bims-meglyc 2024-01-21 papers

Issue of 2024–01–21
five papers selected by
Silvia Radenkovic

J Genet Couns. 2024 Jan 19.

Genetic counseling for congenital disorders of glycosylation (CDG).

Tara Weixel, Lynne Wolfe, Ellen F Macnamara.

Congenital disorders of glycosylation (CDGs) are a genetically and clinically diverse group of disorders that arise as a result of defects within glycosylation synthetic pathways. CDGs are caused by pathogenic variants in many different genes in the glycosylation network. With over 160 different CDG types currently identified and a vast range of severity and presentations existing within and across those types, the road to a CDG diagnosis is often lengthy and complicated. The perils of this arduous CDG diagnostic odyssey are fraught with various genetic counseling uncertainties: (1) confusion about family planning, (2) queries about inheritance, (3) managing treatment, and (4) dealing with the uncertainty of rare diseases. Thus, the role of the genetic counselor is paramount in helping affected individuals and their families navigate these genetic counseling complexities. Case examples of common genetic counseling difficulties for CDGs are outlined, providing clinical applications of what CDG presentations, diagnostic processes, and common difficulties look like. Information on the nomenclature, incidence, prevalence, diagnostic testing, treatment, and management of CDGs are also discussed to provide a comprehensive summary of CDGs for genetic counselors, and subsequently to affected individuals and their families.

Keywords: congenital disorders of glycosylation; genetic counseling; genetic sequencing; inheritance; pediatrics; rare diseases

DOI: https://doi.org/10.1002/jgc4.1856

Glycobiology. 2024 Jan 15. pii: cwae004. [Epub ahead of print]

GNE deficiency impairs Myogenesis in C2C12 cells and cannot be rescued by ManNAc supplementation.

Carolin T Neu, Linus Weilepp, Kaya Bork, Astrid Gesper, Rüdiger Horstkorte.

GNE myopathy (GNEM) is a late-onset muscle atrophy, caused by mutations in the gene for the key enzyme of sialic acid biosynthesis, UDP-N-acetylglucosamine 2-epimerase/N-acetylmannosamine kinase (GNE). With an incidence of one to nine cases per million it is an ultra-rare, so far untreatable, autosomal recessive disease. Several attempts have been made to treat GNEM patients by oral supplementation with sialic acid precursors (e.g. N-acetylmannosamine, ManNAc) to restore sarcolemmal sialylation and muscle strength. In most studies, however, no significant improvement was observed. The lack of a suitable mouse model makes it difficult to understand the exact pathomechanism of GNEM and many years of research have failed to identify the role of GNE in skeletal muscle due to the lack of appropriate tools. We established a CRISPR/Cas9-mediated Gne-knockout cell line using murine C2C12 cells to gain insight into the actual role of the GNE enzyme and sialylation in a muscular context. The main aspect of this study was to evaluate the therapeutic potential of ManNAc and N-acetylneuraminic acid (Neu5Ac). Treatment of Gne-deficient C2C12 cells with Neu5Ac, but not with ManNAc, showed a restoration of the sialylation level back to wild type levels-albeit only with long-term treatment, which could explain the rather low therapeutic potential. We furthermore highlight the importance of sialic acids on myogenesis, for C2C12 Gne-knockout myoblasts lack the ability to differentiate into mature myotubes.

Keywords: GNE; GNE myopathy; Polysialylation; Posttranslational modification; Sialic acid biosynthesis

DOI: https://doi.org/10.1093/glycob/cwae004

J Health Monit. 2023 Dec;8(4): 7-16

Rare diseases in Germany - Developments in the status of medical care.

Miriam Schlangen, Katharina Heuing.

Background: Rare diseases are a heterogeneous group of complex clinical patterns, which more often than not run a chronic course. The fact that they are rare complicates the provision of medical care for the specific diseases.
Results: In the field of action titled 'Care, Centres, Networks' of its National Action Plan, the National Action League for People with Rare Diseases recommends the formation of a three-level, interconnected centre model. This form of care was investigated in two large research projects. It was shown that the time to diagnosis was markedly reduced. Commissioned by the Federal Ministry of Health, the expert report on the health status of people with rare diseases in Germany issued in 2023 concludes that the medical care provided to this group of people has improved markedly since the National Action Plan was introduced. The establishment of the Centres for Rare Diseases (ZSE, Zentren für Seltene Erkrankungen) is seen as the most important development. However, it is noted that there is still a lack of coordinated care provision pathways for referring patients to the appropriate facilities.
Conclusion: The provision of care to people with rare diseases has improved upon the implementation of the measures from the National Action Plan. In a next step, care provision pathways must be established across sector boundaries. Challenges remain in the area of psychosocial care and the long-term securing of funding for these structures.

Keywords: CENTRE MODEL; CRITICAL PATHWAYS PATIENT CARE; GERMANY; NAMSE; NATIONAL ACTION PLAN; PATIENT PATHWAYS; RARE DISEASES

DOI: https://doi.org/10.25646/11746

Nat Rev Genet. 2024 Jan 18.

The expanding diagnostic toolbox for rare genetic diseases.

Kristin D Kernohan, Kym M Boycott.

Genomic technologies, such as targeted, exome and short-read genome sequencing approaches, have revolutionized the care of patients with rare genetic diseases. However, more than half of patients remain without a diagnosis. Emerging approaches from research-based settings such as long-read genome sequencing and optical genome mapping hold promise for improving the identification of disease-causal genetic variants. In addition, new omic technologies that measure the transcriptome, epigenome, proteome or metabolome are showing great potential for variant interpretation. As genetic testing options rapidly expand, the clinical community needs to be mindful of their individual strengths and limitations, as well as remaining challenges, to select the appropriate diagnostic test, correctly interpret results and drive innovation to address insufficiencies. If used effectively - through truly integrative multi-omics approaches and data sharing - the resulting large quantities of data from these established and emerging technologies will greatly improve the interpretative power of genetic and genomic diagnostics for rare diseases.

DOI: https://doi.org/10.1038/s41576-023-00683-w

Blood Adv. 2024 Jan 18. pii: bloodadvances.2023011490. [Epub ahead of print]

Novel GNE missense variants impair de novo sialylation and cause defective angiogenesis in the developing brain in mice.

Lulu Huang, Yuji Kondo, Lijuan Cao, Jingjing Han, Tianyi Li, Bin Zuo, Fei Yang, Yun Li, Zhenni Ma, Xia Bai, Miao Jiang, Changgeng Ruan, Lijun Xia.

Glucosamine (UDP-N-acetyl)-2-epimerase and N-acetylmannosamine (ManNAc) kinase (GNE) is a cytosolic enzyme in de novo sialic acid biosynthesis. Congenital deficiency of GNE causes an autosomal recessive genetic disorder associated with hereditary inclusion body myopathy and macrothrombocytopenia. Here, we report a pediatric patient with severe macrothrombocytopenia carrying two novel GNE missense variants, c.1781G>A (p.Cys594Tyr, hereafter, C594Y) and c.2204C>G (p.Pro735Arg, hereafter, P735R). To investigate the biological significance of these variants in vivo, we generated a mouse model carrying the P735R mutation. Mice with homozygous P735R mutations exhibited cerebral hemorrhages as early as embryonic day 11 (E11), which subsequently progressed to large hemorrhages in the brain and spinal cord, and died between E11.5 and E12.5. Defective angiogenesis such as distended vascular sprouts were found in neural tissues and embryonic megakaryocytes were abnormally accumulated in the perineural vascular plexus in mutant mouse embryos. Furthermore, our in vitro experiments indicated that both C594Y and P735R are loss-of-function mutations with respect to de novo sialic acid biosynthesis. Overall, this study reveals a novel role for GNE-mediated de novo sialic acid biosynthesis in mouse embryonic angiogenesis.

DOI: https://doi.org/10.1182/bloodadvances.2023011490