Figure 1. Muscle pathology and genetic analysis of the hypoPP patient. (A) Histological examination of a biceps brachii muscle biopsy performed at age 2 years and 3 months. (i) Haematoxylin and eosin staining showed variation in fibre diameter, increased internal nuclei (black arrows), a necrotic fibre (white arrow) and subtle endomysial fibrosis (also seen in iii) (ii) Myosin ATPase histochemistry at pH 9.4 indicated type I fibre predominance (pale stained fibres). (iii) Gomori trichrome staining. (B) Sequence chromatogram demonstrating the heterozygous mutation c.2336 G>A; p.S779N in the proband (above) and sequence alignment of human Na+/K+-ATPase alpha subunits. ATP1A2-S779 and analogous serine residues are underlined. (C) Structural context of S779. Left: An overview of the Na+/K+-ATPase structure with the alpha subunit in grey, the beta subunit in blue and the gamma subunit in red. The two potassium ions are yellow spheres, S779 is in orange stick, and the ion-coordinating transmembrane helices are light cyan (M4), wheat (M5) and light blue (M6). The boundaries of the membrane are indicated by horizontal lines. Right: Close-ups of the ion binding sites viewed from the extracellular side, top with two potassium ions (yellow), bottom with three sodium ions (violet). S779 is close to ion binding sites I and III. The figure was made using PDB structures 2ZXE (potassium bound) and 3WGU (sodium bound).
Image published in: Sampedro Castañeda M et al. (2018)
© The Author(s) (2018). This image is reproduced with permission of the journal and the copyright holder. This is an open-access article distributed under the terms of the Creative Commons Attribution license
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