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Figure 1

Figure 1. Ultrastructural findings at the neuromuscular junction (NMJ). Control (A) and the patient (B–F). (A) Normal NMJ from a control demonstrating normal nerve terminal size and highly complex postsynaptic membrane folding with well formed secondary synaptic clefts. The arrow heads point to Schwann cell processes, which cap the nerve terminal (N), without extending into the synaptic cleft. The arrows point to the primary synaptic cleft (top) and at a secondary synaptic cleft (bottom). The asterisk in A–C is placed over the Schwann cell. (B) Small nerve terminal partially encased by a Schwann cell process, which intrudes into the synaptic space. (C) Small nerve terminal retracted from the synaptic space and completely engulfed by the Schwann cell. Note also pronounced simplification of the postsynaptic membrane (arrow). (D) Bifurcated nerve terminal with one nerve ending completely engulfed (top arrowhead) and the other ending partially encased (bottom arrowhead) by the Schwann cell. Note also pronounced widening of the primary synaptic cleft and reduction of the density of synaptic vesicles in the nerve terminal. (E) Nerve terminal divided in three small endings, which are encased by the Schwann cell and retracted from the postsynaptic membrane. (F) Pronounced reduction of the area of apposition between the nerve terminal and the postsynaptic membrane, widening of primary synaptic cleft and invasion of the synaptic space by Schwann cell processes (horizontal arrowheads). The vertical arrowheads point to two active zones, which in contrast to the control, are not apposing postsynaptic secondary clefts. (G) and (H) Quantification of the area of apposition between the nerve and muscle. (G) Bar graph representing the average length of apposition between nerve and muscle in 11 controls and 11 patient endplates. (H) Percentages of direct nerve–muscle apposition relative to the total length of the synaptic cleft in 24 controls and 11 patient endplates (mean (SEM)). Calibration marks (A–F) represent 1 μm.. From: Mutations in LAMB2 causing a severe form of synaptic congenital myasthenic syndrome.

R A Maselli, et al. J Med Genet. 2009 March;46(3):203-208.

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