Summary

Maturity-onset diabetes of the young (MODY) is a group of monogenic forms of diabetes mellitus characterized by early-onset diabetes with dominant inheritance of beta-cell dysfunction. There are few reports of the coinheritance of glucokinase (GCK) and hepatocyte nuclear factor 1 alpha gene (HNF1A) variants underlying MODY in patients. Herein, we describe a case involving combinations of monoallelic GCK and HNF1A variants associated with MODY. A 10-year-old Japanese girl with a three-generation family history of diabetes without obesity showed high levels of urinary glucose during a school screening test. Her glucose metabolism profile revealed 124 mg/dL of fasting glucose, 6.9% glycated hemoglobin (HbA1c), and 2.78 ng/mL of C-peptide immunoreactivity levels. In a 75-g oral glucose tolerance test, her base glucose, peak glucose, insulin resistance, and homeostasis model assessment of beta cell function levels were 124 mg/dL, 210 mg/dL (120 min), 1.71, and 33%, respectively. Based on the clinical phenotype of GCK-MODY, alimentary and exercise therapy without oral hypoglycemic agents were used to maintain her fasting glucose and HbA1c levels. We explored the coinheritance of MODY with GCK and HNF1A variants in this and past cases and found that careful clinical follow-up is required to firmly establish phenotypic features. Moreover, the accumulation of data on genetically confirmed MODY associated with the coinheritance of GCK and HNF1A variants will be useful for understanding genotype–phenotype correlations.

Learning points

• MODY is a group of monogenic forms of diabetes mellitus characterized by early-onset diabetes with the dominant inheritance of beta-cell dysfunction.

• MODY2 and MODY3 caused by heterozygous loss-of-function variants in the glucokinase (GCK) and hepatocyte nuclear factor 1 alpha (HNF1A) genes, respectively, are the most common forms of the disease.

• Few cases of MODY have previously been reported as being associated with the coinheritance of GCK and HNF1A variants.

• Careful clinical follow-up is required to firmly establish phenotypic features in the coinheritance of MODY with GCK and HNF1A variants.

• The accumulation of data on genetically confirmed MODY associated with the coinheritance of GCK and HNF1A variants will be useful for understanding genotype–phenotype correlations.

Summary

Congenital adrenal hyperplasia (CAH) is one of the most common inherited rare endocrine disorders. This case report presents two female siblings with delayed diagnosis of non-classical CAH 3β-hydroxysteroid dehydrogenase type 2 (3βHSD2D/HSD3B2) despite early hospital admission and apparent CAH manifestations such as infections, hirsutism, menstrual disturbances, and PCOS phenotype. Initially, sister 1 was misdiagnosed with PCOS and then 11-hydroxylase deficiency (CYP11B1), based on ultrasound, biochemical findings, and negative genetic testing for 21-hydroxylase deficiency (CYP21A2). Additional diagnostic workup was performed when sister 2also presented with symptoms of androgen excess. Genetic testing for CAH/steroid disorders finally revealed that both siblings were compound heterozygous for two variants in the HSD3B2 gene: a frameshift variant, c.558dup, p.(Thr187Hisfs*17) and a novel missense variant, c.65T>C, p.(Leu22Ser). A Synacthen test showed an insufficient cortisol increase. In vitro studies of the variants in a cell model revealed loss of function for the p.(Thr187Hisfs*17) and partial activity for p.(Leu22Ser) confirming non-classic CAH. Overlapping symptomatology and lack of specialized knowledge on steroid biosynthesis and associated rarest forms of CAH may explain the delayed diagnosis. However, with newer diagnostic methods comprising a less biased approach, very rare forms of non-classical CAH may no longer be overlooked in the future.

Learning points

• Non-classic 3βHSD2 is likely underdiagnosed.

• Late diagnosis of mild non-classic 3βHSD2 does occur and one should be aware of this diagnosis.

• Early diagnosis of NCCAH may prevent many consequences such as severe hirsutism, prolonged menstrual irregularities, infertility, or even adrenal crisis with severe infections.

• Comprehensive steroid profiling and genetic testing should be used earlier, especially when in doubt about a diagnosis.

Summary

Multiple endocrine neoplasia type 2 (MEN2) is a hereditary cancer syndrome caused by germline-activating pathogenic variants in the RET proto-oncogene. MEN2A is the most common subtype, with a risk for medullary thyroid cancer (MTC), pheochromocytoma (PHEO), and primary hyperparathyroidism (PHPT), whereas MEN2B is less common and associated with MTC and PHEO along with mucosal neuromas. Little is known about the specific RET germline heterozygous variant K666N. This variant has been described in very few families, and in most cases, patients were diagnosed with a very indolent MTC as the only feature. There is one case of MTC and bilateral PHEO. The RET K666N variant is not stratified yet by the American Thyroid Association, and data are limited on pathogenicity; therefore, appropriate screening and treatment of asymptomatic RET K666N carriers are unclear. Here, we report a family with a heterozygous germline RET K666N variant. The proband was identified when she experienced cardiogenic shock and multi-organ failure after an elective hysterectomy and subsequently was found to have PHEO, with genetic testing revealing the RET K666N germline variant. Patient consent was obtained through IRB protocol COMIRB #15-0516.

Learning Points

• The specific RET germline heterozygous variant K666N is rare and described in very few families, and in most cases, patients were diagnosed with a very indolent MTC as the only feature. Our proband is much younger and has PHEO, MTC, and PHPT.

• The RET K666N germline variant appears to be a low penetrance variant for MEN2.

Summary

Familial renal glucosuria (FRG) is a rare renal tubular disorder characterized by increased urinary glucose excretion despite normoglycemia. It is most commonly caused by pathogenic variants in the solute carrier family V member 2 (SLC5A2) gene. This gene encodes the sodium–glucose cotransporter 2, crucial for glucose reabsorption. We report the case of a 44-year-old male referred to the endocrinology outpatient clinic for unexplained glucosuria despite well-controlled diabetes mellitus with metformin and gliclazide therapy. His main complaints were nocturia and an unintentional 5 kg weight loss in 1 year. A 24-h urinary collection revealed overt glucosuria (23.3 g/1.73 m²/24 h), generalized aminoaciduria, and increased uric acid excretion (fractional excretion: 6.4%). Whole-exome sequencing revealed a novel heterozygous c.469-1G>A likely pathogenic variant in the SLC5A2 gene. Specific analysis of the maturity-onset diabetes of the young type (MODY) gene panel showed no pathogenic variants in the hepatocyte nuclear factor-1A (HNF-1A; MODY3) nor in other MODY-associated genes. We assume that the association of glucosuria, aminoaciduria, and increased uric acid excretion can be explained by the combination of diabetes and the likely pathogenic SLC5A2 variant in this patient. In conclusion, we describe a well-controlled diabetic patient with FRG, associated with a novel heterozygous c.469-1G>A likely pathogenic variant in the SLC5A2 gene.

Learning points

• The diagnosis of a renal tubular disorder should be considered in patients with unexplained glucosuria and diabetes mellitus, especially if the latter is well controlled.

• FRG usually presents with glucosuria but may be associated with generalized aminoaciduria and hyperuricosuria.

• Genetic analysis should be considered in patients with young-onset diabetes and glucosuria, particularly with a positive family history.

Summary

Pregnancy in the setting of metastatic paraganglioma is challenging, particularly in the context of tyrosine kinase use. We describe a 26-year-old female with a background of metastatic paraganglioma harboring a pathogenic SDHB variant, requiring sunitinib, which was withheld to facilitate the safe conception and delivery of a healthy baby. She required no alpha- or beta-blockade during her pregnancy and exhibited no signs of tumor progression or symptoms throughout this period. Historically, higher rates of fetal and maternal morbidity and mortality have been experienced in the setting of pregnancy. Although limited data exist on the management of metastatic paraganglioma in pregnant patients, this case suggests that careful treatment modifications, such as temporary tyrosine kinase therapy cessation and vigilant monitoring, can result in successful pregnancies without compromising maternal or fetal well-being.

Learning points

• Paraganglioma in pregnancy has been associated with poor fetal and maternal morbidity and mortality.

• Many of the treatment modalities for metastatic paraganglioma, including tyrosine kinase inhibitors, can affect fertility or cannot be utilized in pregnancy, necessitating the temporary suspension of these treatments.

• This case exemplifies that careful clinical and biochemical monitoring during pregnancy is required to avoid maternal and fetal harm while balancing the risk of disease progression off treatment.

Summary

RET mutations are implicated in 60% of medullary thyroid cancer (MTC) cases. The RET-selective tyrosine kinase inhibitor selpercatinib is associated with unprecedented efficacy compared to previous multi-kinase treatments. Langerhans cell histiocytosis (LCH) is a clonal histiocytic neoplasm usually driven by somatic BRAF mutations, resulting in dysregulated MAPK signalling. We describe a 22-year-old woman with metastatic MTC to regional lymph nodes, lung and liver. Tumour tissue harboured a somatic pathogenic RET variant p.(M918T) and selpercatinib was commenced. She experienced sustained clinical, biochemical and radiological responses. Two years later, she developed rapidly progressive apical lung nodules, prompting biopsy. Histopathology demonstrated LCH with a rare BRAF variant p.(V600_K601>D). The lung nodules improved with inhaled corticosteroids. We hypothesize that selective pressure from RET blockade may have activated a downstream somatic BRAF mutation, resulting in pulmonary LCH. We recommend continued vigilance for neoplasms driven by dysregulated downstream MAPK signalling in patients undergoing selective RET inhibition.

Learning points

• Patients with RET-altered MTC can experience rapid disease improvement and sustained disease stability with selective RET blockade (selpercatinib).

• LCH is a clonal neoplasm driven by MAPK activation, for which the most common mechanism is BRAF mutation.

• Both MTC and pulmonary LCH are driven by dysregulated MAPK signalling pathway activation.

• We hypothesise that the RET-specific inhibitor selpercatinib may have caused the activation of dormant LCH secondary to selective pressure and clonal proliferation.

Summary

Thyroid cancer is one of the most common manifestations of Cowden syndrome, yet the syndrome is rare. The incidence of Cowden syndrome is 1 in 200,000. The diagnosis can be made clinically when patients present with a combination of symptoms such as mucocutaneous lesions with a strong personal or family history of thyroid, breast, endometrial, and colorectal cancer. A high index of suspicion is required to provide a clinical diagnosis utilizing major and minor criteria. Once a clinical diagnosis is made, genetic testing for a PTEN mutation, a tumor suppressor gene, is recommended. Cancer surveillance should be performed for those with positive genetic testing as well as those with negative genetic testing who still meet clinical diagnostic criteria. We present two cases of Cowden syndrome: one case involving an increasing number of thyroid nodules in a patient with known Cowden syndrome and another patient with a strong family history of cancer, personal history of follicular thyroid cancer, and numerous colonic polyps on screening colonoscopy. These cases demonstrate how early diagnosis of Cowden syndrome can help detect early cancer in both the patient and affected relatives.

Learning points

• Diagnosing Cowden syndrome helps pre-risk stratification for early cancer screening.

• The diagnosis of Cowden syndrome can be made with a combination of major and minor criteria: any two major criteria with or without a minor criterion; one major and one minor criterion; or three minor criteria.

• Patients who meet the diagnostic criteria for Cowden syndrome should undergo genetic screening.

Summary

Kabuki syndrome is a genetic disorder characterised by distinctive facial features, developmental delays, and multisystem congenital anomalies. Endocrine complications such as premature thelarche and short stature are common, whereas disorders of glycaemic control are less frequent. We describe a 23-year-old white female referred to the diabetes clinic for hyperglycaemia during haemodialysis. She was subsequently diagnosed with Kabuki syndrome based on characteristic clinical features, confirmed by detecting a heterozygous pathogenic variant in KMT2D. She was known to have had multiple congenital anomalies at birth, including complex congenital heart disease and a single dysplastic ectopic kidney, and received a cadaveric transplanted kidney at the age of 13. She had hyperglycaemia consistent with post-transplant diabetes mellitus (DM) and was started on insulin. Examination at the time revealed truncal obesity. She developed acute graft rejection and graft failure 14 months post-transplant and she was started on haemodialysis. Her blood glucose levels normalised post-graft explant, but she was hyperglycaemic again during haemodialysis at the age of 23. Given her clinical phenotype, negative diabetes antibodies and normal pancreas on ultrasound, she was assumed to have type 2 DM and achieved good glycaemic control with gliclazide.

Learning points

• Involve clinical genetics early in the investigative pathway of sick neonates born with multiple congenital anomalies to establish a diagnosis to direct medical care.

• Consider the possibility of Kabuki syndrome (KS) in the differential diagnoses in any neonate with normal karyotyping or microarray analysis and with multiple congenital anomalies (especially cardiac, renal, or skeletal), dysmorphic facial features, transient neonatal hypoglycaemia and failure to thrive.

• Consider the possibility of diabetes as an endocrine complication in KS patients who are obese or who have autoimmune disorders.

Summary

Barakat syndrome, also called HDR syndrome, is a rare genetic disorder encompassing hypoparathyroidism (H), sensorineural deafness (D) and renal disease (R). A 64-year-old woman was referred to our endocrinology clinic for a switch in treatment (from dihydrotachysterol to calcitriol). She had progressive sensorineural deafness since the age of 18 and idiopathic hypoparathyroidism diagnosed at age of 36. Her medical history included osteoporosis with hip/spine fractures, nephrolithiasis and a family history of hearing loss, osteoporosis and kidney disease. The patient’s clinical presentation indicated Barakat syndrome. Genetic analysis found a GATA3:c.916C>T nonsense variant. Further tests such as audiometry, labs and renal imaging supported the diagnosis. Due to rarity and manifold symptoms, diagnosis can be challenging. Optional GATA3 testing was suggested in 2018, except in cases of isolated sensorineural deafness or renal disease with pertinent family history. In isolated ‘H’ cases without ‘D’ and ‘R’, GATA3 studies are not required, as no haploinsufficiency cases were reported. Given the rise in genetic disorders, physicians should consistently consider rare genetic disorders in patients with suggestive symptoms, even decades after onset. Although diagnosis might not always impact management directly, it aids patients in accepting their condition and has broader family implications.

Learning points

• There is currently an important increase in genetic and clinical characterization of new orphan diseases and their causative agents.

• Unbiased re-evaluation for possible genetic disorders is necessary at every consultation.

• It is essential to recognize the differential diagnosis of idiopathic hypoparathyroidism.

• The patient’s clinical presentation and family history can be important to establish the correct diagnosis.

• Physicians should not hesitate to search a patient’s signs and symptoms online.

Summary

Bardet–Biedl syndrome (BBS) is a rare, autosomal recessive, multisystem non-motile ciliopathy of progressive onset. It is primarily characterised by rod–cone dystrophy, early-onset obesity and related complications, postaxial polydactyly, renal and genitourinary abnormalities, learning disabilities, and hypogonadism. The diagnosis is based on Beales’ modified diagnostic criteria. We present a case of two monozygotic female twins, 17 years of age at presentation, referred for obesity since childhood. The initial hormonal work-up was negative and no dysmorphic features were noted. They were diagnosed with exogenous obesity. However, after ophthalmologic problems became apparent, rod–cone dystrophy was observed and genetic testing was performed. A mutation in the BBS2 gene led to the diagnosis of BBS, although the full diagnostic criteria were not met. This case not only highlights the need to raise awareness for BBS but also exposes two limitations of the current diagnostic standard. The first limitation is the low sensitivity of the clinical diagnostic model, due to the progressive onset and the high variability of the syndrome. The second limitation is the unclear role of genetic testing. As genetic testing becomes more widely available, genetic diagnosis preceding clinical diagnosis will become more common, leading to a diagnostic conundrum. We propose an update of the diagnostic model. A less strict application in the presence of confirmed genetic mutations should be applied, as this could facilitate earlier diagnosis and intervention. This is important because therapeutic agents are being developed that could have a significant impact on quality of life and prognosis.

Learning points

• Due to the low prevalence, the significant inter-and intrafamilial variation, and the slowly evolving phenotype, monogenic forms of obesity such as Bardet–Biedl syndrome are difficult to diagnose. Despite advances in the understanding of the presentation, pathophysiology and access to accurate genetic characterisation, a substantial number of diagnoses are still made by ophthalmology, as recognition of BBS in other departments of medicine, remains limited.

• Clinical diagnosis of BBS is based on Beales’ modified diagnostic criteria which require the presence of four primary features or three primary features plus two secondary features. This model has its limitations. Due to the progressive onset of clinical symptoms, patients generally do not meet the diagnostic criteria early in life, leading to a delay in diagnosis. In addition, the role of genetic testing remains controversial. However, as it becomes more widely available, genetic diagnosis may precede a full clinical diagnosis.

• BBS has an impact on the quality of life and prognosis of both the patient and the family. Obesity management strategies are an important part of the multidisciplinary approach, as there is no cure available. Setmelanotide has shown promising results in a phase 3 trial, but its effect in clinical practice remains unproven.