Imerslund-Gräsbeck syndrome in a child with a novel compound heterozygous mutations in the AMN gene: a case report.

BACKGROUND: Imerslund-Gräsbeck syndrome (IGS) is an autosomal recessive disorder characterized by selective vitamin B12 malabsorption, resulting in vitamin B12 deficiency and impaired reabsorption of proximal tubular proteins.This case highlights a previously unidentified compound heterozygous variant in the Amnionless (AMN) gene that causes IGS syndrome and underscores the importance of long-term oral vitamin B12 replacement therapy in managing the condition. CASE PRESENTATION: In this retrospective analysis, we present the clinical data of a 3-year and 6-month-old female child diagnosed with IGS at Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology, China, in November 2018. The child was admitted to the hospital due to a history of anemia persisting for over a month. There was no previous significant medical history. The admission examination revealed megaloblastic anemia with proteinuria. Serum vitamin B12 levels were decreased, while folic acid and renal function were normal. The patient was diagnosed with megaloblastic anemia and started long-term oral vitamin B12 replacement therapy. Throughout the follow-up period, blood tests consistently showed normal results, while proteinuria persisted. In November 2019, the child and her parents underwent whole exome sequencing analysis, which revealed a novel compound heterozygous variant in the AMN gene: c.162 + 1G > A and c.922 C > T (p.Q308X) in the child, c.162 + 1G > A in the father, and c.922 C > T (p.Q308X) in the mother. Therefore, this child was further diagnosed with IGS. CONCLUSIONS: In this case, whole exome sequencing proves to be highly practical in daily healthcare for diagnosing and refining rare or ultra-rare diseases with ambiguous phenotypes or genetic diversity. It is also valuable for prognostic evaluation and personalized management. Additionally, the oral vitamin B12 treatment demonstrated positive clinical effects for the child, offering a new option for patients unable to undergo intramuscular vitamin B12 replacement therapy.

Severe pancytopenia at the presentation of Imerslund-Gräsbeck syndrome in a 23-month-old Italian boy.

BACKGROUND: Imerslund-Gräsbeck syndrome (IGS) is a rare autosomal recessive disorder characterized by megaloblastic anemia due to selective cobalamin malabsorption and benign proteinuria. IGS is caused by a disfunction of the cubam receptor, which mediates the reabsorption of cobalamin in the ileum and the reuptake of albumin in renal proximal tubules. CASE PRESENTATION: We describe the case of a 23-month-old-italian infant presenting with severe pancytopenia and failure to thrive in whom the diagnosis of IGS was made and vitamin B12 replacement therapy was resolutive. Genetic analysis (NGS with CNV analysis including 214 genes involved in bone marrow failure and anemia), showed the presence of two pathogenetic variants in the AMN gene (c-208-2 A > G and c.1006 + 34_1007-31del). These variants have been previously described in the literature, but their combination has never been reported. CONCLUSIONS: Imerslund-Gräsbeck syndrome should be considered in the differential diagnosis of children with severe pancytopenia even in those without neurological involvement. This case emphasizes the importance of an early diagnosis and prompt treatment, to prevent irreversible neurological injury.

[Bibliometric visualization analysis of thiamine-responsive megaloblastic anemia syndrome].

Visual analysis of the current status, research hotspots, evolving trends, and future prospects in the field of thiamine-responsive megaloblastic anemia syndrome (TRMA), providing new insights and directions for subsequent research on the pathogenic mechanisms and prevention strategies of TRMA. Taking the core database of Web of Science as the literature source, selecting TRMA-related literature records published from 1997 to 2023 as the research object, and using R software and Citexs database to conduct visual analysis and discussion of the research content. The results showed that a total of 89 publications related to the topic were published from 1997 to 2023, with an average annual publication volume of 3 papers. Classified by country, it was found that the United States, and Israel among other countries and institutions, published a significant number of papers. Through keyword frequency analysis, high frequencies of keywords such as diabetes, deafness, thiamine-responsive megaloblastic anemia, and mutations in the solute carrier family 19 member 2 (SLC19A2) gene were observed, indicating that to date, these keywords have been the main research directions, highlighting a gradually reached consensus on the mechanism exploration of TRMA. In conclusion, TRMA research focuses on the mechanisms of hot topics such as diabetes, deafness, and thiamine-responsive megaloblastic anemia, and the core gene SLC19A2 research may currently become a new breakthrough point for future molecular studies.

Transcobalamin deficiency - a rare genetic defect in transportation of cobalamin; case report.

BACKGROUND: Vitamin B12 is primarily transported from plasma to cells by Transcobalamin. Deficiency of Transcobalamin is a rare autosomal recessive disorder that results in unavailability of cobalamin in cells and accumulation of homocysteine and methylmalonic acid. CASE REPORT: We report a case of a 2-year-old male child with persistent pancytopenia, recurrent infections, and megaloblastic anemia. Next-generation sequencing identified a novel variant in exon 8 of TCN2 gene. Substantial improvement has been observed following administration of high doses of parenteral methylcobalamin. CONCLUSION: In patients with unresolved pancytopenia and megaloblastic anemia, Transcobalamin deficiency should be investigated and treated promptly to prevent any irreversible and harmful outcome.

Thiamine-responsive megaloblastic anaemia.

We report a 26-year-old girl who was diagnosed with diabetes mellitus in her childhood and was treated with insulin. With a history of visual disturbances during her childhood and anaemia, which was partially evaluated; the possibility of syndromic diabetes was considered. Genetic analysis was done and revealed a mutation in the SLC19A2 gene, confirming the diagnosis of thiamine-responsive megaloblastic anaemia. She was supplemented with thiamine, which dramatically improved her haemoglobin levels and glucose control. However, her vision could not be salvaged as the rod-cone dystrophy is a permanent damage.

Diabetes Out-of-the-Box: Diabetes Mellitus and Impairment in Hearing and Vision.

PURPOSEOF REVIEW: This review aims to provide an update on the etiologies of diabetes that are due to genetic disorders and that co-occur with impaired hearing or vision and to compare them. The potential mechanisms, including novel treatments, will be detailed. RECENT FINDINGS: Wolfram syndrome, Kearns-Sayre syndrome, thiamine-responsive megaloblastic anemia, and maternally inherited diabetes and deafness are genetic disorders characterized by diabetes, impaired hearing, and vision. They differ in mode of inheritance, age at presentation, and the involvement of other organs; they are often misdiagnosed as type 1 or type 2 diabetes. Suspicion of a genetic diabetes syndrome should be raised when pancreatic autoantibodies are negative, other organs are involved, and family history includes diabetes. Correct diagnosis of the various syndromes is important for tailoring the most advanced treatment, preventing disease progression, and enabling proper genetic counseling.

Whole-Exome Sequencing Revealed a Pathogenic Nonsense Variant in the SLC19A2 Gene in an Iranian Family with Thiamine-Responsive Megaloblastic Anemia.

OBJECTIVE: Solute carrier family 19 member 2 (SLC19A2, OMIM *603941) encodes thiamine human transporter 1 (THTR-1), which contributes to bringing thiamine (vitamin B1) into cells. Mutations in SLC19A2 lead to a rare recessive genetic disorder termed thiamine-responsive megaloblastic anemia (TRMA) syndrome. METHODS: An Iranian family with TRMA was investigated by whole-exome sequencing (WES) to determine the genetic cause(s) of the disease. Accordingly, SLC19A2 genetic variants were gathered through literature analysis. RESULTS: WES recognized a known pathogenic variant, c.697C > T (p. Q233X), within exon 2 of SLC19A2 (NM_006996). Subsequently, the proband's parents and sister were confirmed as heterozygous carriers of the identified variant. CONCLUSION: The diagnostic utility and affordability of WES were confirmed as the first approach for the genetic testing of TRMA to verify the diagnosis. This analysis can be used to guide future prenatal diagnoses and determine the consequences in the other family members.

Vitamin B12 absorption and malabsorption.

Vitamin B12 is assimilated and transported by complex mechanisms that involve three transport proteins, intrinsic factor (IF), haptocorrin (HC) and transcobalamin (TC) and their respective membrane receptors. Vitamin deficiency is mainly due to inadequate dietary intake in vegans, and B12 malabsorption is related to digestive diseases. This review explores the physiology of vitamin B12 absorption and the mechanisms and diseases that produce malabsorption. In the stomach, B12 is released from food carrier proteins and binds to HC. The degradation of HC by pancreatic proteases and the pH change trigger the transfer of B12 to IF in the duodenum. Cubilin and amnionless are the two components of the receptor that mediates the uptake of B12 in the distal ileum. Part of liver B12 is excreted in bile, and undergoes an enterohepatic circulation. The main causes of B12 malabsorption include inherited disorders (Intrinsic factor deficiency, Imerslund-Gräsbeck disease, Addison's pernicious anemia, obesity, bariatric surgery and gastrectomies. Other causes include pancreatic insufficiency, obstructive Jaundice, tropical sprue and celiac disease, bacterial overgrowth, parasitic infestations, Zollinger-Ellison syndrome, inflammatory bowel diseases, chronic radiation enteritis of the distal ileum and short bowel. The assessment of B12 deficit is recommended in the follow-up of subjects with bariatric surgery. The genetic causes of B12 malabsorption are probably underestimated in adult cases with B12 deficit. Despite its high prevalence in the general population and in the elderly, B12 malabsorption cannot be anymore assessed by the Schilling test, pointing out the urgent need for an equivalent reliable test.

Leber congenital amaurosis as an initial manifestation in a Chinese patient with thiamine-responsive megaloblastic anemia syndrome.

Thiamine-responsive megaloblastic anemia syndrome (TRMA) is an autosomal recessive disorder, inherited by the defective SLC19A2 gene that encodes a high-affinity thiamine transporter (THTR-1). TRMA is characterized by the occurrence of classical triad manifestations including megaloblastic anemia, diabetes mellitus, and sensorineural deafness. In addition to the systemic manifestations, ophthalmic features can be present and include retinitis pigmentosa, optic atrophy, cone-rod dystrophy, maculopathy, and Leber congenital amaurosis. Here we report a 6-year-old boy presenting severe early-onset retinal dystrophy with the initial diagnosis of Leber congenital amaurosis, which followed for 12 years. Diabetes mellitus occurred 3 years after vision problem. Eosinophilic granuloma of the left scapula was confirmed at 13 years old. Whole-exome sequencing was performed to identify two novel compound heterozygous variants c.725dupC (p.Ala243Serfs*3) and c.121G>A (p.Gly41Ser) in SLC19A2 gene (NM_006996.3). Oral thiamine supplementation treatment was initiated at 13 years. This case demonstrates Leber congenital amaurosis can present as the first clinical feature before systemic manifestations. Phenotypic variety should be aware and multidisciplinary teamwork and regular follow-up are important for TRMA patient care.

A 17-Month-old Boy With Pancytopenia Caused by a Rare Genetic Defect of Vitamin B12 Malabsorption.

Imerslund-Gräsbeck syndrome is an autosomal recessive disorder of vitamin B12 malabsorption presenting with megaloblastic anemia and mild proteinuria in childhood. The disorder is caused by biallelic pathogenic variants in the CUBN or AMN genes, which encode proteins involved in B12 absorption. We present the case of a 17-month-old boy with failure to thrive, pancytopenia, and fevers. His megaloblastic anemia was overlooked leading to unnecessary invasive testing. Findings on bone marrow biopsy prompted investigation for genetic disorders of B12 metabolism. Exome sequencing uncovered 1 known pathogenic variant and 1 novel likely pathogenic variant in CUBN, confirming the diagnosis of Imerslund-Gräsbeck syndrome.

[Clinical analysis of two brothers with Imerslund-Gräsbeck syndrome].

The clinical data of two children with Imerslund-Gräsbeck syndrome (IGS) who were admitted to the First Affiliated Hospital of Zhengzhou University in August 2019 was analyzed retrospectively. The two cases were siblings, aged 8 years and 8 months and 6 years and 2 months, respectively. These two boys had megaloblastic anemia, low level of vitamin B12, hyperhomocysteinemia, accompanied by proteinuria and renal tubular injury, while they showed normal folate level and renal function. Blood tandem mass spectrometry and urine organic acid analysis suggested methylmalonic acidemia (MMA). The initial diagnosis was MMA with homocysteinemia. No known pathogenic gene mutation related to MMA was found by gene sequencing. Compound heterozygous variants of amnionless (AMN) gene were detected: c.43+5G>A and c.C717G. The corrected diagnosis was IGS. Both brothers were treated with long-term intramuscular injection of vitamin B12. After follow-up for one year, these two cases had no clinical symptoms, and their blood indicators remained normal, but proteinuria and renal tubular injury persisted. Blood tandem mass spectrometry and urine organic acid analysis alone may easily lead to misdiagnosis, but combined with genetic testing can improve the accuracy of diagnosis of IGS. Lifelong parenteral vitamin B12 replacement therapy can effectively reverse the clinical and biochemical results, but is uncertain in alleviating albuminuria and renal tubule injury. It's necessary to monitor the renal function regularly.

The Effects of Genetic Mutations and Drugs on the Activity of the Thiamine Transporter, SLC19A2.

A rare cause of megaloblastic anemia (MA) is thiamine-responsive megaloblastic anemia (TRMA), a genetic disorder caused by mutations in SLC19A2 (encoding THTR1), a thiamine transporter. The study objectives were to (1) functionally characterize selected TRMA-associated SLC19A2 variants and (2) determine whether current prescription drugs associated with drug-induced MA (DIMA) may act via inhibition of SLC19A2. Functional characterization of selected SLC19A2 variants was performed by confocal microscopy and isotopic uptake studies of [3H]-thiamine in HEK293 cells. Sixty-three drugs associated with DIMA were screened for SLC19A2 inhibition in isotopic uptake studies. Three previously uncharacterized SLC19A2 variants identified in TRMA patients exhibited disrupted localization to the plasma membrane along with near-complete loss-of-function. Ten of 63 drugs inhibited SLC19A2-mediated thiamine transport ≥ 50% at screening concentrations; however, with the exception of erythromycin, none was predicted to inhibit SLC19A2 at clinically relevant unbound plasma concentrations. Data from electronic health records revealed reduced levels of thiamine pyrophosphate (TPP) in patients prescribed erythromycin, consistent with inhibition of SLC19A2-mediated thiamine transport. Here, we confirmed the role of three SLC19A2 variants in TRMA pathology. Additionally, we report that inhibition of SLC19A2 is a potential, but uncommon mechanism for DIMA.

Identification of novel compound heterozygous variants in SLC19A2 and the genotype-phenotype associations in thiamine-responsive megaloblastic anemia.

BACKGROUND AND AIMS: Thiamine-responsive megaloblastic anemia (TRMA), caused by SLC19A2 loss-of-function variants, is characterized by the triad of megaloblastic anemia, progressive sensorineural deafness, and non-type 1 diabetes mellitus. Here, we present the case of a Chinese infant with two novel variants segregating in compound heterozygous form in SLC19A2 and reviewed genotype-phenotype associations (GPAs) in patients with TRMA. MATERIALS AND METHODS: Whole-exome sequencing was performed to establish a genetic diagnosis. The clinical manifestations and genetic variants were collected by performing a literature review. The bioinformatics software SIFT, PolyPhen2, and Mutation Taster was applied to predict variant effects and analyze GPAs. RESULTS: Two novel variants segregating in compound heterozygous form in SLC19A2 (NM_006996.2: exon2:c.336_363del:p.W112fs; exon2:c.358G>T:p.G120X) was identified. Thiamine supplementation corrected anemia and diabetes mellitus but did not improve the hearing defect. In the literature, 183 patients with TRMA with 74 variants in SLC19A2 have been reported, with high incidence in the Middle East, South Asia, and the northern Mediterranean. Patients with biallelic premature termination codon variants presented with more severe phenotypes, and truncating sites on extracellular domains was a protective factor for the hemoglobin level at diagnosis. CONCLUSION: Two novel compound heterozygous variants (NM_006996.2: exon2:c.336_363del:p.W112fs; exon2:c.358G>T:p.G120X) were identified, and GPAs in TRMA indicated the predictability of clinical manifestations.

Clinical and molecular characteristics of imerslund-gräsbeck syndrome: First report of a novel Frameshift variant in Exon 11 of AMN gene.

INTRODUCTION: Imerslund-Gräsbeck syndrome (IGS) is a rare autosomal-recessive disorder characterized by selective vitamin B12 malabsorption, megaloblastic anemia, and proteinuria. The precise incidence of this disorder is unknown in the Middle East and Arab countries. The disease is caused by a homozygous variant in either AMN or CUBN genes. In addition, some compound heterozygous variants are reported. METHODS: Clinical and laboratory data of patients diagnosed with IGS in Oman were retrospectively collected. Mutation analysis for all genes involved in vitamin B12/folic acid metabolism and megaloblastic anemia was conducted using next-generation sequencing (NGS). RESULTS: Three siblings (2 girls and a boy) have been diagnosed with the condition. They exhibit a phenotypic variability with different age of presentation and different spectrum of disease. All patients harbor a novel biallelic frameshift mutation in exon 11 of AMN gene (p.Pro409Glyfs*), which was not reported previously in the literature. Both parents are heterozygotes for the same variant. All patients responded well to vitamin B12 parenteral therapy, but proteinuria persisted. CONCLUSION: In communities with high incidence of consanguinity, cases of early-onset vitamin B12 deficiency should be thoroughly investigated to explore the possibility of Imerslund-Gräsbeck syndrome and other vitamin B12-related hereditary disorders. Further local and regional studies are highly recommended.

Novel CUBN Mutation in a Young Child With Megaloblastic Anemia.

Inherited disorders of cobalamin (Cbl, vitamin B12) metabolism are rare causes of megaloblastic anemia and neurologic abnormalities. More prevalent in certain ethnic groups, these disorders occur despite adequate Cbl intake and usually result from abnormal vitamin cell transport or processing. Cubilin (CUBN, intrinsic factor-cobalamin receptor) is the intestinal receptor for the endocytosis of intrinsic factor-vitamin B12. Its gene is localized to chromosome 10p13 and mutations involving CUBN have been described in patients with congenital megaloblastic anemia. In this report, we describe a novel CUBN pathogenic variant in a child with megaloblastic anemia.

A clinical and experimental study of adult hereditary spherocytosis in the Chinese population.

Hereditary spherocytosis (HS) is often misdiagnosed due to lack of specific diagnostic methods. Our study summarized clinical characteristics and described the diagnostic workflow for mild and moderate HS in Chinese individuals, using data from 20 adults, 8 of whom presented a familial history for HS. We used scanning electron microscopy (SEM) to diagnose HS. We observed reduced eosin maleimide fluorescence activity (5.50 mean channel fluorescence (MCF) units) in the 10 cases of HS, which differed significantly when compared with 10 normal adults (15.50 units), iron deficiency anemia (15.50 MCF units), and megaloblastic anemia (12.00 MCF units) values (P < .05). Next generation sequencing results revealed that 9 out of 10 patients were found to have mutations in the spectrin alpha chain (SPTB), anchor protein (ANK1), and SLC4A1 genes. These mutations were not reported in the Human Gene Mutation Database (HGMD), 1000 human genome, ExAC, and dbSNP147 databases. Splenectomy proved to be beneficial in alleviating HS symptoms in 10 cases. It was found that for the diagnosis of HS, SEM and next generation gene sequencing method proved to be more ideal than red blood cell membrane protein analysis using sodium dodecyl sulfate polyacrylamide gel electrophoresis and western blotting.

Imerslund-Gräsbeck Syndrome presenting with microangiopathic hemolytic anemia in a child.

Imerslund-Gräsbeck Syndrome is a rare autosomal recessive disorder characterized by proteinuria and selective malabsorption of cobalamin. Deficiency of cobalamin can lead to megaloblastic anemia, pancytopenia and even "pseudo"-thrombotic microangiopathy (TMA). Signs of mechanical hemolysis on peripheral blood smear, elevated lactate dehydrogenase and thrombocytopenia are common findings of TMA. We report a child presenting with TMA features with cobalamin deficiency. Because of her family history of vitamin B12 deficiency and proteinuria, the performed genetic analysis revealed that an Imerslund-Gräsbeck Syndrome with the detection of a homozygous mutation in AMN gene.