Expanding the phenotypic spectrum of ARCN1-related syndrome

The Therapeutic Future for Congenital Disorders of Glycosylation

The past decade, novel treatment options for congenital disorders of glycosylation (CDG) have advanced rapidly. Innovative therapies, targeting both the root cause, the affected metabolic pathways, and resulting manifestations, have transitioned from the research stage to practical applications. However, with novel therapeutic abilities, novel challenges await, specifically when it concerns the large number of clinical trials that need to be performed in order to treat all 190 genetic defects that cause CDG known to date. The present paper aims to provide an overview of how the CDG field can keep advancing its therapeutic strategies over the coming years with these challenges in mind. We focus on three important pillars that may shape the future of CDG: the use of disease models, clinical trial readiness, and the possibility to make individualized treatments scalable to the entire CDG cohort.

Disease-Associated Factors at the Endoplasmic Reticulum-Golgi Interface

The endoplasmic reticulum (ER)-Golgi interface is essential for directing the transport of proteins synthesized in the ER to the Golgi apparatus via the ER-Golgi intermediate compartment, as well as for recycling proteins back to the ER. This transport is facilitated by various components, including COPI and COPII coat protein complexes and the transport protein particle complex. Recently, the ER-Golgi transport pathway has gained attention due to emerging evidence of nonvesicular transport mechanisms and the regulation of trafficking through liquid-liquid phase separation. Numerous diseases have been linked to mutations in proteins localized at the ER-Golgi interface, highlighting the need for comprehensive analysis of these conditions. This review examines the disease phenotypes associated with dysfunctional ER-Golgi transport factors and explores their cellular effects, providing insights into potential therapeutic strategies.

A novel ARCN1 splice-site variant in a Chinese girl with central precocious puberty, intrauterine growth restriction, microcephaly, and microretrognathia

The ARCN1 gene encodes the delta subunit of the coatomer protein complex I (COPI), which is essential for mediating protein transport from the Golgi complex to the endoplasmic reticulum. Variants in ARCN1 are associated with clinical features such as microcephaly, microretrognathia, intrauterine growth restriction, short rhizomelic stature, and developmental delays. We present a case of a patient exhibiting intrauterine growth restriction, preterm birth, microcephaly, micrognathia, and central precocious puberty. Whole-exome sequencing identified a novel splice-site variant, NM_001655.5: c.1241 + 1G > A, in the ARCN1 gene. To our knowledge, this is the first documented case of ARCN1-related syndrome associated with central precocious puberty, contributing to the understanding of the disease phenotype.

SEC31A may be associated with pituitary hormone deficiency and gonadal dysgenesis

PURPOSE

Disorders/differences of sex development (DSD) result from variants in many different human genes but, frequently, have no detectable molecular cause.

METHODS

Detailed clinical and genetic phenotyping was conducted on a family with three children. A Sec31a animal model and functional studies were used to investigate the significance of the findings.

RESULTS

By trio whole-exome DNA sequencing we detected a heterozygous de novo nonsense SEC31A variant, in three children of healthy non-consanguineous parents. The children had different combinations of disorders that included complete gonadal dysgenesis and multiple pituitary hormone deficiency. SEC31A encodes a component of the COPII coat protein complex, necessary for intracellular anterograde vesicle-mediated transport between the endoplasmic reticulum (ER) and Golgi. CRISPR-Cas9 targeted knockout of the orthologous Sec31a gene region resulted in early embryonic lethality in homozygous mice. mRNA expression of ER-stress genes ATF4 and CHOP was increased in the children, suggesting defective protein transport. The pLI score of the gene, from gnomAD data, is 0.02.

CONCLUSIONS

SEC31A might underlie a previously unrecognised clinical syndrome comprising gonadal dysgenesis, multiple pituitary hormone deficiencies, dysmorphic features and developmental delay. However, a variant that remains undetected, in a different gene, may alternatively be causal in this family.

The Radiological and Histological Phenotype of Skeletal Abnormalities in Fetal ARCN1-Related Syndrome

Mutations in ARCN1 give rise to a syndromic disorder with rhizomelic short stature with microretrognathia and developmental delay. ARCN1 encodes the delta subunit of the coat protein I complex, which is required for intracellular trafficking of collagen 1 and which may also be involved in the endoplasmic reticulum (ER) stress response. In this paper we describe for the first time the skeletal histological abnormalities in an 18-week-old fetus with an ARCN1 mutation, and we suggest that the skeletal phenotype in ARCN1-related syndrome has more resemblance with ER stress than with a defect in collagen 1 metabolism.

The best of both worlds: Blending cutting-edge research with clinical processes for a productive exome clinic

Genomic medicine has been transformed by next-generation sequencing (NGS), inclusive of exome sequencing (ES) and genome sequencing (GS). Currently, ES is offered widely in clinical settings, with a less prevalent alternative model consisting of hybrid programs that incorporate research ES along with clinical patient workflows. We were among the earliest to implement a hybrid ES clinic, have provided diagnoses to 45% of probands, and have identified several novel candidate genes. Our program is enabled by a cost-effective investment by the health system and is unique in encompassing all the processes that have been variably included in other hybrid/clinical programs. These include careful patient selection, utilization of a phenotype-agnostic bioinformatics pipeline followed by manual curation of variants and phenotype integration by clinicians, close collaborations between the clinicians and the bioinformatician, pursuit of interesting variants, communication of results to patients in categories that are predicated upon the certainty of a diagnosis, and tracking changes in results over time and the underlying mechanisms for such changes. Due to its effectiveness, scalability to GS and its resource efficiency, specific elements of our paradigm can be incorporated into existing clinical settings, or the entire hybrid model can be implemented within health systems that have genomic medicine programs, to provide NGS in a scientifically rigorous, yet pragmatic setting.