Long-Term Follow-up of a Case with Proprotein Convertase 1/3 Deficiency: Transient Diabetes Mellitus with Intervening Diabetic Ketoacidosis During Growth Hormone Therapy

PROPROTEIN CONVERTASE 1/3 DEFICIENCY WITH PELVIC EWING SARCOMA

Proprotein convertase 1/3 (PC 1/3) deficiency is a rare, autosomal recessive disorder caused by mutations in the PCSK1 gene. The disease is characterized by early-onset chronic diarrhea/malabsorption, followed by severe obesity and hormonal deficiencies such as hypocortisolism, hypothyroidism, diabetes insipidus, hypogonadism, growth deficiency, and diabetes mellitus. Ewing's sarcoma is a rare tumor, usually of small dimensions of neuroectodermal origin that is difficult to distinguish pathologically from a primitive neuroectodermal tumor. A 22-year-old female patient with PC 1/3 deficiency was admitted to our clinic with recurrent urinary tract infections. Magnetic resonance imaging (MRI) revealed an 11x12 cm pelvic mass displacing the uterus. A core-needle biopsy was performed on the pelvic mass. As a result of the pathological evaluation, ıt was diagnosed with pelvic Ewing's sarcoma. The patient was started on the VAC-IE chemotherapy protocol. We report a case of pelvic Ewing's sarcoma in a patient with PC 1/3 deficiency. Further research is needed to assess malignancy risk in metabolic disorders including very rare disorders like PC 1/3 deficiency.

Rare Heterozygous PCSK1 Variants in Human Obesity: The Contribution of the p.Y181H Variant and a Literature Review

Recently, it was reported that heterozygous PCSK1 variants, causing partial PC1/3 deficiency, result in a significant increased risk for obesity. This effect was almost exclusively generated by the rare p.Y181H (rs145592525, GRCh38.p13 NM_000439.5:c.541T>C) variant, which affects PC1/3 maturation but not enzymatic capacity. As most of the identified individuals with the heterozygous p.Y181H variant were of Belgian origin, we performed a follow-up study in a population of 481 children and adolescents with obesity, and 486 lean individuals. We identified three obese (0.62%) and four lean (0.82%) p.Y181H carriers (p = 0.506) through sanger sequencing and high resulting melting curve analysis, indicating no association with obesity. Haplotype analysis was performed in 13 p.Y181H carriers, 20 non-carriers (10 with obesity and 10 lean), and two p.Y181H families, and showed identical haplotypes for all heterozygous carriers (p < 0.001). Likewise, state-of-the-art literature concerning the role of rare heterozygous PCSK1 variants implies them to be rarely associated with monogenic obesity, as first-degree carrier relatives of patients with PC1/3 deficiency are mostly not reported to be obese. Furthermore, recent meta-analyses have only indicated a robust association for scarce disruptive heterozygous PCSK1 variants with obesity, while clinical significance is less or sometimes lacking for most nonsynonymous variants.

Islet MC4R Regulates PC1/3 to Improve Insulin Secretion in T2DM Mice via the cAMP and β-arrestin-1 Pathways

Melanocortin-4 receptor (MC4R) plays an important role in energy balance regulation and insulin secretion. It has been demonstrated that in the pancreas, it is expressed in islet α and β cells, wherein it is significantly correlated with insulin and glucagon-like peptide-1 (GLP-1) secretion. However, the molecular mechanism by which it regulates islet function is still unclear. Therefore, in this study, our aim was to clarify the signaling and target genes involved in the regulation of insulin and GLP-1 secretion by islet MC4R. The results obtained showed that in islet cells, the expression of prohormone convertase 1/3 (PC1/3), which is correlated with islet GLP-1 and insulin secretion, increased significantly under the action of the MC4R agonist, NDP-α-MSH, but decreased under the action of the MC4R antagonist, AgRP. Additionally, we observed that to exert their regulatory functions in the islets, cAMP and β-arrestin-1 acted as important signaling mediators of MC4R, and compared with control islets, the cAMP, PKA, and β-arrestin-1 levels corresponding to NDP-α-MSH-treated islets were significantly elevated; however, in AgRP-treated islets, their levels decreased significantly. Islets treated with the PKA inhibitor, H89, and the ERK1/2 inhibitor, PD98059, also showed significant decreases in PC1/3 expression level, indicating that the cAMP and β-arrestin-1 pathways are significantly correlated with PC1/3 expression. These findings suggest that islet MC4R possibly affects PC1/3 expression via the cAMP and β-arrestin-1 pathways to regulate GLP-1 and insulin secretion. These results provide a new theoretical basis for targeting the molecular mechanism of type 2 diabetes mellitus.

Modulation of PC1/3 activity by a rare double-site homozygous mutation

OBJECTIVES

Preprotein convertase 1/3 deficiency is a rare autosomal recessive disorder in which patients present with malabsorptive diarrhea and a series of symptoms of endocrine disorders such as polydipsia, reactive hypoglycemia, growth hormone deficiency, hypothyroidism, adrenal insufficiency, and early onset obesity. In its essence, pituitary hormone deficiency is caused by insufficient cleavage of pituitary prohormones. Here, we describe a female child with a rare double-site homozygous mutation in PCSK1 (Proprotein convertase subtilisin/kexin-type 1) gene, and thereby intend to investigate the relationship between these novel mutation sites and changes in protein synthesis and function.

METHODS

We tested this patient's blood and urine fecal indicators of infection, blood electrolytes, and relevant endocrine hormone levels in the laboratory. Next Generation Sequencing was applied to screen the patient's DNA. Western Blot was performed to evaluate the mutant protein's expression. The enzymatic activity was measured as the rate of cleavage of a synthetic fluorogenic substrate in a specific solution.

RESULTS

We found that this patient presented shortly after birth with uncorrectable diarrhea and symptoms of metabolic acidosis with hypothyroidism. Next Generation Sequencing revealed that a rare double-site homozygous missense mutation, c.763G > A (p.G255R) and c.758C > T (p.S253L), were detected in exon 7 of PCSK1 (Proprotein convertase subtilisin/kexin-type 1) gene on chromosome 5 of the patient. Western blotting revealed that there was no significant decrease in protein synthesis levels in the mutant phenotype compared to the wild type. Compared with WT type, the proteins expressed by the mutations showed a significant decrease in the enzyme activity towards the fluorescent substrates. However, neither the single site mutation p.S253L or p.G255R, nor the double-site mutation of both, all showed no significant differences from each other.

CONCLUSIONS

These two missense mutations have not been reported before, and it is even rarer to find homozygous variation of two sites in one patient. This study identifies two novel mutations for the first time and further investigates the changes in protein synthesis and enzyme activity, providing a new pathway to continue to explore the pathogenesis of diseases associated with the function of PC1/3.

A novel mutation of PCSK1 responsible for PC1/3 deficiency in two siblings

Proprotein convertase 1 (PCSK1, PC1/3) deficiency is an uncommon cause of neonatal malabsorptive diarrhoea associated with endocrinopathies that are due to the disrupted processing of a large number of prohormones, including proinsulin. To date, only 26 cases have been reported. Herein, we describe two siblings with typical features including severe congenital diarrhoea, central diabetes insipidus, growth hormone deficiency, and hypoadrenalism. Next generation sequencing found a homozygous missense mutation in exon 5 of PCSK1 gene, c.500A>C (p.Asp167Ala), located within the catalytic domain. Both patients presented a high level of proinsulin. In the first years of life they required parenteral nutrition and hormone replacement therapy. The patients, aged 3 and 1.5 years, experienced several infectious episodes associated with septic shocks. While the mechanism underlying intestinal failure remains poorly investigated, parenteral nutrition is essential in order to ensure normal growth in early childhood.

Enteroendocrine Dysfunction in Two Saudi Sisters

Proprotein convertase (PC) deficiency is a rare autosomal recessive disorder caused by mutations in proprotein convertase subtilisin/kexin type 1 (PCSK1). It is characterized by severe malabsorptive early-onset diarrhea, obesity, and systemic endocrinopathies. Only few cases have been reported in the literature; we have add two female sisters with some difference in clinical progress. Herein, we describe two sisters with congenital osmotic diarrhea diagnosed with PC1/3 deficiency, causing malabsorptive diarrhea and enteroendocrine dysfunction, who presented with chronic enteropathy with hypernatremia but with different expressivity. PC1/3 deficiency presents with symptoms and signs that mimic glucose-galactose malabsorption. Because of the clinical paucity and heterogeneity of congenital enteropathies, whole-exome sequencing may be of great help towards early diagnosis and effective treatment.

A case of prohormone convertase deficiency diagnosed with type 2 diabetes

Prohormone convertase 1/3, encoded by the proprotein convertase subtilisin/kexin type 1 gene, is essential for processing prohormones; therefore, its deficiency is characterized by a deficiency of variable levels in all hormone systems. Although a case of postprandial hypoglycemia has been previously reported in the literature, prohormone convertase insufficiency with type 2 diabetes mellitus has not yet been reported. Our case, a 14-year-old girl, was referred due to excess weight gain. She was diagnosed as having type 2 diabetes mellitus based on laboratory test results. Prohormone convertase deficiency was considered due to the history of resistant diarrhea during the infancy period and her rapid weight gain. Proinsulin level was measured as >700 pmol/L(3.60-22) during diagnosis. In genetic analysis, a c.685G> T(p.V229F) homozygous mutation in the PCSK1 gene was detected and this has not been reported in relation to this disorder. In conclusion, patients with recurrent resistant diarrhea during infancy followed by rapid weight gain need to be evaluated with the diagnosis of prohormone convertase deficiency.

A New Case of PCSK1 Pathogenic Variant With Congenital Proprotein Convertase 1/3 Deficiency and Literature Review

ISSUE

To report a homozygous pathogenic variant in PCSK1 in a boy affected with proprotein convertase 1/3 (PC1/3) deficiency.

CASE DESCRIPTION AND LITERATURE REVIEW

A male infant born to consanguineous Turkish parents presented in the first week of life with transient central diabetes insipidus, watery diarrhea, micropenis due to hypogonadotropic hypogonadism and GH deficiency, and transient asymptomatic hypoglycemia. Further endocrine defects gradually appeared, including central hypothyroidism and mild central hypocortisolism (at 1 year), central diabetes insipidus that reappeared progressively (at 2.5 years), and obesity (at 2 years). Whole-exome sequencing revealed a homozygous nonsense pathogenic variant (NM_000439.4) c. 595 C>T in exon 5 of PCSK1, not yet reported in cases of PC1/3 deficiency. To date, 26 cases of PC1/3 deficiency have been reported in the literature. All individuals had early and severe malabsorptive diarrhea and 83% had polyuria-polydipsia syndrome (before 5 years). Most (79%) had early onset obesity. Various endocrine disorders were present, including GH deficiency (44%), mild central hypothyroidism (56%), central hypogonadism (44%), central hypocortisolism (57%), and postprandial hypoglycemia (52%). When described (n = 15), proinsulin levels were consistently high: between 8 and 154 times the upper limit of normal (mean 74).

CONCLUSION

We described a homozygous nonsense pathogenic variant (NM_000439.4) c. 595 C>T in exon 5 of PCSK1 in a boy with congenital PC1/3 deficiency. Elevated proinsulin could be useful in the diagnosis of this condition.