High carrier frequency of a nonsense p.Trp230* variant in HSD3B2 gene in Ossetians.

Background: Congenital adrenal hyperplasia (CAH) caused by 3ß-HSD deficiency is a rare form of congenital adrenal deficiency with an autosomal recessive type of inheritance. Previously we have demonstrated that a single nucleotide variant (SNV) p.Trp230* in the homozygous state is a frequent cause of CAH among the indigenous population of North Ossetia-Alania represented by Ossetians. Methods: Genotyping of the NM_000198.3:c.690G>A p.Trp230* variant was performed by Real-time PCR. 339 healthy individuals of Ossetian origin were included in the study. Allele frequencies, Fisher's confidence intervals (CI) were calculated using the WinPepi v. 11.65 software. Comparison of allele frequencies was performed with the z-score test for two proportions. Results: Eight heterozygous carriers of c.690G>A variant in HSD3B2 gene were detected in 339 samples investigated. The total allele frequency of p.Trp230* variant was 0.0118 (n=8/678, 95% CI=0.0051-0.0231). Accordingly, the heterozygous carrier rate was 0.0236 (n=8/339). The frequency of CAH caused by p.Trp230* variant in HSD3B2 in Ossetian population was 1:7183 or 13.9 per 100,000 (95% CI: 1:1874-1:38447 or 3-53 per 100,000). Conclusion: The results demonstrate high frequency of p.Trp230* variant in Ossetians, which is most likely attributed to a founder effect.

Insulinoma in childhood: a retrospective review of 22 patients from one referral centre.

Background: Insulinomas are very rare in childhood with sparse knowledge on the clinical aspects and the presence of Multiple Endocrine Neoplasia type 1 (MEN1). Methods: We conducted a retrospective review of patients diagnosed with insulinoma between 1995 and 2021, presenting to one referral centre in Russia. Clinical, biochemical, genetic, imaging and histological data were collected. In addition, follow-up and family data were obtained. Results: A total of twenty-two children aged 5 to 16 years were identified. The median (range) gap between the first hypoglycaemia symptoms and diagnosis was 10 (1-46) months. Twelve children (55%) were misdiagnosed to have epilepsy and were treated with anticonvulsants before hypoglycemia was revealed. Contrast enhanced MRI and/or CT were accurate to localize the lesion in 82% (n=18). Five patients (23%) had multiple pancreatic lesions. All children underwent surgical treatment. The median (range) diameter of removed tumors was 1.5 (0.3-6) cm. Histopathological studies confirmed the presence of insulinoma in all cases. Immunohistochemical studies revealed G2 differentiation grade in 10 out of 17 cases. Two patients were diagnosed with metastatic insulinoma. One of them had metastases at the time of insulinoma diagnosis, while the other was diagnosed with liver metastases eight years after the surgery. Eight children (36%) were found to carry MEN1 mutations, inherited n=5, de novo n=1, no data, n=2. Children with MEN1 had significantly higher number of pancreatic tumors compared to sporadic cases. All of them developed additional MEN1 symptoms during the following 2-13 years. In the five patients with inherited MEN1, seven family members had hitherto undiscovered MEN1 manifestations. Conclusions: In this large cohort of children with rare pediatric insulinomas, MEN1 syndrome and G2 tumors were frequent, as well as hitherto undiscovered MEN1 manifestations in family members. Our data emphasize the need of genetic testing in all children with insulinoma and their relatives, even in the absence of any other features, as well as the importance of a prolonged follow-up observation.

Spectrum of neuro-developmental disorders in children with congenital hyperinsulinism due to activating mutations in GLUD1.

Background: Hyperinsulinism/hyperammonemia (HI/HA) syndrome is the second most common type of congenital hyperinsulinism caused by an activating GLUD1 mutation. Objective: The aim of this study was to determine the clinical profile and long-term neurological outcomes in children with HI/HA syndrome. Method: This study is a retrospective review of patients with GLUD1 mutation, treated at two centers in the UK and Russia, over a 15-year period. Different risk factors for neuro-developmental disorders were analysed by Mann-Whitney U test and Fisher's exact P test. Results: We identified 25 cases with GLUD1 mutations (12 males). Median age of presentation was 7 months (12 h-18 months). Hypoglycaemic seizures were the presenting feature in 24 (96%) cases. Twenty four cases responded to diazoxide and protein restriction whilst one patient underwent partial pancreatectomy. In total, 13 cases (52%) developed neurodevelopmental manifestations. Epilepsy (n = 9/25, 36%), learning difficulties (n = 8/25, 32%) and speech delay (n = 8/25, 32%) were the most common neurological manifestation. Median age of presentation for epilepsy was 12 months with generalised tonic-clonic seizures being the most common (n = 4/9, 44.4%) followed by absence seizures (n = 3/9, 33.3%). Early age of presentation (P = 0.02), diazoxide dose (P = 0.04) and a mutation in exon 11 or 12 (P = 0.01) were associated with neurological disorder. Conclusion: HI/HA syndrome is associated with wide spectrum of neurological disorders. These neurological manifestations were more frequent in cases with mutations affecting the GTP-binding site of GLUD1 in our cohort.

Assessment of efficacy and safety of volanesorsen for treatment of metabolic complications in patients with familial partial lipodystrophy: Results of the BROADEN study: Volanesorsen in FPLD; The BROADEN Study.

BACKGROUND: Volanesorsen, an antisense oligonucleotide, is designed to inhibit hepatic apolipoprotein C-III synthesis and reduce plasma apolipoprotein C-III and triglyceride concentrations. OBJECTIVE: The present study assessed efficacy and safety of volanesorsen in patients with familial partial lipodystrophy (FPLD) and concomitant hypertriglyceridemia and diabetes. METHODS: BROADEN was a randomized, placebo-controlled, phase 2/3, 52-week study with open-label extension and post-treatment follow-up periods. Patients received weekly subcutaneous volanesorsen 300 mg or placebo. The primary endpoint was percent change from baseline in fasting triglycerides at 3 months. Secondary endpoints included relative percent change in hepatic fat fraction (HFF), visceral adiposity, and glycated hemoglobin levels. RESULTS: Forty patients (11 men, 29 women) were enrolled, majority of whom were aged <65 years (mean, 47 years) and White. Least squares mean (LSM) percent change in triglycerides from baseline to 3 months was -88% (95% CI, -134 to -43) in the volanesorsen group versus -22% (95% CI, -61 to 18) in the placebo group, with a difference in LSM of -67% (95% CI, -104 to -30; P=0.0009). Volanesorsen induced a significant LSM relative reduction in HFF of 53% at month 12 versus placebo (observed mean [SD]: 9.7 [7.65] vs. 18.0 [8.89]; P=0.0039). No statistically significant changes were noted in body volume measurements (fat, liver, spleen, visceral/subcutaneous adipose tissue) or glycated hemoglobin. Serious adverse events in patients assigned to volanesorsen included 1 case each of sarcoidosis, anaphylactic reaction, and systemic inflammatory response syndrome. CONCLUSION: In BROADEN, volanesorsen significantly reduced serum triglyceride levels and hepatic steatosis in patients with FPLD.

Aberrant Splicing of INS Impairs Beta-Cell Differentiation and Proliferation by ER Stress in the Isogenic iPSC Model of Neonatal Diabetes.

One of the causes of diabetes in infants is the defect of the insulin gene (INS). Gene mutations can lead to proinsulin misfolding, an increased endoplasmic reticulum (ER) stress and possible beta-cell apoptosis. In humans, the mechanisms underlying beta-cell failure remain unclear. We generated induced pluripotent stem cells (iPSCs) from a patient diagnosed with neonatal diabetes mellitus carrying the INS mutation in the 2nd intron (c.188-31G>A) and engineered isogenic CRISPR/Cas9 mutation-corrected cell lines. Differentiation into beta-like cells demonstrated that mutation led to the emergence of an ectopic splice site within the INS and appearance of the abnormal RNA transcript. Isogenic iPSC lines differentiated into beta-like cells showed a clear difference in formation of organoids at pancreatic progenitor stage of differentiation. Moreover, MIN6 insulinoma cell line expressing mutated cDNA demonstrated significant decrease in proliferation capacity and activation of ER stress and unfolded protein response (UPR)-associated genes. These findings shed light on the mechanism underlying the pathogenesis of monogenic diabetes.

A Founder Mutation in the POMC 5'-UTR Causes Proopiomelanocortin Deficiency Through Splicing-Mediated Decrease of mRNA.

CONTEXT: The syndrome of adrenal insufficiency, obesity, and red hair is a rare autosomal recessive disorder. The majority of disease-causing variants associated with the syndrome are located in the coding region of the POMC gene. OBJECTIVE: This work describes 7 unrelated patients who shared a novel homozygous mutation in the 5'-untranslated region (UTR) of the POMC gene and functionally characterize this novel variant. METHODS: Whole-exome sequencing (WES) with autozygosity mapping, Sanger sequencing, model expression system studies, and RNA sequencing were used for identification of the disease-causing variant and its subsequent functional characterization. Seven unrelated patients of the Perm Tatar ethnic group presented with hypoglycemia and excessive weight gain, low plasma adrenocorticotropin, and cortisol. Five of 7 children had red hair; 6 of 7 patients also showed signs of bronchial obstruction. RESULTS: WES showed shared autozygosity regions overlapping the POMC gene. Sanger sequencing of the POMC 5'-UTR detected a homozygous variant chr2:25391366C > T (hg19) at the splice donor site of intron 1. As demonstrated by the model expression system, the variant led to a significant decrease in the POMC messenger RNA level. Analyses of the patients' haplotypes were suggestive of the founder effect. We estimate that the mutation must have occurred at least 4.27 generations ago (95% CI, 0.86-7.67). CONCLUSION: This report presents a new molecular mechanism of POMC deficiency and contributes to the information on phenotypic variability in patients with this disorder.

The coincidence of two rare diseases with opposite metabolic phenotype: a child with congenital hyperinsulinism and Bloom syndrome.

OBJECTIVES: Congenital hyperinsulinism (CHI) is a group of rare genetic disorders characterized by insulin overproduction. CHI causes life-threatening hypoglycemia in neonates and infants. Bloom syndrome is a rare autosomal recessive disorder caused by mutations in the BLM gene resulting in genetic instability and an elevated rate of spontaneous sister chromatid exchanges. It leads to insulin resistance, early-onset diabetes, dyslipidemia, growth delay, immune deficiency and cancer predisposition. Recent studies demonstrate that the BLM gene is highly expressed in pancreatic islet cells and its mutations can alter the expression of other genes which are associated with apoptosis control and cell proliferation. CASE PRESENTATION: A 5-month-old female patient from consanguineous parents presented with drug-resistant CHI and dysmorphic features. Genetic testing revealed a homozygous mutation in the KCNJ11 gene and an additional homozygous mutation in the BLM gene. While 18F-DOPA PET scan images were consistent with a focal CHI form and intraoperative frozen-section histopathology was consistent with diffuse CHI form, postoperative histopathological examination revealed features of an atypical form. CONCLUSIONS: In our case, the patient carries two distinct diseases with opposite metabolic phenotypes.

Serum circulating miRNA-342-3p as a potential diagnostic biomarker in parathyroid carcinomas: A pilot study.

OBJECTIVE: To compare the serum miRNA expression profiles between patients with benign and malignant parathyroid tumours. BACKGROUND: Despite recent advances in molecular biology, a histological tissue biopsy is still the method of choice used to diagnose most cancers. The preoperative cytology is not an applicable method for diagnosis of parathyroid cancer (PC); therefore, huge interest exists in terms of finding alternative methodologies to seek specific cancer biomarkers. DESIGN: A retrospective cross-sectional study. PATIENTS AND METHODS: Serum samples of patients with PC (n = 13) and parathyroid adenoma (PA) (n = 11), age (p = .999) and sex (p = .999) were matched and examined via the simultaneous comparative expression analysis of 754 microRNAs (miRNAs). The «TaqMan OpenArray Human MicroRNA Panel¼ (Applied Biosystems) was used to conduct real-time PCRs using the «QuantStudio 12К Flex¼ station (Life Technologies). RESULTS: According to the results of a pilot study, significant changes in expression levels between the PC group and the PA group (control) (p < .05) were observed for 17 miRNAs. Among them, the downregulation of miRNA-342-3p met the Benjamini-Hochberg adjustment criteria for multiple comparisons (p = .02). CONCLUSIONS: Serum miRNA-342-3p could be a promising biomarker for PC to improve diagnosis and prognosis.

Generation of an induced pluripotent stem cell line HPCASRi002-A from a patient with neonatal severe primary hyperparathyroidism caused by a compound heterozygous mutation in the CASR gene.

Neonatal severe primary hyperparathyroidism (NSHPT) is a rare autosomal recessive disorder of calcium homeostasis that manifests shortly after birth with hypercalcemia and bone disease. NSHPT, in most cases, is attributed to mutations in the calcium-sensing receptor (CASR) gene. We reprogrammed dermal fibroblasts derived from a patient with NSHPT carrying a compound heterozygous mutation in the CASR gene into induced pluripotent stem cells (iPSCs). The established iPSCs expressed pluripotency markers, maintained normal karyotype and differentiated into all three germ layers. This line is a valuable resource for modeling of hyperparathyroidism related to CASR mutations.

Familial Acromegaly and Bilateral Asynchronous Pheochromocytomas in a Female Patient With a MAX Mutation: A Case Report.

Background: There are very few cases of co-occurring pituitary adenoma (PA) and pheochromocytomas (PCC)/paragangliomas caused by MAX mutations. No cases of familial PA in patients with MAX mutations have been described to date. Case Presentation: We describe a 38-year-old female patient, presenting with clinical and biochemical features of acromegaly and PCC of the left adrenal gland. Whole-exome sequencing was performed [NextSeq550 (Illumina, San Diego, CA, USA)] identifying a nonsense mutation in the MAX gene (NM_002382) [c.223C>T (p.R75X)]. The patient had a medical history of PCC of the right adrenal gland diagnosed aged 21 years and prolactinoma diagnosed aged 25 years. Cabergoline treatment was effective in achieving remission of prolactinoma at age 33 years. The patient's father who died at age 56 years of a heart attack had a medical history of PA and prominent acromegalic features, which supports the familial presentation of the disease. Conclusion: This clinical case gives an insight into the clinical presentation of familial PA and PCC probably associated with a MAX mutation.

Atypical progeroid syndrome (p.E262K LMNA mutation): a rare cause of short stature and osteoporosis.

SUMMARY: Lamin A/C (LMNA) gene mutations cause a heterogeneous group of progeroid disorders, including Hutchinson-Gilford progeria syndrome, mandibuloacral dysplasia, atypical progeroid syndrome (APS) and generalized lipodystrophy-associated progeroid syndrome (GLPS). All of those syndromes are associated with some progeroid features, lipodystrophy and metabolic complications but vary differently depending on a particular mutation and even patients carrying the same gene variant are known to have clinical heterogeneity. We report a new 30-year-old female patient from Russia with an APS and generalized lipodystrophy (GL) due to the heterozygous de novo LMNA p.E262K mutation and compare her clinical and metabolic features to those of other described patients with APS. Despite many health issues, short stature, skeletal problems, GL and late diagnosis of APS, our patient seems to be relatively metabolically healthy for her age when compared to previously described patients with APS. LEARNING POINTS: Atypical progeroid syndromes (APS) are rare and heterogenic with different age of onset and degree of metabolic disorders, which makes this diagnosis very challenging for clinicians and may be missed until the adulthood. The clinical picture of the APS depends on a particular mutation in the LMNA gene, but may vary even between the patients with the same mutation. The APS due to a heterozygous LMNA p.E262K mutation, which we report in this patient, seems to have association with the generalized lipodystrophy, short stature and osteoporosis, but otherwise, it seems to cause relatively mild metabolic complications by the age of 30. The patients with APS and lipodystrophy syndromes require a personalized and multidisciplinary approach, and so they should be referred to highly specialized reference-centres for diagnostics and treatment as early as possible. Because of the high heterogeneity of such a rare disease as APS, every patient's description is noteworthy for a better understanding of this challenging syndrome, including the analysis of genotype-phenotype correlations.

Clinical Outcomes and Complications of Pituitary Blastoma.

CONTEXT: Pituitary blastoma is a rare, dysontogenetic hypophyseal tumor of infancy first described in 2008, strongly suggestive of DICER1 syndrome. OBJECTIVE: This work aims to describe genetic alterations, clinical courses, outcomes, and complications in all known pituitary blastoma cases. DESIGN AND SETTING: A multi-institutional case series is presented from tertiary pediatric oncology centers. PATIENTS: Patients included children with pituitary blastoma. INTERVENTIONS: Genetic testing, surgery, oncologic therapy, endocrine support are reported. OUTCOME MEASURES: Outcome measures included survival, long-term morbidities, and germline and tumor DICER1 genotypes. RESULTS: Seventeen pituitary blastoma cases were studied (10 girls and 7 boys); median age at diagnosis was 11 months (range, 2-24 months). Cushing syndrome was the most frequent presentation (n = 10). Cushingoid stigmata were absent in 7 children (2 with increased adrenocorticotropin [ACTH]; 5 with normal/unmeasured ACTH). Ophthalmoplegia and increased intracranial pressure were also observed. Surgical procedures included gross/near-total resection (n = 7), subtotal resection (n = 9), and biopsy (n = 1). Six children received adjuvant therapy. At a median follow-up of 6.7 years, 9 patients were alive; 8 patients died of the following causes: early medical/surgical complications (n = 3), sepsis (n = 1), catheter-related complication (n = 1), aneurysmal bleeding (n = 1), second brain tumor (n = 1), and progression (n = 1). Surgery was the only intervention for 5 of 9 survivors. Extent of resection, but neither Ki67 labeling index nor adjuvant therapy, was significantly associated with survival. Chronic complications included neuroendocrine (n = 8), visual (n = 4), and neurodevelopmental (n = 3) deficits. Sixteen pituitary blastomas were attributed to DICER1 abnormalities. CONCLUSIONS: Pituitary blastoma is a locally destructive tumor associated with high mortality. Surgical resection alone provides long-term disease control for some patients. Quality survival is possible with long-term neuroendocrine management.

[Clinical and molecular characteristics of patients with 46,XY DSD due to NR5A1 gene mutations].

Steroidogenic factor 1 (SF1, NR5A1) is a nuclear receptor that regulates multiple genes involved in adrenal and gonadal development, steroidogenesis, and the reproductive axis. Human mutations in SF1 were initially found in patients with severe gonadal dysgenesis and primary adrenal failure. However, more recent case reports have suggested that heterozygous mutations in SF1 may also be found in patients with 46,XY partial gonadal dysgenesis and underandrogenization but normal adrenal function. We have analyzed the gene encoding SF1 (NR5A1) in a cohort of 310 Russian patients with 46,XY disorders of sex development (DSD). Heterozygous SF1 variants were found in 36 out of 310 (11.6%) of cases, among them 15 were not previously described. We have not found any phenotype-genotype correlations and any clinical and laboratory markers that would allow to suspect this type of before conducting molecular genetic analysis.

[Dizygotic pregnancy as a possible mechanism of fetal gestation with a biallel mutation in the CYP11A1 gene: clinical case description].

One of the variants of congenital dysfunction of the adrenal cortex is a deficiency of the enzyme P450scc, which catalyzes the first stage of steroidogenesis. This is a rare autosomal recessive disease, the classic manifestation of which is primary adrenal insufficiency with a deficiency of gluco-and mineralocorticoids and a violation of the synthesis of sex steroids, which usually leads to a complete lack of masculinization in patients with karyotype 46, XY and hypergonadotropic hypogonadism in both sexes. Previously, it was suggested That p450scc deficiency is incompatible with the normal course of pregnancy, since the enzyme is expressed in the placenta, where it is necessary for the synthesis of progesterone, the main pregnancy hormone, and, consequently, the birth of a child with A p450scc deficiency is impossible. However, the literature describes clinical cases of p450scc deficiency with partially preserved enzyme function, which explains the normal course of pregnancy. Whereas cases of confirmed p450scc deficiency with zero enzyme activity are unique, not being explained until now. We present a description of severe p450scc deficiency in a child born from a dizygotic twin pregnancy in which the second Sib was healthy. It is possible that the preserved hormonal function of the second placenta and (or) treatment with progesterone analogs during gestation contributed to gestation in this rare form of steroidogenesis disorder.

Successful Use of Denosumab for Life-Threatening Hypercalcemia in a Pediatric Patient with Primary Hyperparathyroidism.

INTRODUCTION: Primary hyperparathyroidism (PHPT) is rare and usually symptomatic in children. There is no approved medication to lower serum calcium levels in this patient group. Denosumab is used in adult patients with osteoporosis and hyperparathyroidism. To our knowledge, only 1 case of denosumab treatment in a child with severe PHPT has been reported to date. CASE PRESENTATION: A 16-year-old female was referred to our clinic with symptoms including pathologic fractures, nausea, emesis, and progressive weight loss. At admission, her serum total calcium was 4.17 mmol/L (reference range 2.15-2.55), parathyroid hormone 2,151 pg/mL (15-65), and phosphate 1.07 mmol/L (1.45-1.78). Due to potentially life-threatening hypercalcemia, denosumab 60 mg subcutaneously was administered after obtaining informed consent. Serum calcium levels were reduced within 12 h of injection and the patient's condition rapidly improved, which allowed genetic testing to be done prior to surgery. A heterozygous mutation in the CDC73 gene was revealed, and a parathyroidectomy was performed on day 22 after denosumab administration. Morphological examination revealed solitary parathyroid adenoma. After surgery, hypocalcemia developed requiring high doses of alfacalcidol and calcium supplements. CONCLUSION: Our case supports the previous observations in adults that denosumab can be safely and effectively used as a preoperative treatment in patients with PHPT and severe hypercalcemia and shows that it may be used in pediatric patients.

Generation of an induced pluripotent stem cell line MNDINSi001-A from a patient with neonatal diabetes caused by a heterozygous INS mutation.

Insulin gene (INS) mutations prove to be the second most common cause of permanent neonatal diabetes. Here, we report the generation of iPSC line from a patient, heterozygous for the intronic INS mutation that presumably leads to aberrant splicing. Dermal fibroblasts were reprogrammed using non-integrating RNA-based vector. Derivation and expansion of iPSCs were performed under feeder-free culture conditions. The iPSC line expressed pluripotency markers, had normal karyotype, could differentiate into three germ layers in vitro and retained the disease mutation. This line can be a powerful tool for modeling of diabetes and cell replacement therapy as well.

Unusual clinical features associated with congenital generalized lipodystrophy type 4 in a patient with a novel E211X CAVIN1 gene variant.

BACKGROUND: Congenital generalized lipodystrophy (CGL) is a rare disorder characterized by the lack of adipose tissue and metabolic complications with predominantly autosomal recessive inheritance. There are 6 different genes known to cause CGL with 4 main types recognized to date, which differ by the degree of fat loss, association with mental retardation and metabolic disorders, with CGL type 1 and 2 being the most common. Twenty seven cases of СGL type 4 from Japan, Oman, UK, Turkey, Mexico, Saudi Arabia, USA were reported previously. This report details our clinical experience with the first patient from Russia with CGL type 4. CASE PRESENTATION: A 36-year-old patient, who has been suffering from generalized lipoatrophy since the first months of life and myopathy and gastrointestinal dysmotility since early childhood, developed dysmenorrhea and diabetes mellitus at the age of 19, bilateral cataracts when she was only 22 y.o., osteoporosis with vitamin D deficiency and hypocalcemia at the age of 28, diabetic foot syndrome and hyperuricemia when she was 35 y.o. Sequencing of lipodystrophy candidate genes detected a novel pathogenic homozygous variant p.631G < T: p.E211X in the CAVIN1 gene, confirming the diagnosis of CGL type 4. CONCLUSIONS: In comparison with previously reported patients with CGL type 4, our patient has diabetes mellitus, vitamin D deficiency, hypocalcemia, bilateral cataracts and hyperuricemia. All these manifestations are known to be associated with other lipodystrophy syndromes, but to our knowledge it is the first time they have been reported to be associated with CGL type 4.

Minigene splicing assessment of 20 novel synonymous and intronic glucokinase gene variants identified in patients with maturity-onset diabetes of the young.

The next-generation sequencing (NGS) has become a routine method for diagnostics of inherited disorders. However, assessment of the discovered variants may be challenging, especially when they are not predicted to change the protein sequence. Here we performed a functional analysis of 20 novel or rare intronic and synonymous glucokinase (GCK) gene variants identified by targeted NGS in 1,130 patients with maturity-onset diabetes of the young. Human Splicing Finder, ver 3.1 and a precomputed index of splicing variants (SPIDEX) were used for in silico prediction. In vitro effects of GCK gene variants on splicing were tested using a minigene expression approach. In vitro effect on splicing was shown for 9 of 20 variants, including two synonymous substitutions. In silico and in vitro results matched in about 50% of cases. The results demonstrate that novel or rare apparently benign GCK gene variants should be regarded as potential splicing mutations.