Looking for the skeleton in the closet-rare genetic diagnoses in patients with diabetes and skeletal manifestations

Transforming growth factor, beta-2 gene mutation causes autosomal dominant Camurati-Engelmann disease, type 2 (OMIM % 606631)

Camurati-Engelmann disease, type 1 (CED1, OMIM # 131300) is the rare autosomal dominant skeletal dysplasia caused by select heterozygous loss-of-function defects within the gene TGFB1, which encodes transforming growth factor beta 1 (TGFB1). CED1 mutations are found in TGFB1 exons 1-4 that form the latency-associated peptide (LAP) of pro-TGFB1. Consequently, skeletal action of TGFB1 increases and thereby enhances bone formation manifest clinically as "progressive diaphyseal dysplasia". Beginning 24 years ago negative TGFB1 analysis suggested rare genetic heterogeneity for CED, and Online Mendelian Inheritance In Man designated, of unknown etiology, "CED2" (OMIM % 606631). In 2024, three sporadic occurrences considered CED2 were reported to harbor either of two mutations of TGFB2, which encodes the LAP of transforming growth factor beta 2 (TGFB2). Herein, three adults (father, son, daughter) having the CED2 phenotype in a Peruvian family revealed a novel missense variant (c.108G > T, p.R36S) within the TGFB2 LAP domain. Debilitating painful skeletal disease featuring hyperostosis of entire long bones, worse in the men, presented early in childhood. Aminobisphosphonate therapy seemed helpful. Their TGFB2 variant was within a highly conserved domain across species, absent in the gnomAD database, "possibly damaging" by Polyphen-2, not tolerated by SIFT, homologous with TGFB1 at the same amino acid position (R36) as one reported TGFB2 mutation, co-segregated as autosomal dominant, and "likely pathogenic" per ACMG guidelines.

Discovery of a TRMT10A mutation in a case of atypical diabetes: Case report

It is notable that monogenic forms of diabetes are exceedingly uncommon, with only 28 genes thus far identified. Such conditions frequently result in the dysfunction of pancreatic cells responsible for insulin production. Mutation in the TRMT10A gene leads to a rare genetic disease that is associated with endocrine and metabolic disorders, including diabetes and short stature. This article presents a review of the existing literature on the subject, describing the association between TRMT10A gene mutation and diabetes. It also presents the clinical case of a young girl with type 1 diabetes and facial dysmorphia. TRMT10A gene mutation has been linked to syndromic juvenile diabetes in a manner analogous to Wolfram's syndrome. This form of diabetes, which manifests in early childhood and is associated with microcephaly, epilepsy and intellectual disability, is caused by mutations in the gene for homolog A of tRNA methyltransferase 10 (TRMT10A). This emphasizes the importance of using a targeted panel to recognize previously unidentified monogenic diabetes among early-onset non-insulin-dependent diabetes in the absence of obesity and autoimmunity. In view of the aforementioned data, it is recommended that TRMT10A sequencing be considered in children or adults with early-onset diabetes and a history of intellectual disability, microcephaly and epilepsy.

Methylation modifications in tRNA and associated disorders: Current research and potential therapeutic targets

High-throughput sequencing has sparked increased research interest in RNA modifications, particularly tRNA methylation, and its connection to various diseases. However, the precise mechanisms underpinning the development of these diseases remain largely elusive. This review sheds light on the roles of several tRNA methylations (m1A, m3C, m5C, m1G, m2G, m7G, m5U, and Nm) in diverse biological functions, including metabolic processing, stability, protein interactions, and mitochondrial activities. It further outlines diseases linked to aberrant tRNA modifications, related enzymes, and potential underlying mechanisms. Moreover, disruptions in tRNA regulation and abnormalities in tRNA-derived small RNAs (tsRNAs) contribute to disease pathogenesis, highlighting their potential as biomarkers for disease diagnosis. The review also delves into the exploration of drugs development targeting tRNA methylation enzymes, emphasizing the therapeutic prospects of modulating these processes. Continued research is imperative for a comprehensive comprehension and integration of these molecular mechanisms in disease diagnosis and treatment.

TRMT10A dysfunction perturbs codon translation of initiator methionine and glutamine and impairs brain functions in mice

In higher eukaryotes, tRNA methyltransferase 10A (TRMT10A) is responsible for N1-methylguanosine modification at position nine of various cytoplasmic tRNAs. Pathogenic mutations in TRMT10A cause intellectual disability, microcephaly, diabetes, and short stature in humans, and generate cytotoxic tRNA fragments in cultured cells; however, it is not clear how TRMT10A supports codon translation or brain functions. Here, we generated Trmt10a null mice and showed that tRNAGln(CUG) and initiator methionine tRNA levels were universally decreased in various tissues; the same was true in a human cell line lacking TRMT10A. Ribosome profiling of mouse brain revealed that dysfunction of TRMT10A causes ribosome slowdown at the Gln(CAG) codon and increases translation of Atf4 due to higher frequency of leaky scanning of its upstream open reading frames. Broadly speaking, translation of a subset of mRNAs, especially those for neuronal structures, is perturbed in the mutant brain. Despite not showing discernable defects in the pancreas, liver, or kidney, Trmt10a null mice showed lower body weight and smaller hippocampal postsynaptic densities, which is associated with defective synaptic plasticity and memory. Taken together, our study provides mechanistic insight into the roles of TRMT10A in the brain, and exemplifies the importance of universal tRNA modification during translation of specific codons.

Monogenic diabetes clinic (MDC): 3-year experience

AIM

In the pediatric diabetes clinic, patients with type 1 diabetes mellitus (T1D) account for more than 90% of cases, while monogenic forms represent about 6%. Many monogenic diabetes subtypes may respond to therapies other than insulin and have chronic diabetes complication prognosis that is different from T1D. With the aim of providing a better diagnostic pipeline and a tailored care for patients with monogenic diabetes, we set up a monogenic diabetes clinic (MDC).

METHODS

In the first 3 years of activity 97 patients with non-autoimmune forms of hyperglycemia were referred to MDC. Genetic testing was requested for 80 patients and 68 genetic reports were available for review.

RESULTS

In 58 subjects hyperglycemia was discovered beyond 1 year of age (Group 1) and in 10 before 1 year of age (Group 2). Genetic variants considered causative of hyperglycemia were identified in 25 and 6 patients of Group 1 and 2, respectively, with a pick up rate of 43.1% (25/58) for Group 1 and 60% (6/10) for Group 2 (global pick-up rate: 45.5%; 31/68). When we considered probands of Group 1 with a parental history of hyperglycemia, 58.3% (21/36) had a positive genetic test for GCK or HNF1A genes, while pick-up rate was 18.1% (4/22) in patients with mute family history for diabetes. Specific treatments for each condition were administered in most cases.

CONCLUSION

We conclude that MDC may contribute to provide a better diabetes care in the pediatric setting.