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A research team led by Dr. Sheng Nengyin of the Kunming Institute of Zoology (KIZ) of the Chinese Academy of Sciences has reframed ZC4H2-associated rare disorder (ZARD)—a disorder marked by intellectual disability, developmental delays, muscle weakness and other neurological or physical abnormalities—as a "disease spectrum" rather than a condition driven by a single mechanism.

Previously, the team demonstrated that ZC4H2 acts as a postsynaptic regulator of excitatory synaptic activity and brain cognition by modulating the protein stability of AMPA receptor subunits GluA1 and GluA2. However, it was unclear whether the same pathological mechanisms were at work in patients carrying different ZC4H2 variants, despite their clinical similarities.

Now, in more recent research, the team has shown that different pathogenic mutations in the same gene can produce nearly identical cognitive deficits through diametrically opposite synaptic mechanisms. The findings suggest that intervention should be guided by the specific mutation rather than the diagnosis alone.

In this new study, the team first expressed wild-type ZC4H2 and 23 pathogenic mutants in N2A cells. They identified two distinct classes: one that lost the ability to regulate excitatory AMPA receptor subunits GluA1/GluA2 (loss-of-function) and another that retained AMPA regulation but abnormally suppressed inhibitory GABAₐ receptor subunits α1/β1 (gain-of-function).

Electrophysiological recordings on hippocampal slices confirmed that the two classes specifically disrupted excitatory and inhibitory transmission, respectively.

To link mechanism to behavior, the researchers generated two knock-in mouse models carrying representative patient mutations: ZC4H2ᴸ⁶⁶ᴴ/ʸ and ZC4H2R²¹³ᵂ/ʸ.

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