system is conserved between mice and humans.

Conclusions

The study suggests that malformed tear ducts caused by disruption of Prickle 1 underlies the epiphora and precocious eyelid opening.