Transient neonatal diabetes mellitus in a Turkish patient with three novel homozygous variants in the ZFP57 gene

Neonatal diabetes due to homozygous INS gene promoter mutations: Highly variable phenotype, remission and early relapse during the first 3 years of life

Neonatal diabetes mellitus (NDM) is a rare form of monogenic diabetes presenting within the first 6 months of life. INS gene promoter mutations have been shown to cause both remitting/relapsing and permanent NDM. We, herein, present three interesting patients with INS gene promoter mutations. Two cousins with an identical homozygous c.-331C > G mutation presented with NDM. The first cousin had nonremitting diabetes and still requires multidose insulin injections at the current age of 6.1 years. However, the other cousin's diabetes remitted at the age of 9 months, and she is still in remission at the age of 3 years with no medication or dietary intervention required (latest HbA1c was 4.9%). The third patient had NDM also due to a homozygous INS promoter c.-331C>A mutation. Her diabetes remitted at the age of 2 months and relapsed at the age of 2.6 years with severe diabetic ketoacidosis (DKA). Distinct clinical phenotype and relapse with severe DKA in one of the three cases suggest that INS promotor mutations can cause a heterogeneous phenotype and even cases exhibiting remission can relapse unpredictably. Therefore, as the age of relapse is unpredictable, close follow-up and family education on diabetes symptoms are essential for cases with remitting/relapsing diabetes due to INS gene mutations.

Transient neonatal diabetes mellitus and hypomethylation at additional imprinted loci: novel ZFP57 mutation and review on the literature

AIM

6q24-related transient neonatal diabetes mellitus (6q24-TNDM) is a rare imprinting disorder characterized by uncontrolled hyperglycemia during the first 6 months of life. The molecular etiology of 6q24-TNDM is attributable to overexpression of the paternally inherited PLAGL1 and HYMAI genes located on the 6q24 locus. One of these major defects is maternal loss of methylation (LOM) at 6q24. In addition, approximately 50% of TNDM patients that present LOM at 6q24 can also display hypomethylation at additional imprinted loci (multilocus imprinting disturbances, MLID). Interestingly, the majority of these patients carry mutations in the ZFP57 gene, a transcription factor required for the adequate maintenance of methylation during early embryonic development.

METHODS

Methylation analysis of 6q24 and additional imprinted loci was carried out by MS-MLPA in a Tunisian male patient with clinical diagnosis of TNMD. For the same patient, mutation analysis of the ZFP57 gene was conducted by direct Sanger sequencing.

RESULTS

We report a novel nonsense mutation (c.373C > T; p.R125*; ENST00000376883.1) at the ZFP57 gene causing TNDM-MLID and describe detailed phenotype/epigenotype analysis of TNMD patients carrying ZFP57 mutations.

CONCLUSION

We provide additional support to the role of ZFP57 as a genetic determinant cause of MLID in patients with TNMD.

A Newborn with Transient Diabetes Mellitus Accompanied by Ketoacidosis Attributable to a ZFP57 Mutation

Hyperglycemia commencing within the first 6 months of life requires exogenous insulin therapy and, if the condition persists for >2 weeks, is termed neonatal diabetes mellitus (NDM). This rare illness is of two types: transient and permanent NDM. Most cases come to medical attention because of nonspecific symptoms, including intrauterine growth retardation, dehydration, difficulties in feeding and inadequate weight gain. In the present article, we describe an infant who smelt of ketones during examination and who was diagnosed with transient NDM caused by a ZFP57 mutation, accompanied by ketoacidosis. This is the first report of such a condition.

Potential Roles of Intrinsic Disorder in Maternal-Effect Proteins Involved in the Maintenance of DNA Methylation

DNA methylation is an important epigenetic modification that needs to be carefully controlled as a prerequisite for normal early embryogenesis. Compelling evidence now suggests that four maternal-effect proteins, primordial germ cell 7 (PGC7), zinc finger protein 57 (ZFP57), tripartite motif-containing 28 (TRIM28) and DNA methyltransferase (cytosine-5) 1 (DNMT1) are involved in the maintenance of DNA methylation. However, it is still not fully understood how these maternal-effect proteins maintain the DNA methylation imprint. We noticed that a feature common to these proteins is the presence of significant levels of intrinsic disorder so in this study we started from an intrinsic disorder perspective to try to understand these maternal-effect proteins. To do this, we firstly analysed the intrinsic disorder predispositions of PGC7, ZFP57, TRIM28 and DNMT1 by using a set of currently available computational tools and secondly conducted an intensive literature search to collect information on their interacting partners and structural characterization. Finally, we discuss the potential effect of intrinsic disorder on the function of these proteins in maintaining DNA methylation.

Causes and Consequences of Multi-Locus Imprinting Disturbances in Humans

Eight syndromes are associated with the loss of methylation at specific imprinted loci. There has been increasing evidence that these methylation defects in patients are not isolated events occurring at a given disease-associated locus but that some of these patients may have multi-locus imprinting disturbances (MLID) affecting additional imprinted regions. With the recent advances in technology, methylation profiling has revealed that imprinted loci represent only a small fraction of the methylation differences observed between the gametes. To figure out how imprinting anomalies occur at multiple imprinted domains, we have to understand the interplay between DNA methylation and histone modifications in the process of selective imprint protection during pre-implantation reprogramming, which, if disrupted, leads to these complex imprinting disorders (IDs).