Hypertrophic cardiomyopathy with cardiac rupture and tamponade caused by congenital disorder of glycosylation type Ia

Metabolic Cardiomyopathies and Cardiac Defects in Inherited Disorders of Carbohydrate Metabolism: A Systematic Review

Heart failure (HF) is a progressive chronic disease that remains a primary cause of death worldwide, affecting over 64 million patients. HF can be caused by cardiomyopathies and congenital cardiac defects with monogenic etiology. The number of genes and monogenic disorders linked to development of cardiac defects is constantly growing and includes inherited metabolic disorders (IMDs). Several IMDs affecting various metabolic pathways have been reported presenting cardiomyopathies and cardiac defects. Considering the pivotal role of sugar metabolism in cardiac tissue, including energy production, nucleic acid synthesis and glycosylation, it is not surprising that an increasing number of IMDs linked to carbohydrate metabolism are described with cardiac manifestations. In this systematic review, we offer a comprehensive overview of IMDs linked to carbohydrate metabolism presenting that present with cardiomyopathies, arrhythmogenic disorders and/or structural cardiac defects. We identified 58 IMDs presenting with cardiac complications: 3 defects of sugar/sugar-linked transporters (GLUT3, GLUT10, THTR1); 2 disorders of the pentose phosphate pathway (G6PDH, TALDO); 9 diseases of glycogen metabolism (GAA, GBE1, GDE, GYG1, GYS1, LAMP2, RBCK1, PRKAG2, G6PT1); 29 congenital disorders of glycosylation (ALG3, ALG6, ALG9, ALG12, ATP6V1A, ATP6V1E1, B3GALTL, B3GAT3, COG1, COG7, DOLK, DPM3, FKRP, FKTN, GMPPB, MPDU1, NPL, PGM1, PIGA, PIGL, PIGN, PIGO, PIGT, PIGV, PMM2, POMT1, POMT2, SRD5A3, XYLT2); 15 carbohydrate-linked lysosomal storage diseases (CTSA, GBA1, GLA, GLB1, HEXB, IDUA, IDS, SGSH, NAGLU, HGSNAT, GNS, GALNS, ARSB, GUSB, ARSK). With this systematic review we aim to raise awareness about the cardiac presentations in carbohydrate-linked IMDs and draw attention to carbohydrate-linked pathogenic mechanisms that may underlie cardiac complications.

Hyperinsulinism May Be Underreported in Hypoglycemic Patients with Phosphomannomutase 2 Deficiency

Objective

Phosphomannomutase 2 deficiency (PMM2-CDG) is a disorder of protein N-glycosylation with a wide clinical spectrum. Hypoglycemia is rarely reported in PMM2-CDG. In this study, we evaluated cause, treatment options and outcomes in cases with hypoglycemia in the course of PMM2-CDG.

Methods

Clinical records of patients followed with PMM2-CDG within the last two decades were reviewed. Medical data of patients with hypoglycemia were evaluated in more detail. Demographic and clinical findings, organ involvement and laboratory investigations at time of hypoglycemia were recorded. Time of first attack of hypoglycemia, cause, treatment modalities, duration of hypoglycemia (permanent/transient), and duration of treatment, as well as outcome were also recorded. Other published cases with PMM2-CDG and hypoglycemia are also reviewed in order to elucidate characteristics as well as pathophysiology of hypoglycemia.

Results

Nine patients with PMM2-CDG were reviewed, and hypoglycemia was present in three cases. All three had hyperinsulinism as the cause of hypoglycemia. In the first two cases reported here, serum insulin level concurrent with hypoglycemic episodes was elevated, and glucose response was exaggerated during glucagon test, favoring hyperinsulinism. However, in the third case, the serum insulin level at time of hypoglycemia was not so high but hypoglycemia responded well to diazoxide. Hyperinsulinism was permanent in two of these three cases. No genotype-phenotype correlation was observed with respect to hyperinsulinism.

Conclusion

The main cause of hypoglycemia in PMM2-CDG appears to be hyperinsulinism. Although insulin levels at the time of hypoglycemia may not be very high, hypoglycemia in patients with PMM2 responds well to diazoxide.

Vascular ring anomaly in a patient with phosphomannomutase 2 deficiency: A case report and review of the literature

BACKGROUND

Congenital disorders of glycosylation (CDG) are a group of metabolic disorders well known to be associated with developmental delay and central nervous system anomalies. The most common CDG is caused by pathogenic variants in the phosphomannomutase 2 gene (PMM2), which impairs one of the first steps of N-glycosylation and affects multiple organ systems. Cardiac involvement can include pericardial effusion, cardiomyopathy, and arrhythmia, while an association with cardiovascular congenital anomalies is not well studied.

CASE SUMMARY

We report a 6-year-old individual who initially presented with inverted nipples, developmental delay, and failure to thrive at 3 months of age. At 4 months, due to feeding problems, swallowing exam and echocardiography were performed which revealed a vascular ring anomaly based on a right aortic arch and aberrant left subclavian artery. Subsequent whole exome gene sequencing revealed two pathogenic PMM2-CDG variants (E139K/R141H) and no known pathogenic mutations related to congenital heart defect (CHD).

DISCUSSION

This is the first report of vascular ring anomaly in a patient with PMM2-CDG. We conducted a literature review of PMM2-CDG patients with reported CHD. Of the 14 patients with PMM2-CDG and cardiac malformation, the most common CHD's were tetralogy of Fallot, patent ductus arteriosus, and truncus arteriosus. The potential important link between CDG and CHD is stressed and discussed. Furthermore, the importance of multidisciplinary care for CDG patients including early referral to pediatric cardiologists is highlighted.

Hypoglycemia in CDG patients due to PMM2 mutations: Follow up on hyperinsulinemic patients

BACKGROUND

Phosphomannomutase 2 deficiency (PMM2-CDG) is the most common congenital disorder of glycosylation (CDG). Hypoglycemia has been reported in various CDG including PMM2-CDG. The frequency and etiology of hypoglycemia in PMM2-CDG are not well studied.

METHODS

We conducted a systematic review of the literature on genetically and/or biochemically confirmed PMM2-CDG patients who developed hypoglycemia. Prospective follow-up information on the patients who received diazoxide therapy was collected and evaluated.

RESULTS

A total of 165 peer-reviewed articles reporting on 933 PMM2-CDG patients were assessed. Hypoglycemia was specifically mentioned only in 23 of these patients (2.5%). Hyperinsulinism was identified in 10 patients (43% of all hypoglycemic patients). Among these 10 patients, seven were successfully treated with diazoxide. However, most patients remained on therapy longer than a year to stay free of hypoglycemia.

CONCLUSION

Hypoglycemia is a rarely reported finding in patients with PMM2-CDG. Diazoxide-responsive hyperinsulinism was found to have a good prognosis on medication in our PMM2-CDG patients with hypoglycemia. No genotype-phenotype correlation was observed with respect to hyperinsulinism. A prospective study should be undertaken to explore the hypothesis that hypoglycemia is underdiagnosed in PMM2-CDG and to evaluate whether hyperinsulinism is always associated with hypoglycemia.

International clinical guidelines for the management of phosphomannomutase 2-congenital disorders of glycosylation: Diagnosis, treatment and follow up

Phosphomannomutase 2 (PMM2-CDG) is the most common congenital disorder of N-glycosylation and is caused by a deficient PMM2 activity. The clinical presentation and the onset of PMM2-CDG vary among affected individuals ranging from a severe antenatal presentation with multisystem involvement to mild adulthood presentation limited to minor neurological involvement. Management of affected patients requires a multidisciplinary approach. In this article, a systematic review of the literature on PMM2-CDG was conducted by a group of international experts in different aspects of CDG. Our managment guidelines were initiated based on the available evidence-based data and experts' opinions. This guideline mainly addresses the clinical evaluation of each system/organ involved in PMM2-CDG, and the recommended management approach. It is the first systematic review of current practices in PMM2-CDG and the first guidelines aiming at establishing a practical approach to the recognition, diagnosis and management of PMM2-CDG patients.

Recognizable phenotypes in CDG

Pattern recognition, using a group of characteristic, or discriminating features, is a powerful tool in metabolic diagnostic. A classic example of this approach is used in biochemical analysis of urine organic acid analysis, where the reporting depends more on the correlation of pertinent positive and negative findings, rather than on the absolute values of specific markers. Similar uses of pattern recognition in the field of biochemical genetics include the interpretation of data obtained by metabolomics, like glycomics, where a recognizable pattern or the presence of a specific glycan sub-fraction can lead to the direct diagnosis of certain types of congenital disorders of glycosylation. Another indispensable tool is the use of clinical pattern recognition-or syndromology-relying on careful phenotyping. While genomics might uncover variants not essential in the final clinical expression of disease, and metabolomics could point to a mixture of primary but also secondary changes in biochemical pathways, phenomics describes the clinically relevant manifestations and the full expression of the disease. In the current review we apply phenomics to the field of congenital disorders of glycosylation, focusing on recognizable differentiating findings in glycosylation disorders, characteristic dysmorphic features and malformations in PMM2-CDG, and overlapping patterns among the currently known glycosylation disorders based on their pathophysiological basis.

Cardiac complications of congenital disorders of glycosylation (CDG): a systematic review of the literature

Congenital disorders of glycosylation (CDG) are inborn errors of metabolism due to protein and lipid hypoglycosylation. This rapidly growing family of genetic diseases comprises 103 CDG types, with a broad phenotypic diversity ranging from mild to severe poly-organ -system dysfunction. This literature review summarizes cardiac involvement, reported in 20% of CDG. CDG with cardiac involvement were divided according to the associated type of glycosylation: N-glycosylation, O-glycosylation, dolichol synthesis, glycosylphosphatidylinositol (GPI)-anchor biosynthesis, COG complex, V-ATPase complex, and other glycosylation pathways. The aim of this review was to document and interpret the incidence of heart disease in CDG patients. Heart disorders were grouped into cardiomyopathies, structural defects, and arrhythmogenic disorders. This work may contribute to improved early management of cardiac complications in CDG.

Infant with cardiomyopathy: When to suspect inborn errors of metabolism?

Inborn errors of metabolism are identified in 5%-26% of infants and children with cardiomyopathy. Although fatty acid oxidation disorders, lysosomal and glycogen storage disorders and organic acidurias are well-known to be associated with cardiomyopathies, emerging reports suggest that mitochondrial dysfunction and congenital disorders of glycosylation may also account for a proportion of cardiomyopathies. This review article clarifies when primary care physicians and cardiologists should suspect inborn errors of metabolism in a patient with cardiomyopathy, and refer the patient to a metabolic specialist for a further metabolic work up, with specific discussions of “red flags” which should prompt additional evaluation.