GLRX5-associated [Fe-S] cluster biogenesis disorder: further characterisation of the neurological phenotype and long-term outcome

Bindu Parayil Sankaran,Kaustuv Bhattacharya,Peter Procopis,Michel Tchan,Sachin Gupta,Yusof Rahman,Beena Devanapalli

doi:10.1186/s13023-021-02073-z

Bindu Parayil Sankaran, Kaustuv Bhattacharya + Show 5 more

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https://doi.org/10.1186/s13023-021-02073-z

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Abstract

BackgroundIdentification and characterisation of monogenic causes of complex neurological phenotypes are important for genetic counselling and prognostication. Bi-allelic pathogenic variants in the gene encoding GLRX5, a protein involved in the early steps of Fe-S cluster biogenesis, are rare and cause two distinct phenotypes: isolated sideroblastic anemia and a neurological phenotype with variant non-ketotic hyperglycinemia. In this study, we analysed the evolution of clinical and MRI findings and long-term outcome of patients with GLRX5 mutations.MethodsFour patients from three Australian families of Lebanese descent were identified. All patients presented in childhood and were followed up into adult life through multiple clinical assessments. All were prescribed sodium benzoate.ResultsAll patients (all females, age range 18–56 years) showed a complex neurological phenotype characterised by varying combinations of spastic paraparesis, length-dependent motor/sensory-motor axonal polyneuropathy, and psychiatric disturbances with variable intellectual disability. All had non-ketotic hyperglycinemia and a homozygous pathogenic c.151_153delAAG (p.K51del) change in GLRX5. Motor disability gradually progressed reaching moderate disability during adolescence and moderately severe disability during adult life. The major MRI finding was the upper cervical spinal cord signal changes with contrast enhancement noted in all and additional leukoencephalopathy in one. On follow up MRI, the white matter lesions diminished on a subsequent scan and then remained static over time. The spinal cord showed gliotic changes. Two patients have previously demonstrated low pyruvate dehydrogenase complex deficiency but none had plasma lactate elevation, nor biochemical evidence of branch-chain keto-dehydrogenase deficiency. Glycine levels reduced in patients that tolerated sodium benzoate, possibly stabilising clinical manifestations.ConclusionsThis report demonstrates that the p.K51del GLRX5 variant causes a distinct and predictable neurological phenotype. The clinical assessments spanning from childhood to adult life enable physicians to infer the natural history of GLRX5 related neurological disorder. There may be widespread metabolic consequences, and optimal management is unknown.

Highlights

Glutaredoxin5 (GLRX5) is a 156 amino acid mitochondrial protein, involved in iron-sulfur [Fe-S] cluster biogenesis [1]
Mutations in GLXR5 have been associated with two distinct phenotypes so far, variant non ketotic hyperglycinemia and isolated sideroblastic anemia [7, 8]
Our group described the clinical presentation of one patient in 2007 and subsequently another patient presenting with spastic diplegia was identified [9]. These two patients and a third with a similar phenotype led to the identification GLRX5 variant non ketotic hyperglycinemia as described by Baker et al [8, 10]

Summary

Introduction

Glutaredoxin (GLRX5) is a 156 amino acid mitochondrial protein, involved in iron-sulfur [Fe-S] cluster biogenesis [1]. Mutations in GLXR5 have been associated with two distinct phenotypes so far, variant non ketotic hyperglycinemia and isolated sideroblastic anemia [7, 8]. Our group described the clinical presentation of one patient in 2007 and subsequently another patient presenting with spastic diplegia was identified [9] These two patients and a third with a similar phenotype led to the identification GLRX5 variant non ketotic hyperglycinemia as described by Baker et al [8, 10]. Bi-allelic pathogenic variants in the gene encoding GLRX5, a protein involved in the early steps of Fe-S cluster biogenesis, are rare and cause two distinct phenotypes: isolated sideroblastic anemia and a neurological phenotype with variant non-ketotic hyperglycinemia. We analysed the evolution of clinical and MRI findings and long-term outcome of patients with GLRX5 mutations

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