PKAN neurodegeneration and residual PANK2 activities in patient erythrocytes

Abstract

Objective Pantothenate kinase 2‐associated neurodegeneration (PKAN) is a rare neurodegenerative disease caused by mutations in the pantothenate kinase 2 (PANK2) gene. PKAN is associated with iron deposition in the basal ganglia and, occasionally, with the occurrence of misshaped erythrocytes (acanthocytes). The aim of this study was to assess residual activity of PANK2 in erythrocytes of PKAN patients and to correlate these data with the type of PANK2 mutations and the progression of neurodegeneration. Methods Residual PANK2 activities in erythrocytes of 14 PKAN patients and 14 related carriers were assessed by a radiometric assay. Clinical data on neurodegeneration included the Barry–Albright Dystonia Scale (BAD‐Scale) besides further general patient features. A molecular visualization and analysis program was used to rationalize the influence of the PKAN causing mutations on a molecular level. Results Erythrocytes of PKAN patients had markedly reduced or no PANK2 activity. However, patients with at least one allele of the c.1583C > T (T528M) or the c.833G > T (R278L) variant exhibited 12–56% of residual PANK2 activity. In line, molecular modeling indicated only minor effects on enzyme structure for these point mutations. On average, these patients with c.1583C > T or c.833G > T variant had lower BAD scores corresponding to lower symptom severity than patients with other PANK2 point mutations. Interpretation Residual erythrocyte PANK2 activity could be a predictor for the progression of neurodegeneration in PKAN patients. Erythrocytes are an interesting patient‐derived cell system with still underestimated diagnostic potential.

A Potential Citrate Shunt in Erythrocytes of PKAN Patients Caused by Mutations in Pantothenate Kinase 2

“…PANK2 activity was determined as previously described [ 7 ]. Briefly, washed erythrocytes were hypotonically lysed, centrifuged (16,000× g , 20 min, 4 °C), and total protein in the supernatant was determined at 280 nm (NanoDrop 2000C, ThermoFisherScientific, Waltham, MA, USA).…”

“…To detect PANK2 in mature erythrocytes, however, was surprising as it is known to be primarily localized in mitochondria [ 5 , 6 ], which are absent in this cell type. However, our recent study on PKAN erythrocytes revealed that PANK2 actually is the only isoform present and active in erythrocytes [ 7 ]. We found that patients who were homozygous or compound heterozygous for the c.1583C > T (T528M) mutation had a significant residual PANK2 activity in their erythrocytes, which correlated with a tendency to slower disease progression.…”

Outcome Measures in OBPP

“…The Box and Blocks timed test measures unilateral dexterity by having children move blocks from one side a box to another using the dominant hand and the non-dominant hand [65]. The Barry-Albright Dystonia (BAD) scale rates the severity of dystonia in eight different body regions-eyes, mouth, neck, trunk, both arms, and both legs [66].…”

Coenzyme a Biochemistry: From Neurodevelopment to Neurodegeneration

“…Even though the available clinical experience appears to be negative, this approach deserves further investigation to establish its molecular basis and the connection with functional effects of the different missense mutations in PANK2 protein. The analysis of the residual PANK2 activity in patients' erythrocytes could prove to be useful to this aim [101]. Pantethine, the disulphide form of Pant, was one of the first molecules to be tested for its capacity to rescue PANK2-related phenotypes.…”