FRMPD4 mutations cause X-linked intellectual disability and disrupt dendritic spine morphogenesis

Area of Science:

• Neuroscience
• Genetics
• Developmental Biology

Background:

• FRMPD4 (FERM and PDZ Domain Containing 4) is a neural scaffolding protein crucial for dendritic spine morphogenesis and mGluR signaling.
• Dendritic spines are vital for synaptic plasticity and cognitive function.

Purpose of the Study:

• To genetically and functionally characterize novel FRMPD4 mutations associated with X-linked intellectual disability (ID).
• To elucidate the role of FRMPD4 in cognitive development and neuronal function.

Main Methods:

• Genetic analysis of affected individuals from four families.
• Functional studies including protein interaction assays and neuronal transfection.
• Behavioral studies using frmpd4-knockout mice (Morris Water Maze test).

Main Results:

• Identified four deleterious FRMPD4 mutations (deletion, nonsense, frameshift, missense) in ten male patients with moderate to severe ID, language delay, seizures, and behavioral disturbances.
• A frameshift mutation disrupted FRMPD4 binding with PSD-95 and HOMER1, impairing spine density in hippocampal neurons.
• frmpd4-KO mice exhibited spatial learning and memory deficits.

Conclusions:

• FRMPD4 mutations cause a new X-linked ID syndrome.
• FRMPD4 is essential for normal cognitive development and function in humans and mice.
• Mutations likely lead to ID by disrupting glutamatergic neuron dendritic spine morphogenesis.