Cystic fibrosis and fat malabsorption: Pathophysiology of the cystic fibrosis gastrointestinal tract and the impact of highly effective CFTR modulator therapy.

Cystic fibrosis (CF) is a progressive, genetic, multi-organ disease affecting the respiratory, digestive, endocrine, and reproductive systems. CF can affect any aspect of the gastrointestinal (GI) tract, including the esophagus, stomach, small intestine, colon, pancreas, liver, and gall bladder. GI pathophysiology associated with CF results from CF membrane conductance regulator (CFTR) dysfunction. The majority of people with CF (pwCF) experience exocrine pancreatic insufficiency resulting in malabsorption of nutrients and malnutrition. Additionally, other factors can cause or worsen fat malabsorption, including the potential for short gut syndrome with a history of meconium ileus, hepatobiliary diseases, and disrupted intraluminal factors, such as inadequate bile salts, abnormal pH, intestinal microbiome changes, and small intestinal bacterial overgrowth. Signs and symptoms associated with fat malabsorption, such as abdominal pain, bloating, malodorous flatus, gastroesophageal reflux, nausea, anorexia, steatorrhea, constipation, and distal intestinal obstruction syndrome, are seen in pwCF despite the use of pancreatic enzyme replacement therapy. Given the association of poor nutrition status with lung function decline and increased mortality, aggressive nutrition support is essential in CF care to optimize growth in children and to achieve and maintain a healthy body mass index in adults. The introduction of highly effective CFTR modulator therapy and other advances in CF care have profoundly changed the course of CF management. However, GI symptoms in some pwCF may persist. The use of current knowledge of the pathophysiology of the CF GI tract as well as appropriate, individualized management of GI symptoms continue to be integral components of care for pwCF.

[Subcutaneous administration of levothyroxine in refractory hypothyroidism]. / Administración subcutánea de levotiroxina en hipotiroidismo refractario.

Hypothyroidism can usually be treated effectively with oral levothyroxine (LT-4) supplementation. However, hypothyroidism refractory to treatment with LT-4 is a common clinical condition. Causes include poor compliance, interactions with food or other medications, and gastrointestinal diseases, such as inflammatory bowel disease and short bowel syndromes. Increasing the oral dose of LT-4 is not always effective in these scenarios. Therefore, other routes of administration may be necessary. In this report, we evaluate alternative treatment modalities for refractory hypothyroidism and present two patients with intestinal malabsorption successfully treated by subcutaneous administration of LT-4.

El hipotiroidismo generalmente se puede tratar de manera efectiva con levotiroxina (LT-4) oral. Sin embargo, el hipotiroidismo refractario al tratamiento con LT-4 es una condición clínica frecuente. Entre las causas se encuentra la falta de adherencia, interacciones con alimentos u otros medicamentos y enfermedades gastrointestinales, como enfermedad inflamatoria intestinal y síndromes de intestino corto. El aumento de la dosis oral de LT-4 no siempre es eficaz en estos escenarios. Por lo tanto, pueden ser necesarias otras vías de administración. En este reporte, evaluamos modalidades alternativas de tratamiento para el hipotiroidismo refractario y presentamos dos pacientes con malabsorción intestinal tratadas con éxito mediante la administración subcutánea de LT-4.

Cell differentiation is disrupted by MYO5B loss through Wnt/Notch imbalance.

Functional loss of myosin Vb (MYO5B) induces a variety of deficits in intestinal epithelial cell function and causes a congenital diarrheal disorder, microvillus inclusion disease (MVID). The impact of MYO5B loss on differentiated cell lineage choice has not been investigated. We quantified the populations of differentiated epithelial cells in tamoxifen-induced, epithelial cell-specific MYO5B-knockout (VilCreERT2 Myo5bfl/fl) mice utilizing digital image analysis. Consistent with our RNA-sequencing data, MYO5B loss induced a reduction in tuft cells in vivo and in organoid cultures. Paneth cells were significantly increased by MYO5B deficiency along with expansion of the progenitor cell zone. We further investigated the effect of lysophosphatidic acid (LPA) signaling on epithelial cell differentiation. Intraperitoneal LPA significantly increased tuft cell populations in both control and MYO5B-knockout mice. Transcripts for Wnt ligands were significantly downregulated by MYO5B loss in intestinal epithelial cells, whereas Notch signaling molecules were unchanged. Additionally, treatment with the Notch inhibitor dibenzazepine (DBZ) restored the populations of secretory cells, suggesting that the Notch pathway is maintained in MYO5B-deficient intestine. MYO5B loss likely impairs progenitor cell differentiation in the small intestine in vivo and in vitro, partially mediated by Wnt/Notch imbalance. Notch inhibition and/or LPA treatment may represent an effective therapeutic approach for treatment of MVID.

L-T4 Therapy in Enteric Malabsorptive Disorders.

Levothyroxine (L-T4) absorption can be impaired by various causes: a) L-T4 ingestion during breakfast, or with food; b) conditions of reduced gastric acidity; c) intestinal procedures and diseases such as bariatric surgery, lactose intolerance (LI), celiac disease (CD), inflammatory bowel disease; d) drugs that alter L-T4 absorption, increasing the gastric pH, or preventing the dissolution of tablets. The development of new oral formulations, i.e. the liquid preparation and the soft gel capsule, represents the most recent advance regarding L-T4 therapy. Treating hypothyroidism with L-T4 tablets can lead to an improper control of thyroid-stimulating hormone (TSH) in ~10%-15% of patients. The improperly elevated TSH is usually managed by increasing the L-T4 daily dose, and revaluating TSH upon 2-6 months. The increase of the L-T4 dosage may cause iatrogenic hyperthyroidism, especially when the underlying disorders are cured. Liquid L-T4 can be administered in patients unable to swallow capsules or tablets, and this is one of its major benefits. Liquid L-T4 can: 1- overcome food and beverages interference; 2- bypass the malabsorption associated with an increased gastric pH; 3- circumvent the issue of malabsorption in patients who underwent bariatric surgery; 4-maintain TSH values under control better than L-T4 tablets in hypothyroid patients with typical or atypical CD, or in patients with LI. Few clinical studies evaluated soft gel L-T4 with encouraging findings in patients with gastric- or coffee-related malabsorption, or hypothyroid patients without malabsorption. Additional research is necessary to investigate liquid L-T4, or soft gel capsule, in other conditions of altered L-T4 absorption.

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.

Effects of agalsidase-ß administration on vascular function and blood pressure in familial Anderson-Fabry disease.

Fabry is an X-linked disorder of glycosphingolipid metabolism that is caused by variants of the GLA gene that codes for α-galactosidase A, leading to lysosomal accumulation of globotriaosylceramide in many cell types. As a result, affected patients manifest with an increased risk of developing ischemic stroke, peripheral neuropathy, cardiac dysfunction, and chronic kidney disease. The protective effects of enzyme replacement therapy (ERT), the milestone in Fabry disease treatment, against globotriaosylceramide (GL-3) accumulation and Fabry disease progression are well known. However, the mechanism of action of ERT is not well understood. Since GL-3 also accumulates in the vascular endothelium, we investigated the effects of agalsidase-ß, a recombinant human α-Gal enzyme approved for the treatment of Fabry disease. In this study, vascular function and blood pressure in four adult siblings affected by Fabry disease were evaluated upon agalsidase-ß. In all patients, agalsidase-ß infusion improves flow-mediated dilation and augmentation index. These changes occurred after the first infusion and were then maintained for the whole period of observation, i.e., 1 year, with more pronounced additional increments in flow-mediated dilation after the second agalsidase-ß infusion. Blood pressure was also maintained at optimal levels in all of the patients for the whole period of observation. Our findings show that agalsidase-ß administration can improve vascular function in patients suffering from Fabry disease. Changes in flow-mediated dilation and augmentation index persisted for the whole period of observation (1 year), thus suggesting that early substitutive therapy should be promoted in order to protect the cardiovascular system.

The Role of Bile Acids in Chronic Diarrhea.

Bile acids (BAs) are the central signals in enterohepatic communication, and they also integrate microbiota-derived signals into enterohepatic signaling. The tissue distribution and signaling pathways activated by BAs through natural receptors, farsenoid X receptor and G protein-coupled BA receptor 1 (GPBAR1, also known as Takeda G-coupled receptor 5), have led to a greater understanding of the mechanisms and potential therapeutic agents. BA diarrhea is most commonly encountered in ileal resection or disease, in idiopathic disorders (with presentation similar to functional diarrhea or irritable bowel syndrome with diarrhea), and in association with malabsorption such as chronic pancreatitis or celiac disease. Diagnosis of BA diarrhea is based on Se-homocholic acid taurine retention, 48-hour fecal BA excretion, or serum 7αC4; the latter being a marker of hepatic BA synthesis. BA diarrhea tends to be associated with higher body mass index, increased stool weight and stool fat, and acceleration of colonic transit. Biochemical markers of increased BA synthesis or excretion are available through reference laboratories. Current treatment of BA diarrhea is based on BA sequestrants, and, in the future, it is anticipated that farsenoid X receptor agonists may also be effective. The optimal conditions for an empiric trial with BA sequestrants as a diagnostic test are still unclear. However, such therapeutic trials are widely used in clinical practice. Some national guidelines recommend definitive diagnosis of BA diarrhea over empirical trial.

Lysophosphatidic Acid Increases Maturation of Brush Borders and SGLT1 Activity in MYO5B-deficient Mice, a Model of Microvillus Inclusion Disease.

BACKGROUND & AIM: Myosin VB (MYO5B) is an essential trafficking protein for membrane recycling in gastrointestinal epithelial cells. The inactivating mutations of MYO5B cause the congenital diarrheal disease, microvillus inclusion disease (MVID). MYO5B deficiency in mice causes mislocalization of SGLT1 and NHE3, but retained apical function of CFTR, resulting in malabsorption and secretory diarrhea. Activation of lysophosphatidic acid (LPA) receptors can improve diarrhea, but the effect of LPA on MVID symptoms is unclear. We investigated whether LPA administration can reduce the epithelial deficits in MYO5B-knockout mice. METHODS: Studies were conducted with tamoxifen-induced, intestine-specific knockout of MYO5B (VilCreERT2;Myo5bflox/flox) and littermate controls. Mice were given LPA, an LPAR2 agonist (GRI977143), or vehicle for 4 days after a single injection of tamoxifen. Apical SGLT1 and CFTR activities were measured in Üssing chambers. Intestinal tissues were collected, and localization of membrane transporters was evaluated by immunofluorescence analysis in tissue sections and enteroids. RNA sequencing and enrichment analysis were performed with isolated jejunal epithelial cells. RESULTS: Daily administration of LPA reduced villus blunting, frequency of multivesicular bodies, and levels of cathepsins in intestinal tissues of MYO5B-knockout mice compared with vehicle administration. LPA partially restored the brush border height and the localization of SGLT1 and NHE3 in small intestine of MYO5B-knockout mice and enteroids. The SGLT1-dependent short-circuit current was increased and abnormal CFTR activities were decreased in jejunum from MYO5B-knockout mice given LPA compared with vehicle. CONCLUSIONS: LPA may regulate a MYO5B-independent trafficking mechanism and brush border maturation, and therefore be developed for treatment of MVID.

Levothyroxine dose adjustment in hypothyroid patients following gastric sleeve surgery.

INTRODUCTION: Euthyroid patients show decreased TSH level following sleeve gastrectomy. However, studies of levothyroxine absorption after bariatric surgery reported contradictory results and data on levothyroxine dose adjustment according to weight are sparse. The aim of this study was to evaluate levothyroxine dose adjustment during weight loss following sleeve surgery. METHOD: This retrospective study assessed change in levothyroxine dose in patients undergoing sleeve gastrectomy at the university hospital center of Nîmes (France) between January 2010 and March 2016. Patients were receiving standard bariatric surgery follow-up with levothyroxine therapy for hypothyroidism. RESULTS: Fifty-two of the 271 patients who underwent sleeve gastrectomy (19.2%) were being treated with levothyroxine. Among these patients, 31 were followed up for 12 months, including 12 who were followed up for 24 months. Mean weight loss was 35±11kg at 12 months and 41.8±10.2 kg at 24 months. Daily levothyroxine dose decreased from 108 [88-144] µg/day to 94 [63-125] µg/day at 12 months and 69 [44-134] µg/day at 24 months, with positive correlation between dose and weight loss at 12 months (P=0.03). Weight-adjusted dose was 1.04 [0.81-1.24] µg/kg/day at baseline, 1.14 [0.85-1.66] µg/kg/day at 12 months, and 0.85 [0.53-2.10] µg/kg/day at 24 months, showing no correlation with weight loss. Median TSH level dropped to 1.30 [0.63-2.27] mIU/l at 12 months and 1.48 [1.08-2.42] mIU/l at 24 months. CONCLUSION: Despite a decrease in daily levothyroxine dose correlating with weight loss at 12 months, the absence of correlation with weight-adjusted dose suggests the involvement of confounding factors such as poor levothyroxine absorption or altered thyroid function. Further studies are required to elucidate the absorption of levothyroxine.

Successful Treatment of Hereditary Folate Malabsorption With Intramuscular Folinic Acid.

BACKGROUND: Hereditary folate malabsorption is a multisystem disease owing to biallelic variants in the gene encoding the proton-coupled folate transporter. Hereditary folate malabsorption is treated with folinic acid, aimed to restore blood and cerebrospinal fluid folate levels. Little is known as to whether oral or intramuscular supplementation of folinic acid is most effective. METHODS: Here we describe a one-year-old boy with hereditary folate malabsorption presenting with the typical features including failure to thrive, aphthous stomatitis, macrocytic anemia along with severe developmental impairment and epilepsy, as well as a magnetic resonance imaging of the brain showing bilateral occipital, cortical calcifications characteristic of hereditary folate malabsorption. We compared the effect of treatment with oral folinic acid versus intramuscular folinic acid supplementation by measuring plasma and cerebrospinal fluid folate levels. RESULTS: Compared with oral administration, intramuscular treatment resulted in higher folate levels in blood and, most importantly, normalization of folate levels in cerebrospinal fluid. Clinically, nearly all systemic and neurological symptoms resolved. CONCLUSION: Normal cerebrospinal fluid folate levels can be achieved in individuals with hereditary folate malabsorption with intramuscular (but not with oral) administration of folinic acid.

Levothyroxine Therapy in Gastric Malabsorptive Disorders.

Oral levothyroxine sodium is absorbed in the small intestine, mainly in the jejunum and the ileum being lower the absorption rate at duodenal level. The time interval between the ingestion of oral thyroxine and its appearance in the plasma renders unlike a gastric absorption of the hormone. However, several evidence confirm the key role of the stomach as a prerequisite for an efficient absorption of oral levothyroxine. In the stomach, in fact, occur key steps leading to the dissolution of thyroxine from the solid form, the process bringing the active ingredient from the pharmaceutical preparation to the aqueous solution. In particular, gastric juice pH, volume, viscosity, as well as gastric emptying time seem to be the most important limiting factors. These hypotheses are confirmed by the detection of an increased need for levothyroxine in patients with Helicobacter pylori infection, chronic atrophic gastritis, gastroparesis, or in simultaneous treatment with drugs interfering with gastric acidic output. The aim of the present article is to focus on the knowledge of pathophysiologic events that determine the absorptive fate of traditional (tablet) and alternative thyroxine preparations (softgel capsule and liquid solution) in patients bearing gastric disorders.

Treatment of microscopic colitis: the role of budesonide and new alternatives for refractory patients.

Microscopic colitis is a common cause of chronic watery diarrhea with a great impact on patient quality of life. Microscopic colitis includes two histological subtypes: collagenous colitis and lymphocytic colitis. Due to the increasing incidence and awareness of this disease over the last decades, several international guidelines have been recently published. However, there is still significant heterogeneity in the management of these patients, and treatments without solid scientific evidence support are often used in clinical practice. This article reviews the therapeutic role of budesonide in microscopic colitis and summarizes the current evidence regarding other treatments available for this disease, especially for the management of refractory patients. Finally, an updated treatment algorithm is proposed.

Do Specialized Bariatric Multivitamins Lower Deficiencies After Sleeve Gastrectomy?

BACKGROUND: Vitamin and mineral deficiencies are common after a sleeve gastrectomy (SG). The aim of this study is to examine the effectiveness of a specialized bariatric multivitamin (WLS Optimum) for SG patients on deficiencies compared with a regular multivitamin (MVS) for up to 5 years. METHODS: Data of all patients who underwent a SG procedure in the Catharina Hospital Eindhoven (CZE) between July 2011 and July 2016 were collected and retrospectively analyzed. All patients who completed a preoperative blood test and at least one blood withdrawal during the first operative year were included in this study. RESULTS: This study included 970 patients; 291 patients in the WLS-user group and 679 patients in the non-WLS-user group. In favor of the user group, significantly less de novo deficiencies were found of vitamin B1 (2 years) and vitamin B6 (two and three), folic acid (1 and 2 years), and vitamin B12 (at 1 year). Binomial logistic regression showed a significant influence of multivitamin supplementation mainly on ferritin; vitamins B1, B6, B12, and D; and folic acid, (all p < 0.05). The total number of de novo deficiencies was significantly reduced during the whole study for all WLS Optimum users. CONCLUSIONS: Vitamin deficiencies are common, and postoperative nutritional management after SG is underestimated. The use of a specialized multivitamin supplement resulted in higher mean serum concentrations and less deficiencies of vitamin B1, folic acid, and vitamin B12. This study shows that SG patients benefit from the specialized multivitamin supplements, but adjustments are required for iron and vitamin B6 content.

Nutrition management of congenital glucose-galactose malabsorption: Case report of a Chinese infant.

RATIONALE: Congenital glucose-galactose malabsorption (CGGM) is a rare, autosomal recessive, hereditary disease that usuallypresents in newborns. CGGM manifests as severe diarrhea, hyperosmolar dehydration, and malnutrition. It does not respond to routine treatment and often is life-threatening. PATIENT CONCERNS: We described a Chinese infant girl with refractory diarrhea, who suffered from severe dehydration and malnutrition even if with fluid replacement therapy and fed with several special formulas. DIAGNOSES: The genetic analysis identified CGGM with SLC5A1 mutations. c.1436G > C (p.R479T) was a novel mutation. INTERVENTIONS: The patient was managed by free-glucose and galactose formula, and then special low-carbohydrate dietary therapy. OUTCOMES: The patient improved immediately after starting a free-glucose and galactose formula, and kept healthy with special low-carbohydrate diet. She had been followed up with nutritional management for 20 months. LESSONS: This report highlights the importance of differential diagnosis of congenital diarrhea and enteropathies. For CGGM, free-glucose and galactose milk powder was the most effective treatment. Low-carbohydrate diet gradually introduced was still a great challenge that requires continuing guidance from child nutritionists and dietitians. Long-term nutrition management was extremely important to ensure the normal growth and development of children.

[IMERSLUND-GRÄSBECK SYNDROME CONGENITAL FORM OF VITAMIN B12 DEFICIENCY ANEMIA].

Normal red blood cells maturation depends on many different hematological factors, including vitamin (vit.) B12. Megaloblastic anemias are basically caused by vit. B12 deficiency. In childhood the deficiency of this vitamin is extremely rare. The article captures findings of observation of the patient with rare form congenital vit. B12 deficiency anemia - Imerslund-Gräsbeck syndrome. The disease is characterized with selective intestinal malabsorption of vit. B12 and permanent proteinuria, without sings of kidney disease. The diagnosis was confirmed by our team in early childhood and based on the history, clinical and paraclinical data. After two weeks of specific treatment with vit. B12 , complete clinical - hematological remission was achieved. Treatment includes lifelong vit. B12 injections once per month. Cathamnesic observation for 18 months revealed that the patient is in remission, but there was continued macrocytosis of red blood cells and mild proteinuria. The presented case is interesting as a rare case of megaloblastic anemia caused by vit. B12 deficiency in childhood. Such patients often treated under different diagnosis. In such cases early diagnosis, treatment and prevention are crucial for the good prognosis.

Off-Label Teduglutide Therapy in Non-intestinal Failure Patients with Chronic Malabsorption.

BACKGROUND: Teduglutide, a glucagon-like peptide 2 analog, has demonstrated efficacy in treating adult patients with short bowel syndrome (SBS) and dependence on parenteral nutrition (PN), but its role in chronic malabsorptive states that do not necessitate PN remains uncertain. AIMS: To evaluate teduglutide use beyond its approved indications and to discuss the results of this adjunctive treatment in patients resistant to established therapy. RESULTS: This series reports four patients treated with teduglutide off-label. The first case had Crohn's disease (CD) with persistent colocutaneous fistulae that demonstrated complete closure after 8 months of teduglutide therapy. The second case involved a PN-dependent CD patient with persistent fistulae and intra-abdominal abscesses who weaned off PN and had a significant improvement in her nutritional status after 3 months of teduglutide therapy. The third case had CD complicated by severe malnutrition and previous PN-associated line infections, but by 9 months of teduglutide therapy, she gained 5 kg and no longer required re-initiation of PN. The fourth case had a high-output diverting ileostomy with resultant impaired healing of a stage IV decubitus ulcer, and after 2 months of therapy, the patient's pre-albumin increased by 250% and the ulcer had decreased by 40% in size. CONCLUSION: The use of teduglutide might be broadened to include patients with functional SBS not meeting strict criteria for intestinal failure. Further studies should evaluate the efficacy of teduglutide in patients who may require short-term small intestine rehabilitation or who have chronically impaired absorptive capacity not yet requiring PN.

Imerslund-Gräsbeck Syndrome in an Infant with a Novel Intronic Variant in the AMN Gene: A Case Report.

Imerslund-Gräsbeck syndrome (IGS) is a rare autosomal recessive disorder clinically characterized by megaloblastic anemia, benign mild proteinuria, and other nonspecific symptoms. Several pathogenetic variants in the amnionless (AMN) or cubilin (CUBN) genes have been described in IGS. We describe a case of IGS with urinary tract infection and mild but persistent proteinuria at onset in an 11-month-old female child. With the appearance of macrocytic anemia, aphthous stomatitis, and neurological signs, IGS was clinically suspected, and vitamin B12 parenteral therapy was started. Sequence analysis showed the presence of a novel intronic variant c.513+5G>A of AMN, never before described in the literature, that was in compound heterozygosity with the known pathogenetic variant c.1006+34_1007-31del. Analysis extension to the parents revealed the presence of variant c.1006+34_1007-31 in the father and c.513+5G>A in the mother. In the present case with IGS, the novel intronic variant of AMN was identified in "trans" with a known pathogenic variant (c.1006-31 del) and the new variant was interpreted to be pathogenetic since it was not found in the public database of polymorphisms and because it was predicted to alter a donor splicing site. Our case underlines the relevance in detecting certain subtle symptoms, such as mild but persistent proteinuria associated with megaloblastic anemia, to reach a correct diagnosis of a rare but treatable disorder.

Daily oral cyanocobalamin supplementation in Beagles with hereditary cobalamin malabsorption (Imerslund-Gräsbeck syndrome) maintains normal clinical and cellular cobalamin status.

BACKGROUND: Efficacy of PO cobalamin (Cbl) supplementation in dogs with hereditary Cbl malabsorption (Imerslund-Gräsbeck syndrome, IGS) is unknown. OBJECTIVES: To evaluate PO Cbl supplementation in Beagles with IGS previously treated parenterally. We hypothesized that 1 mg cyano-Cbl daily PO would maintain clinical and metabolic remission. ANIMALS: Three client-owned Beagles with IGS and 48 healthy control dogs. METHODS: Prospective study. Daily PO cyanocobalamin (cyano-Cbl; 1 mg) supplementation was monitored for 13 (2 dogs) and 8 months (1 dog). Health status was assessed by owner observations. Methylmalonic acid (MMA)-to-creatinine concentrations were measured using an ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-TMS) method on urine samples collected monthly. Concurrent measurements of serum MMA concentration (n = 7; UPLC-TMS) were available for 1 dog. RESULTS: All dogs remained in excellent health during PO supplementation. Urine MMA remained consistently low in 2 dogs (median, 2.5 mmol/mol creatinine; range, 1.2-9; healthy dogs [n = 30], median, 2.9 mmol/mol creatinine; range, 1.3-76.5). Urine MMA ranged from 38.9-84.9 mmol/mol creatinine during the first 6 months in 1 dog already known to excrete comparable amounts when supplemented parenterally. Brief antibiotic treatment for an unrelated condition after 6 months resulted in low urine MMA (median, 2.8 mmol/mol creatinine; range, 1.9-4.8) for the next 7 months. All concurrent serum MMA concentrations (median, 651 nmol/L; range, 399-919) before and after month 6 were within the established reference interval (393-1476 nmol/L; n = 48). CONCLUSIONS AND CLINICAL IMPORTANCE: One milligram of cyano-Cbl daily PO appears efficacious for maintaining normal clinical status and normal cellular markers of Cbl metabolism in Beagles with IGS.