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

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.

Summary

A male phenotype accompanied by a 45,X karyotype is rare. It may occur due to Y chromosomal translocation or insertion to X/autosome. Clinical presentation may vary depending on the presence of the Y chromosomal locus and the degree of loss of autosome material. 45,X males can present with short stature and Turner syndrome phenotype due to haploinsufficiency of genes which are normally expressed in both X and Y chromosomes. The presence of the sex-determining region Y (SRY) gene leads to the differentiation of bipotential gonads to testis. Most individuals go through puberty normally, but some may need pubertal induction for delayed puberty. Rarely some can have a pubertal arrest. The risk of gonadoblastoma is minimal in these individuals due to functioning testicular tissue. The azoospermia factor (AZF) region is found on the long arm of the Yq chromosome and is needed for spermatogenesis. In a 45,X male with unbalanced translocation of Y chromosome, spermatogenesis can be affected due to the lack of AZF leading to Sertoli cell-only syndrome. This will have an implication on fertility in adult life. We present a 14-year-old boy with developmental delay, learning difficulties and subtle dysmorphic features who was diagnosed with 45,X,der(2)t(Y:2)(?:p25). Fluorescence in situ hybridisation analysis revealed translocation of SRY (Yp11.3) to the terminal part of the short arm of chromosome 2 resulting in the deletion of most of the Y chromosome (Yp11.2-q12) and part of chromosome 2(2p25.3). This is the first case where SRY translocation to chromosome 2 presents with the above clinical presentation.

Learning points

• 45,X karyotype is rare in male.

• It may occur due to SRY translocation or an insertion to X/autosome.

• SRY gene translocation to chromosome 2 has been not reported in the literature.

• Clinical presentation can be varied due to degree of loss of chromosomal material.

• Due to loss of AZF region found on the long arm of the Yq, spermatogenesis can be affected. Loss of 2p25 leads to learning difficulty and obesity.

Summary

The most frequent causes of pancreatitis classically have been known to be gallstones or alcohol. However, genetics can also play a key role in predisposing patients to both chronic and acute pancreatitis. The serine protease inhibitor Kazal type 1 (SPINK 1) gene is known to be strongly associated with pancreatitis. Patients with these underlying genetic mutations can have severe diseases with a high morbidity rate and frequent hospitalization. We report an Arab girl who presented with acute pancreatitis at the age of 7 years progressing to recurrent chronic pancreatitis over a few years. She had severe obesity from the age of 4 years and developed type 2 diabetes at the age of 12. She had a normal biliary system anatomy. Genetic analysis showed that she had combined heterozygous mutations in the SPINK1 gene (SPINK1, c.101A>G p.(Asn34Ser) and SPINK1, c.56-37T>C). Her parents were first-degree cousins, but neither had obesity. Mother was detected to have the same mutations. She had type 2 diabetes but never presented with pancreatitis. This case is the first to be reported from the Arab region with these combined mutations leading to recurrent chronic pancreatitis. It illustrates the importance of diagnosing the underlying genetic mutation in the absence of other known causes of pancreatitis. Considering the absence of pancreatitis history in the mother who did not have obesity but harboured the same mutations, we point out that severe obesity might be a triggering factor of pancreatitis in the presence of the mutations in SPINK1 gene in this child. While this is not an assumption from a single patient, we show that not all carriers of this mutation develop the disease even within the same family. Triggering factors like severe obesity might have a role in developing the disease.

Learning points

• Acute recurrent pancreatitis and chronic pancreatitis are uncommon in children but might be underdiagnosed.

• Biliary tract anomalies and dyslipidaemias are known causative factors for pancreatitis, but pancreatitis can be seen in children with intact biliary system.

• Genetic diagnosis should be sought in children with pancreatitis in the absence of known underlying predisposing factors.

• SPINK1 mutations can predispose to an early-onset severe recurrent pancreatitis and acute pancreatitis.

Summary

Congenital isolated ACTH deficiency (IAD) is a rare condition characterised by low plasma ACTH and serum cortisol with normal production of other pituitary hormones. TBX19 (also known as TPIT) is a T-box pituitary restricted transcription factor important for POMC gene transcription and terminal differentiation of POMC-expressing cells. TBX19 gene mutations have been shown to cause neonatal-onset congenital IAD. We report a neonate of Romanian origin, who presented at 15 h of life with respiratory arrest and hypoglycaemia which recurred over the following 2 weeks. Biochemical investigations revealed IAD, with undetectable serum cortisol (cortisol < 1 μg/dL; normal range (NR): 7.8–26.2) and plasma ACTH levels within the normal range (22.1 pg/mL; NR: 4.7–48.8). He responded to hydrocortisone treatment. Patient DNA was analysed by a HaloPlex next-generation sequencing array targeting genes for adrenal insufficiency. A novel homozygous synonymous mutation p.Thr96= (Chr1:168260482; c.288G>A; rs376493164; allele frequency 1 × 10⁻⁵, no homozygous) was found in exon 2 of the TBX19 gene. The effect of this was assessed by an in vitro splicing assay, which revealed aberrant splicing of exon 2 giving rise to a mutant mRNA transcript whereas the WT vector spliced exon 2 normally. This was identified as the likely cause of IAD in the patient. The predicted protein product would be non-functional in keeping with the complete loss of cortisol production and early presentation in the patient.

Learning points

• Synonymous variants (a nucleotide change that does not alter protein sequence) usually thought to be benign may still have detrimental effects on RNA and protein function causing disease. Hence, they should not be ignored, especially if very rare in public databases.

• In vitro splicing assays can be employed to characterise the consequence of intronic and exonic nucleotide gene changes that may alter splicing.

• Establishing a diagnosis due to a TBX19 mutation is important as it defines a condition of isolated ACTH deficiency not associated with additional pituitary deficiencies.

Summary

We report a male infant with congenital nephrogenic diabetes insipidus (NDI) who presented with hypercalcemia and hyperphosphatemia since birth. Serum sodium started to increase at 39 days. Although there was no polyuria, urine osmolality was 71 mOsm/kg, when serum osmolality was 296 mOsm/kg with plasma arginine vasopressin 22.5 pg/mL. He was thus diagnosed as NDI. An undetectable level of urine calcium and unsuppressed intact parathyroid hormone suggested hyperparathyroidism including calcium-sensing receptor mutations that could cause hypercalcemia-induced NDI. Polyuria became apparent after the initiation of i.v. infusion for the treatment of hypernatremia. Low calcium and low sodium formula with hypotonic fluid infusion did not correct hypernatremia, hypercalcemia, or hyperphosphatemia. Hydrochlorothiazide and subsequently added celecoxib effectively decreased urine output and corrected electrolytes abnormalities. Normal serum electrolytes were maintained after the discontinuation of low calcium formula. The genetic analysis revealed a large deletion of the arginine vasopressin receptor-2 (AVPR2) gene but no pathogenic variant in the calcium-sensing receptor (CASR) gene. Whether hypercalcemia and hyperphosphatemia were caused by dehydration alone or in combination with other mechanisms remains to be clarified.

Learning points

• Congenital NDI can present with neonatal hypercalcemia and hyperphosphatemia.

• Hypercalcemia and hyperphosphatemia can be treated with low calcium and low sodium formula, hydration, hydrochlorothiazide, and celecoxib.

• Genetic testing is sometimes necessary in the differentiating diagnosis of hypercalcemia associated with NDI.

Learning points:

• Monogenic diabetes should be suspected in patients presenting with syndromic features, multisystem congenital disease, neonatal-onset diabetes and/or a suggestive family history.

• Recognition and identification of genetic diabetes may improve patient understanding and empowerment and allow for better tailored management.

• Identification of a genetic disorder may have important implications for family planning.

Learning points:

• Long-acting somatostatin analogues are effective in managing persistent CHI in BWS.

• UPD(11)pat genotype may be a pointer to persistent and severe CHI.

• Hepatoblastoma and Wilms’ tumour may have an onset within early infancy and early tumour surveillance is essential.

• Tumours associated with earlier onset may be resistant to recognised first-line chemotherapy.

Learning points

• Adult patients with X-ALD may be misdiagnosed as having multiple sclerosis or idiopathic spastic paraparesis for many years before the correct diagnosis is identified.

• Screening for X-ALD with a VLCFA panel should be strongly considered in male children with primary adrenal insufficiency and in male adults presenting with non-autoimmune primary adrenal insufficiency.

• Confirmation of a genetic diagnosis of X-ALD can be very useful for a patient's family as genetic testing enables detection of pre-symptomatic female heterozygotes who can then be offered pre-natal testing to avoid transmission of the disease to male offsprings.

Learning points

• HH is a cause of severe hypoglycaemia in the newborn period.

• Paternal mutations in ABCC8/KCNJ11 can lead to diffuse or focal disease.

• ¹⁸F-DOPA-PET/CT scan is the current imaging of choice for localising focal lesions.

• Gallium-68 tetra-aza-cyclododecane-N N′N″N-‴-tetra-acetate octreotate PET scan is not a useful imaging tool for localising focal lesions.

• The molecular mechanism by which a heterozygous ABCC8 mutation leads to diffuse disease is currently unclear.

• Focal lesions are curable by lesionectomy and so genetic studies in patients with HH must be followed by imaging using ¹⁸F-DOPA-PET/CT scan.