Nanophthalmos patient with a THR518MET mutation in MYRF, a case report

Myelin regulatory factor ( Myrf ) is a critical early regulator of retinal pigment epithelial development

Myelin regulatory factor (Myrf) is a critical transcription factor in early retinal and retinal pigment epithelial development, and human variants in MYRF are a cause for nanophthalmos. Single cell RNA sequencing (scRNAseq) was performed on Myrf conditional knockout mice ( Rx>Cre Myrf fl/fl ) at 3 developmental timepoints. Myrf was expressed specifically in the RPE, and expression was abrogated in Rx>Cre Myrf fl/fl eyes. scRNAseq analysis revealed a loss of RPE cells at all timepoints resulting from cell death. GO-term analysis in the RPE revealed downregulation of melanogenesis and anatomic structure morphogenesis pathways, which were supported by electron microscopy and histologic analysis. Novel structural target genes including Ermn and Upk3b , along with macular degeneration and inherited retinal disease genes were identified as downregulated, and a strong upregulation of TGFß/BMP signaling and effectors was observed. Regulon analysis placed Myrf downstream of Pax6 and Mitf and upstream of Sox10 in RPE differentiation. Together, these results suggest a strong role for Myrf in the RPE maturation by regulating melanogenesis, cell survival, and cell structure, in part acting through suppression of TGFß signaling and activation of Sox10 .

SUMMARY STATEMENT

Myrf regulates RPE development, melanogenesis, and is important for cell structure and survival, in part through regulation of Ermn , Upk3b and Sox10, and BMP/TGFb signaling.

MYRF: A unique transmembrane transcription factor- from proteolytic self-processing to its multifaceted roles in animal development

The Myelin Regulator Factor (MYRF) is a master regulator governing myelin formation and maintenance in the central nervous system. The conservation of MYRF across metazoans and its broad tissue expression suggest it has functions extending beyond the well-established role in myelination. Loss of MYRF results in developmental lethality in both invertebrates and vertebrates, and MYRF haploinsufficiency in humans causes MYRF-related Cardiac Urogenital Syndrome, underscoring its importance in animal development; however, these mechanisms are largely unexplored. MYRF, an unconventional transcription factor, begins embedded in the membrane and undergoes intramolecular chaperone mediated trimerization, which triggers self-cleavage, allowing its N-terminal segment with an Ig-fold DNA-binding domain to enter the nucleus for transcriptional regulation. Recent research suggests developmental regulation of cleavage, yet the mechanisms remain enigmatic. While some parts of MYRF's structure have been elucidated, others remain obscure, leaving questions about how these motifs are linked to its intricate processing and function.

Diverse clinical manifestations and intrafamilial variability due to an inherited recurrent MYRF variant

MYRF monoallelic variants have been described in syndromic forms characterized by cardiac-urogenital syndrome and isolated nanophthalmos with/without minor systemic manifestations. We describe a large family with a paternally inherited pathogenic variant in MYRF that manifested as congenital diaphragmatic hernia (CDH), cardiac and urogenital abnormalities, and/or nanophthalmos with significant intrafamilial variability.

Case Report: De novo variant in myelin regulatory factor in a Chinese child with 46,XY disorder/difference of sex development, cardiac and urogenital anomalies, and short stature

The myelin regulatory factor (MYRF; MIM# 608329) gene was first identified as a critical transcription factor involved in oligodendrocyte differentiation and central nervous system myelination. With the recent development of exome sequencing, pathogenic variants of MYRF had been considered as the cause of cardiac-urogenital syndrome (CUGS), 46,XY and 46,XX disorders/differences of sex development (DSDs), and nanophthalmos. Herein, we described a 4-year-7-month-old "girl" with ventricular septal defect, atrial septal defect, patent ductus arteriosus, severe pulmonary hypertension, moderate-to-severe tricuspid regurgitation, enlarged coronary sinus, left superior vena cava, and right lung hypoplasia at birth. Later, the patient developed short stature and amblyopia. Further examination revealed a karyotype 46,XY and visible uterus, whereas the presence of gonads were not explored. Laparoscopy revealed dysplasia of testicular gonad. Whole-exome sequencing (WES) was performed and a de novo heterozygous mutation in MYRF was identified, known as c.2817G > A/p. W939* (NM_001127392.3). Therefore, this case report presented multiple clinical manifestations with syndromic symptoms of CUGS, 46,XY DSD, and ocular symptoms. These new data expanded the phenotype of the MYRF variant and may benefit to characterize the phenotypes caused by the variants of this gene.

Evaluation of MYRF as a candidate gene for primary angle closure glaucoma

PURPOSE

Primary angle-closure glaucoma (PACG) is a leading cause of blindness. Despite tremendous human effort and financial input, no definitive causative gene has been identified either through genome-wide association or Mendelian family studies. In the current study, novel candidate genes for PACG were investigated by studying the variants of nanophthalmos-associated genes.

METHODS

A case-control study was conducted that included 45 PACG patients and 12 normal controls with short axial length (AL, less than 23.5 mm but more than 20.5 mm). Whole-exome sequencing (WES) was performed to screen the variants in previously identified nanophthalmos-associated genes, as well as other risk genes.

RESULTS

The age range of the 45 PACG patients was 24 to 80 years, with an average AL of 21.87±0.65 mm (range: 20.54-23.45 mm) in the right eye and 21.89±0.64 mm (range 20.60-23.23 mm) in the left eye. Four novel myelin regulatory factor (MYRF) gene missense variants (p.G117S, p.H1057R, p.H230R, and p.R316C) were identified in four out of the 45 enrolled PACG patients, respectively. No MYRF or other nanophthalmos-associated gene variants were detected in the 12 normal controls.

CONCLUSIONS

An appropriate approach was adopted to investigate the genetics of PACG through nanophthalmos-associated genes. A genetic variant, MYRF, was identified in four out of 45 PACG patients, which might be a novel candidate gene for PACG.

Functional mechanisms of MYRF DNA-binding domain mutations implicated in birth defects

Myrf is a pleiotropic membrane-bound transcription factor that plays critical roles in diverse organisms, including in oligodendrocyte differentiation, embryonic development, molting, and synaptic plasticity. Upon autolytic cleavage, the Myrf N-terminal fragment enters the nucleus as a homo-trimer and functions as a transcription factor. Homo-trimerization is essential for this function because it imparts DNA-binding specificity and affinity. Recent exome sequencing studies have implicated four de novo MYRF DNA-binding domain (DBD) mutations (F387S, Q403H, G435R, and L479V) in novel syndromic birth defects involving the diaphragm, heart, and the urogenital tract. It remains unknown whether and how these four mutations alter the transcription factor function of MYRF. Here, we studied them by introducing homologous mutations to the mouse Myrf protein. We found that the four DBD mutations abolish the transcriptional activity of the Myrf N-terminal fragment by interfering with its homo-trimerization ability by perturbing the DBD structure. Since the Myrf N-terminal fragment strictly functions as a homo-trimer, any loss-of-function mutation has the potential to act as a dominant negative. We observed that one copy of Myrf-F387S, Myrf-Q403H, or Myrf-L479V, but not Myrf-G435R, was tolerated by the Myrf N-terminal homo-trimer for structural and functional integrity. These data suggest that F387S, Q403H, and L479V cause birth defects by haploinsufficiency, while G435R does so via dominant negative functionality.