SLC39A14 causing hypermanganesemia associated with infantile onset dystonia

Inspired by a colleague's patient

Marti-Sanchez L, Ortigoza-Escobar JD, Darling A, Villaronga M, Baide H, Molero-Luis M, Batllori M, Vanegas MI, Muchart J, Aquino L, Artuch R, Macaya A, Kurian MA, Dueñas P. Hypermanganesemia due to mutations in SLC39A14: further insights into Mn deposition in the central nervous system. Orphanet J Rare Dis. 2018 Jan 30;13(1):28.

Abstract

BACKGROUND:

The SLC39A14, SLC30A10 and SLC39A8 are considered to be key genes involved in manganese (Mn) homeostasis in humans. Mn levels in plasma and urine are useful tools for early recognition of these disorders. We aimed to explore further biomarkers of Mn deposition in the central nervous system in two siblings presenting with acute dystonia and hypermanganesemia due to mutations in SLC39A14. These biomarkers may help clinicians to establish faster and accurate diagnosis and to monitor disease progression after chelation therapy is administered.

RESULTS:

A customized gene panel for movement disorders revealed a novel missense variant (c.311G > T; p.Ser104Ile) in SLC39A14 gene in two siblings presenting at the age of 10 months with acute dystonia and motor regression. Mn concentrations were analyzed using inductively coupled mass spectrometry in plasma and cerebrospinal fluid, disclosing elevated Mn levels in the index case compared to control patients. Surprisingly, Mn values were 3-fold higher in CSF than in plasma. We quantified the pallidal index, defined as the ratio between the signal intensity in the globus pallidus and the subcortical frontal white matter in axial T1-weighted MRI, and found significantly higher values in the SLC39A14 patient than in controls. These values increased over a period of 10 years, suggesting the relentless pallidal accumulation of Mn. Following genetic confirmation, a trial with the Mn chelator Na2CaEDTA led to a reduction in plasma Mn, zinc and selenium levels. However, parents reported worsening of cervical dystonia, irritability and sleep difficulties and chelation therapy was discontinued.

CONCLUSIONS:

Our study expands the very few descriptions of patients with SLC39A14 mutations. We report for the first time the elevation of Mn in CSF of SLC39A14 mutated patients, supporting the hypothesis that brain is an important organ of Mn deposition in SLC39A14-related disease. The pallidal index is an indirect and non-invasive method that can be used to rate disease progression on follow-up MRIs. Finally, we propose that patients with inherited defects of manganese transport should be initially treated with low doses of Na2CaEDTA followed by gradual dose escalation, together with a close monitoring of blood trace elements in order to avoid side effects.

Juneja M, Shamim U, Joshi A, Mathur A, Uppili B, Sairam S, Ambawat S, Dixit R, Faruq M. A novel mutation in SLC39A14 causing hypermanganesemia associated with infantile onset dystonia. J Gene Med. 2018 Mar 2:e3012.

Abstract

BACKGROUND:

Mutations in SLC39A14 cause a recessive disorder of manganese (Mn) metabolism that manifests as childhood onset progressive neurodegeneration characterized by parkinsonism and dystonia.

METHODS:

The present study genetically investigated a case of hypermanganesemia. We describe a family where an affected child with a history of progressive neurodegeneration showed symptoms of dystonia with increased levels of blood Mn and altered signal intensities in globus pallidus and dentate nucleus. Whole exome sequencing was conducted to genetically investigate the pathology in the child, which allowed us to identify a novel homozygous causal mutation in SLC39A14.

RESULTS:

Insilico modeling of the novel homozygous causal mutation in SLC39A14 predicted that it was deleterious, affecting Mn binding and transportation of metal by transmembrane instability of the protein structure. The clinical features of other reported mutations in SLC39A14 were also reviewed and the clinical spectrum in our case conforms to the described neurological abnormalities.

CONCLUSIONS:

We conclude that the mutation identified in SLC39A14 in our case is a novel variation linked to recessive disorders of hypermaganesemia and dystonia.