Novel PMM2 missense mutation in a Chinese family with non-syndromic premature ovarian insufficiency

A comprehensive update of genotype-phenotype correlations in PMM2-CDG: insights from molecular and structural analyses

PMM2-CDG (phosphomannomutase 2-deficiency) is the most prevalent N-glycosylation disorder and results from impairments of PMM2 activity. This disease presents a large variety of pathogenic variants, which cause a wide phenotypical spectrum. This diversity, together with the low number of affected patients, raises the challenge of determining genotype-phenotype correlations in PMM2-CDG. This type of correlation could be highly significant in determining disease progression, prognosis, severity and in developing genome-personalized therapies. Structural analyses offer a valuable approach for assessing the pathogenic mechanisms within the PMM2 protein structure at a molecular level. Such an approach can reveal novel insights into the consequences of missense variants and their relationship with patients'phenotype. In this comprehensive review, we evaluate at a structural level 41 missense mutations in PMM2-CDG, examining their phenotypical characteristics and clinical severity, protein properties and interference at the enzymatic level. This work broadens the understanding of the intricate relationships between genotype and clinical manifestations of PMM2-CDG.

A novel missense variant in LAMC1 identified in a POI family by whole exome sequencing

OBJECTIVE

This study aimed to identify novel pathogenic genes and variants in a Chinese family with premature ovarian insufficiency (POI).

METHODS

A Chinese POI family was enrolled in this study. Whole exome sequencing was performed on the proband and her mother to identify the potential causative genes and variants and Sanger sequencing was used to confirm the finally identified potential pathogenic variant in the family.

RESULTS

An assessment of the family pedigree suggested that POI was inherited in an autosomal dominant manner in this family. A novel missense variant of the laminin subunit gamma-1 gene (LAMC1; NM_002293.4: c.3281A > T, p.D1094V) was finally identified in the proband and her affected mother. This variant was not found in any public databases. In silico analysis indicated the amino acid encoded at the variant site was highly conserved among mammals and associated with decreased protein stability and disrupted protein function. Its presence in the POI family was confirmed by Sanger sequencing.

CONCLUSIONS

This study firstly reported a novel missense variant of LAMC1 in a Chinese POI family, which was inherited in an autosomal dominant manner. This variant may result in the development of POI. Our results provide supporting evidence for a causative role for LAMC1 variants in POI.

Cysteine Pathogenic Variants of PMM2 Are Sensitive to Environmental Stress with Loss of Structural Stability

Congenital disorders of glycosylation (CDG) are severe metabolic disorders caused by an imbalance in the glycosylation pathway. Phosphomannomutase2 (PMM2-CDG), the most prevalent CDG, is mainly due to the disorder of PMM2. Pathogenic variants in cysteine have been found in various diseases, and cysteine residues have a potential as therapeutic targets. PMM2 harbor six cysteines; the variants Cys9Tyr (C9Y) and Cys241Ser (C241S) of PMM2 have been identified to associate with CDG, but the underlying molecular mechanisms remain uncharacterized. Here, we purified PMM2 wild type (WT), C9Y, and C241S to investigate their structural characteristics and biophysical properties by spectroscopic experiments under physiological temperature and environmental stress. Notably, the variants led to drastic changes in the protein properties and were prone to aggregate at physiological temperature. Meanwhile, PMM2 was sensitive to oxidative stress, and the cysteine pathogenic variants led to obvious aggregate formation and a higher cellular apoptosis ratio under oxidative stress. Molecular dynamic simulations indicated that the pathogenic variants changed the core domain of homomeric PMM2 and subunit binding free energy. Moreover, we tested the potential drug targeting PMM2-celastrol in cell level and explained the result by molecular docking simulation. In this study, we delineated the pathological mechanism of the cysteine substitution in PMM2, which addressed the vital role of cysteine in PMM2 and provided novel insights into prevention and treatment strategies for PMM2-CDG.

A decade of discovery: the stunning progress of premature ovarian insufficiency research in China

Premature ovarian insufficiency (POI) is one of key aspects of ovarian infertility. Due to early cession of ovarian function, POI imposes great challenges on the physiological and psychological health of women, and becomes a common cause of female infertility. In the worldwide, there has been a special outpouring of concern for about four million reproductive-aged women suffering from POI in China. Driven by advances in new technologies and efforts invested by Chinses researchers, understanding about POI has constantly been progressing over the past decade. Here, we comprehensively summarize and review the landmark development and achievements from POI studies in China spanning 2011 to 2020, which aims to provide key insights from bench to bedside.

Cystic kidney diseases associated with mutations in phosphomannomutase 2 promotor: a large spectrum of phenotypes

BACKGROUND

Co-occurrence of polycystic kidney disease and hyperinsulinemic hypoglycemia has been reported in children in a few families associated with a variant in the promotor of the PMM2 gene, at position -167 upstream of the coding sequence. PMM2 encodes phosphomannomutase 2, a key enzyme in N-glycosylation. While biallelic coding PMM2 mutations are involved in congenital disorder of glycosylation CDG1A, that particular variant in the promoter of the gene, either in the homozygous state or associated with a mutation in the coding exons of the gene, is thought to restrict the N-glycosylation defect to the kidney and the pancreas.

METHODS

Targeted exome sequencing of a panel of genes involved in monogenic kidney diseases.

RESULTS

We identified a PMM2 variant at position -167 associated with a pathogenic PMM2 variant in the coding exons in 3 families, comprising 6 cases affected with a cystic kidney disease. The spectrum of phenotypes was very broad, from extremely enlarged fetal cystic kidneys in the context of a COACH-like syndrome, to isolated cystic kidney disease with small kidneys, slowly progressing toward kidney failure in adulthood. Hypoglycemia was reported only in one case.

CONCLUSION

These data show that the PMM2 promotor variation, in trans of a PMM2 coding mutation, is associated with a wide spectrum of kidney phenotypes, and is not always associated with extra-renal symptoms. When present, extra-renal defects may include COACH-like syndrome. These data prompt screening of PMM2 in unresolved cases of fetal hyperechogenic/cystic kidneys as well as in cystic kidney disease in children and adults. Graphical Abstract.

Primary ovarian insufficiency in a female with phosphomannomutase-2 gene (PMM2) mutations for congenital disorder of glycosylation

Primary ovarian insufficiency (POI) is a highly heterogeneous condition, and its underlying causes remain to be clarified in a large fraction of patients. Congenital disorders of glycosylation (CDG) are multisystem diseases caused by mutations of a number of genes involved in N-glycosylation or O-glycosylation, and the most frequent form is PMM2-CDG (alias, CDG-Ia) resulting from biallelic mutations in PMM2 encoding phosphomannomutase-2 involved in N-glycosylation. Here, we examined a 46,XX Japanese female with syndromic POI accompanied by an undetectable level of serum anti-Müllerian hormone (AMH). Whole exome sequencing identified biallelic pathogenic mutations of PMM2 (a novel c.34G>C:p.(Asp12His) of maternal origin and a recurrent c.310C>G:p.(Leu104Val) of paternal origin) (NM_000303.3), and N-glycosylation studies detected asialotransferrin and disialotransferrin characteristic of PMM2-CDG, in addition to normally glycosylated tetrasialotransferrin. Clinical assessment showed cerebellar hypotrophy, which is a fairly characteristic and highly prevalent feature in PMM2-CDG, together with multiple non-specific features reported in PMM2-CDG such as characteristic face, intellectual disability, skeletal abnormalities, and low blood antithrombin III value. These results including the undetectable level of serum AMH, in conjunction with previously reported findings suggestive of the critical role of glycosylation in oocyte development and function, imply that PMM2-CDG almost invariably leads to POI primarily because of the defective oogenesis and/or oocyte-dependent early folliculogenesis rather than the compromised bioactivity of FSH/LH with defective glycosylation. Thus, it is recommended to examine PMM2 in patients with syndromic POI, especially in those with cerebellar ataxia/hypotrophy.