Identification of Three Novel and One Known Mutation in the WFS1 Gene in Four Unrelated Turkish Families: The Role of Homozygosity Mapping in the Early Diagnosis

Objective: Bi-allelic mutations in the wolframin gene (WFS1) cause Wolfram syndrome 1 (WS1 or DIDMOAD) characterized by nonautoimmune diabetes mellitus, optic atrophy, diabetes insipidus, sensorineural deafness, urinary tract abnormalities, and neuropsychiatric disorders. Patients presenting with an incomplete phenotype of WS1 were evaluated using homozygosity mapping and subsequent whole-exome sequencing. Methods: Four unrelated consanguineous Turkish families, including seven affected children, and their unaffected parents and siblings were evaluated. Homozygosity mapping was performed, followed by whole-exome sequencing of WFS1. Mutations were classified according to results of "in silico" analyses, protein prediction, and functional consequences. Results: Homozygosity mapping confirmed shared homozygous regions on chromosome 4 (chr4p16.1) between the affected individuals, that was absent in their unaffected siblings. Exome sequencing identified three novel (c.1215T>A, c.554G>A, c.1525_1540dup) and one known (c.1522_1523delTA) mutations in WFS1. All mutations were predicted to cause stop codon leading to early termination of protein synthesis and complete loss-of-function. All patients were found to be homozygous for the change, with parents and other unaffected siblings being carriers. Conclusion: Our study expands the mutation spectrum of WSF1 mutations with three novel mutations. Homozygosity mapping may provide enrichment for molecular genetic analysis and early diagnosis of WS1 patients with incomplete phenotype, particularly in consanguineous pedigrees.

A novel ALMS1 homozygous mutation in two Turkish brothers with Alström syndrome.

BACKGROUND: Alström syndrome (AS) is an extremely rare, autosomal recessive disorder characterised by multi-organ features that typically manifest within the first two decades of life. AS is caused by mutations in the Alström syndrome 1 (ALMS1) gene located at 2p13.1. METHODS: In the current study, two brothers from a first-cousin consanguineous family presented with a complex phenotype and were suspected of having AS. RESULTS: Both brothers were found to be homozygous for a novel nonsense c.7310C>A (p.S2437X) mutation in exon-8 of ALMS1 gene. The consanguineous parents were sequenced and both were heterozygous for the same mutation. CONCLUSIONS: This particular mutation has never been reported before and confirmed the diagnosis of AS in the patients. Our work identifies a novel mutation in ALMS1 gene responsible for the complex phenotype of AS in these patients.

Dipeptidyl peptidase-4 expression in pancreatic tissue from patients with congenital hyperinsulinism.

Congenital hyperinsulinism (CHI) is caused by unregulated insulin release and leads to hyperinsulinaemic-hypoglycaemia (HH). Glucagon like peptide-1 (GLP-1), glucose-dependent insulinotropic peptide (GIP), peptide YY (PYY) and the enzyme; dipeptidyl peptidase-4 (DPP-4) all regulate appetite and glucose homeostasis. These proteins have been identified as possible contributors to HH but the mechanism remains poorly understood. We aimed to look at the expression pattern of pancreatic DPP-4 in children with focal and diffuse CHI (FCHI and DCHI, respectively). Using immunohistochemistry; we determined DPP-4 expression patterns in the pancreas of CHI patients. DPP-4 was found to be expressed in the pancreatic ß, α and δ-cells in and around the focal area. However, it was predominantly co-localised with ß-cells in the paediatric tissue samples. Additionally, proliferating ß-cells expressed DPP-4 in DCHI, which was absent in the FCHI pancreas. Insulin was found to be present in the exocrine acini and duct cells of the DCHI pancreas suggestive of exocrine to endocrine transdifferentiation. Furthermore, 6 medically-unresponsive DCHI pancreatic samples showed an up-regulation of total pancreatic DPP-4 expression. In conclusion; the expression studies have shown DPP-4 to be altered in HH, however, further work is required to understand the underlying role for this enzyme.

A novel homozygous SLC19A2 mutation in a Portuguese patient with diabetes mellitus and thiamine-responsive megaloblastic anaemia.

Thiamine-responsive megaloblastic anaemia (TRMA) is a rare syndrome where patients present with early onset diabetes mellitus, megaloblastic anaemia and sensorineural deafness. This report describes a new case of TRMA syndrome in a female patient of Portuguese descent, born to unrelated parents. The patient was found to have a novel homozygous change R397X in exon 4 of the SLC19A2 gene, leading to a premature stop codon. The patient's diabetes and anaemia showed a good response to daily thiamine doses, reducing the daily insulin dose requirement. The report further indicates that TRMA is not only limited to consanguineous or ethnically isolated families, and should be considered as a differential diagnosis for patients presenting with suggestive clinical symptoms.

Familial isolated growth hormone deficiency due to a novel homozygous missense mutation in the growth hormone releasing hormone receptor gene: clinical presentation with hypoglycemia.

CONTEXT: Mutations in the growth hormone releasing hormone receptor (GHRHR) gene are a relatively rare cause of isolated growth hormone deficiency (IGHD). OBJECTIVE: This study aimed to understand the biochemical basis of hypoglycemia in the index case and the molecular basis of severe short stature in a large consanguineous family with IGHD. PATIENTS AND METHODS: The index case presented with a hypoglycemic convulsion, following which eight members in two related consanguineous Turkish families were identified with IGHD. Homozygosity mapping identified the homozygous regions shared only among the affected individuals. Sanger sequencing of GHRHR, which resided in the shared homozygous region, was performed. In silico analysis of the pathogenic GHRHR variant was performed. RESULTS: The clinical presentation and hormonal analysis confirmed GH deficiency in all affected individuals. Magnetic resonance imaging scan of the pituitary gland showed anterior pituitary hypoplasia in five affected individuals in which the youngest was only 0.4 years old, but with normal pituitary size in three affected individuals. Homozygosity mapping showed two large homozygous regions on chromosome 7 shared only among affected individuals. Sanger sequencing of GHRHR gene present in one of these shared regions identified a novel homozygous missense mutation (p.C64G) segregating with the disease phenotype. In silico analysis predicted the mutation to be deleterious and disease causing. CONCLUSIONS: We describe a large consanguineous Turkish kindred with IGHD due to a novel homozygous missense GHRHR mutation. This is the first description of presentation with hypoglycemia and the earliest reported occurrence of anterior pituitary hypoplasia in patients with GHRHR mutation.