Acute ischemic stroke in a young woman with the thiamine-responsive megaloblastic anemia syndrome

An extremely rare case of Rogers syndrome or thiamine responsive megaloblastic anemia

ABSTRACT

Rogers syndrome is an extremely rare autosomal recessive syndrome of which only 100 cases are known worldwide. It is characterized by thiamine-responsive megaloblastic anaemia, diabetes mellitus and sensorineural deafness. It results from the deficiency of a thiamine transporter protein. We herein report a 16-year-old Indian male referred to our centre with complaints of refractory anaemia, deafness, diabetes pulmonary arterial hypertension and tricuspid regurgitation. Based on the clinical features and haematologic picture and dramatic response of anaemia to thiamine therapy the possibility of a TRMA was considered. Sequencing analysis for TRMA revealed a homozygous c.242dup (p.Tyr81Ter) mutation of the SLC19A2 gene.

Genetic defects of thiamine transport and metabolism: A review of clinical phenotypes, genetics, and functional studies

Thiamine is a crucial cofactor involved in the maintenance of carbohydrate metabolism and participates in multiple cellular metabolic processes within the cytosol, mitochondria, and peroxisomes. Currently, four genetic defects have been described causing impairment of thiamine transport and metabolism: SLC19A2 dysfunction leads to diabetes mellitus, megaloblastic anemia and sensory-neural hearing loss, whereas SLC19A3, SLC25A19, and TPK1-related disorders result in recurrent encephalopathy, basal ganglia necrosis, generalized dystonia, severe disability, and early death. In order to achieve early diagnosis and treatment, biomarkers play an important role. SLC19A3 patients present a profound decrease of free-thiamine in cerebrospinal fluid (CSF) and fibroblasts. TPK1 patients show decreased concentrations of thiamine pyrophosphate in blood and muscle. Thiamine supplementation has been shown to improve diabetes and anemia control in Rogers' syndrome patients due to SLC19A2 deficiency. In a significant number of patients with SLC19A3, thiamine improves clinical outcome and survival, and prevents further metabolic crisis. In SLC25A19 and TPK1 defects, thiamine has also led to clinical stabilization in single cases. Moreover, thiamine supplementation leads to normal concentrations of free-thiamine in the CSF of SLC19A3 patients. Herein, we present a literature review of the current knowledge of the disease including related clinical phenotypes, treatment approaches, update of pathogenic variants, as well as in vitro and in vivo functional models that provide pathogenic evidence and propose mechanisms for thiamine deficiency in humans.

Loss-of-Function Mutation in Thiamine Transporter 1 in a Family With Autosomal Dominant Diabetes

Solute Carrier Family 19 Member 2 (SLC19A2) encodes thiamine transporter 1 (THTR1), which facilitates thiamine transport across the cell membrane. SLC19A2 homozygous mutations have been described as a cause of thiamine-responsive megaloblastic anemia (TRMA), an autosomal recessive syndrome characterized by megaloblastic anemia, diabetes, and sensorineural deafness. Here we describe a loss-of-function SLC19A2 mutation (c.A1063C: p.Lys355Gln) in a family with early-onset diabetes and mild TRMA traits transmitted in an autosomal dominant fashion. We show that SLC19A2-deficient β-cells are characterized by impaired thiamine uptake, which is not rescued by overexpression of the p.Lys355Gln mutant protein. We further demonstrate that SLC19A2 deficit causes impaired insulin secretion in conjunction with mitochondrial dysfunction, loss of protection against oxidative stress, and cell cycle arrest. These findings link SLC19A2 mutations to autosomal dominant diabetes and suggest a role of SLC19A2 in β-cell function and survival.

Recovered insulin production after thiamine administration in permanent neonatal diabetes mellitus with a novel solute carrier family 19 member 2 (SLC19A2) mutation

BACKGROUND

Solute carrier family 19 member 2 (SLC19A2) gene deficiency is one of the causes of permanent neonatal diabetes mellitus (PNDM) and can be effectively managed by thiamine supplementation. Herein we report on a male patient with a novel SLC19A2 mutation and summarize the clinical characteristics of patients with SLC19A2 deficiency.

METHODS

The genetic diagnosis of the patient with PNDM was made by sequencing and quantitative polymerase chain reaction. The clinical characteristics of PNDM were summarized on the basis of a systematic review of the literature.

RESULTS

The patient with PNDM had c.848G>A (p.W283X) homozygous mutation in SLC19A2. His father had a wild-type SLC19A2 (c.848G) and his mother was c.848G/A heterozygous. The patient and his father both had a diploid genotype (c.848A/A and c.848G/G). After oral thiamine administration, the patient's fasting C-peptide levels increased gradually, and there was a marked decrease in insulin requirements. A search of the literature revealed that thiamine treatment was effective and improved diabetes in 63% of patients with SLC19A2 deficiency.

CONCLUSIONS

A novel SLC19A2 mutation (c.848G>A; p.W283X) was identified, which was most likely inherited as segmental uniparental isodisomy. Insulin insufficiency in PNDM caused by SLC19A2 deficiency can be corrected by thiamine supplementation. The differential diagnosis of SLC19A2 deficiency should be considered in children with PNDM accompanied by anemia or hearing defects to allow for early treatment.

Beta cell function and clinical course in three siblings with thiamine-responsive megaloblastic anemia (TRMA) treated with thiamine supplementation

Three siblings with thiamine-responsive megaloblastic anemia (TRMA) with a homozygous c.454delGGCATinsAT mutation in SLC19A2 are described. The index case presented at 14 months' old with severe non-ketotic hyperglycemia, dehydration, seizures and sinovenous thrombosis. She was started on insulin and developed sensorineural hearing loss around 2 years old. Two siblings were found to have the same mutation and were started on thiamine. One sibling developed transient hyperglycemia after several years of thiamine supplementation of 12 mg/kg that resolved with an increased thiamine dose (23 mg/kg). A younger sibling continues to remain diabetes-free on thiamine (24 mg/kg). The clinical course in this family suggests that there is an effect of thiamine on pancreatic beta cell function in patients with TRMA given the resolution of impaired fasting glucose with increasing thiamine dose in one sibling and the lack of diabetes to date in the siblings that were treated early with thiamine.

Treatable Inborn Errors of Metabolism Due to Membrane Vitamin Transporters Deficiency

B vitamins act as cofactors for strategic metabolic processes. The SLC19 gene family of solute carriers has a significant structural similarity, transporting substrates with different structure and ionic charge. Three proteins of this family are expressed ubiquitously and mediate the transport of 2 important water-soluble vitamins, folate, and thiamine. SLC19A1 transports folate and SLC19A2 and SLC19A3 transport thiamine. PCFT and FOLR1 ensure intestinal absorption and transport of folate through the blood-brain barrier and SLC19A25 transports thiamine into the mitochondria. Several damaging genetic defects in vitamin B transport and metabolism have been reported. The most relevant feature of thiamine and folate transport defects is that both of them are treatable disorders. In this article, we discuss the biology and transport of thiamine and folate, as well as the clinical phenotype of the genetic defects.

Does early treatment prevent deafness in thiamine-responsive megaloblastic anaemia syndrome?

Thiamine-responsive megaloblastic anaemia (TRMA; OMIM 249270) syndrome is an autosomal recessive disorder characterized by diabetes mellitus, megaloblastic anaemia, and sensorineural deafness. Progressive hearing loss is one of the cardinal findings of the syndrome and is known to be irreversible. Whether the deafness in TRMA syndrome can be prevented is not yet known. Here, we report a four-month-old female infant diagnosed with TRMA syndrome at an early age. There was no hearing loss at the time of diagnosis. The patient's initial auditory evoked brainstem response measurements were normal. Although she was given thiamine supplementation regularly following the diagnosis, the patient developed moderate sensorineural hearing loss at 20 months of age, indicating that early diagnosis and treatment with oral thiamine (100 mg/day) could not prevent deafness in TRMA syndrome. It would be premature to draw general conclusions from one case, but we believe that further patient-based observations can shed light on the pathophysiology of this rare syndrome as well as prediction of its prognosis.

Thiamine-responsive megaloblastic anemia: identification of novel compound heterozygotes and mutation update

OBJECTIVE

To determine causative mutations and clinical status of 7 previously unreported kindreds with TRMA syndrome, (thiamine-responsive megaloblastic anemia, online Mendelian inheritance in man, no. 249270), a recessive disorder of thiamine transporter Slc19A2.

STUDY DESIGN

Genomic DNA was purified from blood, and SLC19A2 mutations were characterized by sequencing polymerase chain reaction-amplified coding regions and intron-exon boundaries of all probands. Compound heterozygotes were further analyzed by sequencing parents, or cloning patient genomic DNA, to ascertain that mutations were in trans.

RESULTS

We detected 9 novel SLC19A2 mutations. Of these, 5 were missense, 3 were nonsense, and 1 was insertion. Five patients from 4 kindreds were compound heterozygotes, a finding not reported previously for this disorder, which has mostly been found in consanguineous kindreds.

CONCLUSION

SLC19A2 mutation sites in TRMA are heterogeneous; with no regional "hot spots." TRMA can be caused by heterozygous compound mutations; in these cases, the disorder is found in outbred populations. To the extent that heterozygous patients were ascertained at older ages, a plausible explanation is that if one or more allele(s) is not null, partial function might be preserved. Phenotypic variability may lead to underdiagnosis or diagnostic delay, as the average time between the onset of symptoms and diagnosis was 8 years in this cohort.

Thiamine responsive megaloblastic anemia syndrome

Thiamine responsive megaloblastic anemia syndrome (TRMA) is a clinical triad characterized by thiamine-responsive anemia, diabetes mellitus and sensorineural deafness. We report a 4-year-old girl with TRMA whose anemia improved following administration of thiamine and this case report sensitizes the early diagnosis and treatment with thiamine in children presenting with anemia, diabetes and deafness.

Targeting and intracellular trafficking of clinically relevant hTHTR1 mutations in human cell lines

The micronutrient thiamine is required for normal growth and development of human tissues, and is accumulated into cells through the activity of plasma membrane thiamine transporters, e.g. hTHTR1 (human thiamine transporter 1). Recent genetic evidence has linked mutations in hTHTR1 with the manifestation of TRMA (thiamine-responsive megaloblastic anaemia), a condition also associated with diabetes mellitus, sensorineural deafness and retinal disorders. To examine how mutations in hTHTR1 impair thiamine accumulation, we have investigated the targeting and functional properties of several different hTHTR1 mutants in human cell lines derived from epithelia relevant to thiamine absorption or tissues implicated in TRMA pathology. These constructs encompassed two newly identified point mutations (P51L and T158R) and two truncations of hTHTR1 identical with those found in TRMA kindreds (W358X and Delta383fs). Our results reveal a spectrum of mutant phenotypes, underlining that TRMA can result from decreased thiamine transport activity underpinned by changes in hTHTR1 expression levels, cellular targeting and/or protein transport activity.

Novel mutation in theSLC19A2 gene in an African-American female with thiamine-responsive megaloblastic anemia syndrome

Thiamine-responsive megaloblastic anemia (TRMA) syndrome is an autosomal recessive disorder characterized by diabetes mellitus (DM), progressive sensorineural deafness, and thiamine-responsive anemia. Mutations in the SLC19A2 gene encoding a high-affinity thiamine transporter protein THTR-1 are responsible for the clinical features associated with TRMA syndrome. We report an African-American female with TRMA-syndrome associated with thyroid disease and retinitis pigmentosa caused by a novel mutation in the SLC19A2 gene. The patient presented at 12 months of age with paroxysmal atrial tachycardia and hepatosplenomegaly. One month later, she developed DM requiring intermittent insulin therapy. At 2-1/2 years of age, profound sensorineural hearing loss was discovered. By 4 years of age, daily insulin therapy (0.5 U/kg/day) was instituted and her insulin requirement gradually increased to 1.0 U/kg/day by 9 years of age. She developed optic atrophy, retinitis pigmentosa, and visual impairment by 12 years of age with severe restriction of peripheral vision by 16 years. At age 19, a thiamine-responsive normocytic anemia was discovered. She was diagnosed with autoimmune thyroiditis at 20 years and she experienced a psychotic episode associated with a mood disorder at age 21. With oral thiamine therapy, her insulin requirement decreased by 30% over a 20 month period. Molecular analysis revealed that the patient is homozygous for a missense mutation (C152T) in exon 1 of the SLC19A2 gene.

A novel mutation in the SLC19A2 gene in a Tunisian family with thiamine-responsive megaloblastic anaemia, diabetes and deafness syndrome

Thiamine-responsive megaloblastic anaemia (TRMA) syndrome with diabetes and deafness was found in two patients from a Tunisian kindred. The proband was homozygous for a novel mutation, 287delG, in the high-affinity thiamine transporter gene, SLC19A2. We demonstrated that fibroblasts from this patient exhibited defective thiamine transport. These data confirm that the SLC19A2 gene is the high-affinity thiamine carrier and that this novel mutation is responsible for TRMA syndrome.