Case Report: A rare form of congenital erythrocytosis due to SLC30A10 biallelic variants-differential diagnosis and recommendation for biochemical and genetic screening

Congenital erythrocytosis recognizes heterogeneous genetic basis and despite the use of NGS technologies, more than 50% of cases are still classified as idiopathic. Herein, we describe the case of a 3-year-old boy with a rare metabolic disorder due to SLC30A10 bi-allelic mutations and characterized by hypermanganesemia, congenital erythrocytosis and neurodegeneration, also known as hypermanganesemia with dystonia 1 (HMNDYT1). The patient was treated with iron supplementation and chelation therapy with CaNa2EDTA, resulting in a significative reduction of blood manganese levels and erythrocytosis indexes. Although it couldn't be excluded that the patient's developmental impairment was part of the phenotypic spectrum of the disease, after three months from starting treatment no characteristic extrapyramidal sign was detectable. Our findings suggest the importance of assessing serum manganese levels in patients with unexplained polycythemia and increased liver enzymes. Moreover, we highlight the importance of extended genetic testing as a powerful diagnostic tool to uncover rare genetic forms of congenital erythrocytosis. In the described patient, identifying the molecular cause of erythrocytosis has proven essential for proper clinical management and access to therapeutic options.

A novel homozygous SLC39A14 variant in an infant with hypermanganesemia and a review of the literature

BACKGROUND

Manganese (Mn) is an essential trace metal necessary for good health; however, excessive amounts in the body are neurotoxic. To date, three genes (SLC30A10, SLC39A8, and SLC39A14) have been discovered to cause inborn errors in Mn metabolism in humans. As very rare diseases, the clinical features require further clarification.

METHODS

A male Chinese patient who mainly presented with hypermanganesemia and progressive parkinsonism-dystonia was recruited for this study. We collected and analyzed clinical information, performed whole-exome sequencing (WES), and reviewed the relevant literature.

RESULTS

The motor-developmental milestones of the patient were delayed at the age of 4 months, followed by rapidly progressive dystonia. The patient displayed elevated Mn concentrations in blood and urine, and brain magnetic resonance imaging (MRI) showed symmetrical hyperintensity on T1-weighted images and hypointensity on T2-weighted images in multiple regions. A novel homozygous variant of the SLC39A14 gene (c.1058T > G, p.L353R) was identified. The patient was treated with disodium calcium edetate chelation (Na₂CaEDTA). Three months later, mild improvement in clinical manifestation, blood Mn levels, and brain MRI was observed. To date, 15 patients from 10 families have been reported with homozygous mutations of SLC39A14, with a mean age of onset of 14.9 months. The common initial symptom is motor regression or developmental milestone delay, with a disease course for nearly all patients involving development of progressive generalized dystonia and loss of ambulation before treatment. Additionally, hypermanganesemia manifests as Mn values ranging from 4- to 25-fold higher than normal baseline levels, along with brain MRI results similar to those observed in the recruited patient. Nine SLC39A14 variants have been identified. Seven patients have been treated with Na₂CaEDTA, and only one patient achieved obvious clinical improvement.

CONCLUSION

We identified a novel SLC39A14 mutation related to autosomal recessive hypermanganesemia with dystonia-2, which is a very rare disease. Patients present motor regression or delay of developmental milestones and develop progressive generalized dystonia. Chelation therapy with Na₂CaEDTA appears to effectively chelate Mn and increase urinary Mn excretion in some cases; however, clinical response varies. The outcome of the disease was unsatisfactory. This study expands the genetic spectrum of this disease.

Unusual magnetic resonance imaging of the head in manganese and ephedrone intoxication - a case report

Manganese intoxication leads to the accumulation of manganese in the brain, mostly in the globus pallidus, which clinically manifests as a L-DOPA - resistant parkinsonian syndrome with specific symptoms, such as spastic-hypokinetic dysarthria and postural instability. A new kind of manganese poisoning associated with drug abuse has been reported in Eastern European countries.

A CASE REPORT

We present an adult patient with neurological abnormalities secondary to manganese intoxication related to the abuse of psychoactive substances. High serum levels of manganese, hyperintense lesions on T1-weighted magnetic resonance imaging (MRI), and parkinsonism in this case confirmed the diagnosis. MRI results showed accumulation of manganese in the basal ganglia which caused an increased signal in this area of the brain on T1 weighted sequence. This is the second case reported with diffuse high signal intensity of the entire white matter due to manganese and ephedron neurointoxication. To the best of our knowledge, this is the first time such extensive pathological changes to cerebellar white matter, located near the fourth ventricle, have been described.

CONCLUSIONS

We suggest that chronic exposure to manganese and ephedron damaged the white matter in the cerebral hemispheres and continued to affect the periventricular area of the fourth ventricle, causing continuous changes to the white matter.

Zinc transporter 10 (ZnT10)-dependent extrusion of cellular Mn2+ is driven by an active Ca2+-coupled exchange

Manganese (Mn²⁺) is extruded from the cell by the zinc transporter 10 (ZnT10). Loss of ZnT10 expression caused by autosomal mutations in the ZnT10 gene leads to hypermanganesemia in multiple organs. Here, combining fluorescent monitoring of cation influx in HEK293-T cells expressing human ZnT10 with molecular modeling of ZnT10 cation selectivity, we show that ZnT10 is exploiting the transmembrane Ca²⁺ inward gradient for active cellular exchange of Mn²⁺ In analyzing ZnT10 activity we used the ability of Fura-2 to spectrally distinguish between Mn²⁺ and Ca²⁺ fluxes. We found that (a) application of Mn²⁺-containing Ca²⁺-free solution to ZnT10-expressing cells triggers an influx of Mn²⁺, (b) reintroduction of Ca²⁺ leads to cellular Mn²⁺ extrusion against an inward Mn²⁺ gradient, and (c) the cellular transport of Mn²⁺ by ZnT10 is coupled to a reciprocal movement of Ca²⁺ Remarkably, replacing a single asparagine residue in ZnT10 (Asp-43) with threonine (ZnT10 N43T) converted the Mn²⁺/Ca²⁺ exchange to an uncoupled channel mode, permeable to both Ca²⁺ and Mn²⁺ The findings in our study identify the first ion transporter that uses the Ca²⁺ gradient for active counter-ion exchange. They highlight a remarkable versatility in metal selectivity and mode of transport controlled by the tetrahedral metal transport site of ZnT proteins.

Recommendations for Manganese Supplementation to Adult Patients Receiving Long-Term Home Parenteral Nutrition: An Analysis of the Supporting Evidence

INTRODUCTION

Manganese (Mn) toxicity is often observed in adult patients receiving long-term home parenteral nutrition (HPN), and differing recommendations on the safe level of Mn administration to these patients have been made in the literature over the past 10 years.

METHODS

This systematic review used the National Health and Medical Research Council (NHMRC) evidence hierarchy to assess the design and strength of individual studies (high I to low IV) and the overall grade of evidence (grade A high to grade D low).

RESULTS

Eight studies met the inclusion criteria. Levels of evidence ranged from high (NHMRC II) to mid-level (III-3). A widespread recommendation in the literature for patients receiving long-term HPN is 55 µg (1 µmol) Mn/d.

CONCLUSION

The recommendation of 55 µg (1 µmol) Mn/d is of moderate-strength evidence (NHMRC B grade). There is limited evidence to support not supplementing Mn to patients receiving long-term HPN. Further intervention studies providing high-level evidence (II and above) are required to determine the safety of not supplementing Mn to all patients receiving long-term HPN.

Nramp1 and Other Transporters Involved in Metal Withholding during Infection

During the course of infection, many natural defenses are set up along the boundaries of the host-pathogen interface. Key among these is the host response to withhold metals to restrict the growth of invading microbes. This simple act of nutritional warfare, starving the invader of an essential element, is an effective means of limiting infection. The physiology of metal withholding is often referred to as "nutritional immunity," and the mechanisms of metal transport that contribute to this host response are the focus of this review.