Regular ArticleA frame-shift deletion in the PURA gene associates with a new clinical finding: Hypoglycorrhachia. Is GLUT1 a new PURA target?
Introduction
Genetic alterations in PURA or Pur-alpha (purine-rich element binding protein A) have been documented in humans as the origin of neurologic syndromes [1] and the cause for the 5q31.3 Microdeletion Syndrome phenotype [2], [3]. PURA is expressed in brain, muscle, heart and blood and it is known to be essential for normal brain development [4], [5]. Up to now, this disease has been documented to be caused by de novo, dominant mutations [1], [2]. Patients with this disorder have been described with hypotonia, feeding difficulties, severe developmental delay, respiratory difficulties, pituitary dysfunction, and epileptic/non-epileptic encephalopathy associated with delayed myelination [1], [6], [7], [8], [9], [10]. As in most neurologic diseases, these symptoms overlap with genetic and acquired encephalopathies of diverse origins, making diagnosis often a challenge.
PURA is a single-exon gene, that encodes a highly conserved multifunctional protein, member of the PUR family (Pur-alpha, Pur-beta and Pur-gamma) [11]. It is a DNA and RNA binding protein that plays an important role in cell proliferation, transcriptional regulation and mRNA trafficking [12], [11]. As a member of the PUR family, it has three conserved sequence-specific repeats: PUR domains I, II and III that are responsible for the protein's main functions [11]. Each PUR amino acid repeat consists of a β-sheet domain and an α-helical domain arranged in a “whirly fold,” structure in which the convex β-sheets form a surface for interaction with nucleic acids and the remaining helix portions are involved in protein-protein interactions [12], [13]. PUR I and II motifs are proposed to form intramolecular peptide-peptide bonds between each other, while the PUR III domain is responsible for homo-heterodimerization with another PUR protein or interaction with other proteins [14], [13] (Fig. 1). It has been shown that specifically PURA can regulate gene expression by binding directly to DNA promoters, or to different mRNAs and non-coding RNAs. It can also form DNA-mRNA-protein complexes, all features that make it an important transcriptional and translational regulator [15], [16].
SLC2A1 gene (clinically better known as GLUT1) is a member of the GLUT family of facilitative glucose transporters, which includes 13 genes. SLC2A1 was the first cloned and sequenced gene of the group and it encodes for GLUT1 protein [17]. GLUT1 is ubiquitously expressed in most tissues, but selectively higher in erythrocytes, brain microvessels and astroglia. Glucose is the essential substrate for brain metabolism and its transport across the blood-brain barrier depends on GLUT1 [18]. It is also important for glucose uptake in red blood cells since these cells´ metabolism is strictly glycolytic [19], [20]. GLUT1 deficiency syndrome classically presents with infantile seizures (often resistant to antiepileptic drugs), developmental delay, acquired microcephaly, hypotonia, spasticity, dystonia and in some cases hemolytic anemia all associated to its key biomarker: hypoglycorrhachia [21].
We report here a patient with a one-base frame-shift deletion in the PURA gene that presented an unusual phenotype including persistent hypoglycorrhachia. We propose a possible link between hypoglycorrhachia and PURA dysfunction postulating PURA as a GLUT1 regulator. We therefore hypothesize that mutations in PURA can decrease GLUT1 expression and in consequence provoke a GLUT1 deficiency-like phenotype.
Section snippets
Patient consent
Written informed consent was obtained from the patient's parents who agreed to use the patient's samples for research and data for publication. The blood samples used for research purposes were obtained within diagnostic or clinical control procedures. Blood protein from 4 anonymous healthy controls were used to compare with the patient.
Genetic testings
DNA extraction: IHEM, UNCuyo, CONICET - Mendoza, Argentina.
Leukocyte DNA from the patient and both parents was extracted using CTAB/chloroform-isoamyl alcohol
Patient's clinical findings
Female, second child of a non-consanguineous couple. Born at term with normal weight from an uneventful pregnancy, discharged on her 2nd day of life without complications. She was admitted to hospital on day 7 due to failure to thrive, poor suction and dehydration. She was noted to be profoundly hypotonic and continued admitted for further studies. Parents mentioned abnormally frequent hiccupping during the first week of life. Seizures and apneas started on day 8, needing ventilator support for
Discussion
We have presented a patient with a monoallelic defect in the PURA gene that causes the expression of a truncated dysfunctional protein, explaining the phenotype. This patient's clinical setting with marked hypoglycorrhachia and hypertrophic myocardiopathy expands PURA deficiency's phenotype since this has not been previously reported in patients [1], [2], [6] nor in PURA deficient mice models [4], [5]. We did not deepen our research in the cardiomyopathy, but PURA as a transcription regulator
Conflict of interest
The authors declare that they have no conflict of interest nor competing financial interests.
Funding
This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
Acknowledgements
The authors thank in first place the patient and her parents for contributing to PURA research. They also acknowledge Dr. Luis S. Mayorga (IHEM, UNCuyo, CONICET - Mendoza, Argentina) for helping with the manuscript edition. They thank Dr. Patricia S. Romano, Dr. Claudio Fader and Dr. Estela Muñoz's laboratories (IHEM, UNCuyo, CONICET - Mendoza, Argentina) for contributing with Western Blot supplies and also the physicians Dr. Hernán D. Eiroa and Dr. M.Soledad Monges (Hospital J.P. Garrahan,
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