Imerslund-Gräsbeck syndrome in a 25-month-old Italian girl caused by a homozygous mutation in AMN

Imerslund-Gräsbeck syndrome: a comprehensive review of reported cases

Imerslund-Gräsbeck syndrome (IGS) is a rare autosomal recessive disorder characterized by vitamin B12 malabsorption. Most patients present with non-specific symptoms attributed to vitamin B12 deficiency, and proteinuria. Patients may if untreated, develop severe neurocognitive manifestations. If recognized and treated with sufficient doses of vitamin B12, patients recover completely. We provide, for the first time, an overview of all previously reported cases of IGS. In addition, we provide a complete review of IGS and describe two new patients.

Clinical, phenotypic and genetic landscape of case reports with genetically proven inherited disorders of vitamin B12 metabolism: A meta-analysis

Inherited disorders of B₁₂ metabolism produce a broad spectrum of manifestations, with limited knowledge of the influence of age and the function of related genes. We report a meta-analysis on 824 patients with a genetically proven diagnosis of an inherited disorder of vitamin B₁₂ metabolism. Gene clusters and age categories are associated with patients' manifestations. The "cytoplasmic transport" cluster is associated with neurological and ophthalmological manifestations, the "mitochondrion" cluster with hypotonia, acute metabolic decompensation, and death, and the "B₁₂ availability" and "remethylation" clusters with anemia and cytopenia. Hypotonia, EEG abnormalities, nystagmus, and strabismus are predominant in the younger patients, while neurological manifestations, such as walking difficulties, peripheral neuropathy, pyramidal syndrome, cerebral atrophy, psychiatric disorders, and thromboembolic manifestations, are predominant in the older patients. These results should prompt systematic checking of markers of vitamin B₁₂ status, including homocysteine and methylmalonic acid, when usual causes of these manifestations are discarded in adult patients.

Acute cerebellar ataxia as the first manifestation of Imerslund-Gräsbeck syndrome

Imerslund-Gräsbeck syndrome is a rare condition caused by vitamin B12 deficiency and proteinuria. In this article, we reported the case of a 10-year-old girl with imbalance and urinary incontinence. The case had cerebellar ataxia as the primary manifestation. The disequilibrium had progressed gradually within three weeks and was consistent with the symptoms of cerebellar involvement and urinary incontinence. Brain and cervico-thoraco-lumbar magnetic resonance imaging were normal. The patient had elevated lactate dehydrogenase (LDH=4775), in addition to macrocytic anemia, on laboratory examinations; thus, the possibility of malignancy was raised. Then, bone marrow aspiration was performed, showing hypercellular marrow with megaloblastic changes. This finding proved megaloblastic anemia. Regarding the low prevalence of vitamin B12 deficiency in healthy individuals, extensive studies were performed to find out the cause. The serum level of vitamin B12 was found to be lower than the normal range. Although urinalysis revealed significant proteinuria, further nephrological investigations did not indicate any abnormalities. No evidence of serious problems was observed in the gastrointestinal tract study, and metabolic studies were normal. Finally, based on the obtained data, Imerslund-Gräsbeck syndrome was recognized. Patient was treated by vitamin B12 injection, leading to improved balance, and in one-month follow-up, she was able to walk independently, and the cerebellar symptoms had greatly disappeared; however, proteinuria persisted.

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.

Prospective long-term evaluation of parenteral hydroxocobalamin supplementation in juvenile beagles with selective intestinal cobalamin malabsorption (Imerslund-Gräsbeck syndrome)

BACKGROUND

Prospective studies on maintenance treatment for Beagles with hereditary selective cobalamin (Cbl) malabsorption (Imerslund-Gräsbeck syndrome, IGS) are lacking. In our experience, measurement of methylmalonic acid (MMA), a Cbl-dependent metabolite, seems more helpful to monitor Cbl status as compared with serum Cbl concentrations.

OBJECTIVES

To evaluate a standardized Cbl supplementation scheme in Beagles with IGS. We hypothesized that a single parenteral dose of 1 mg hydroxocobalamin (OH-Cbl) would maintain clinical and metabolic remission for up to 2 months.

ANIMALS

Six client-owned juvenile Beagles with genetically confirmed IGS and 28 healthy control dogs.

METHODS

Prospective study. Monthly IM OH-Cbl (1 mg) supplementation was done over a median of 9 months (range, 6-13) in 6 dogs, followed by bimonthly (every 2 months) injections in 5 dogs over a median of 6 months (range, 3-10). Health status was assessed by routine clinical examinations at injection time points and owner observations. Voided urine samples were collected immediately before OH-Cbl injections for measurement of MMA-to-creatinine concentrations using a gas-liquid chromatography-tandem mass spectrometry (GC-MS) method.

RESULTS

All dogs were clinically healthy while receiving monthly and bimonthly OH-Cbl supplementation. Urinary MMA results in healthy dogs ranged from 1.3 to 76.5 mmol/mol creatinine (median, 2.9). Median urinary MMA concentrations did not differ between dogs with IGS receiving monthly (n = 49; 5.3 mmol/mol creatinine; range, 2.3-50.4) and bimonthly (n = 31; 5.3 mmol/mol creatinine; range, 1.6-50) injections.

CONCLUSIONS AND CLINICAL IMPORTANCE

A maintenance parenteral dose of 1 mg OH-Cbl monthly or bimonthly appears adequate in Beagles with IGS monitored by metabolic testing.