RAC1 Missense Mutations in Developmental Disorders with Diverse Phenotypes

Area of Science:

• Genetics
• Neuroscience
• Developmental Biology

Background:

• RAC1, a Rho GTPase, regulates critical cellular functions and is vital for normal development.
• RAC1 mutations are rare but can lead to significant developmental abnormalities.
• Understanding the precise impact of RAC1 variants is crucial for diagnosing and treating related disorders.

Purpose of the Study:

• To investigate the phenotypic spectrum associated with de novo missense RAC1 mutations.
• To elucidate the functional consequences of specific RAC1 variants on neuronal development.
• To establish RAC1 as a key player in a subset of rare developmental disorders.

Main Methods:

• Clinical evaluation of seven individuals with distinct de novo RAC1 mutations.
• In silico modeling to predict variant effects.
• Functional assays including mouse fibroblasts spreading and zebrafish overexpression models.

Main Results:

• Identified seven distinct de novo missense RAC1 mutations associated with varying developmental phenotypes.
• Observed a wide range of head circumferences (microcephaly to macrocephaly) linked to specific RAC1 variants.
• Demonstrated that certain RAC1 variants act as dominant-negative or constitutively active alleles, impacting neuronal development in vivo.

Conclusions:

• RAC1 mutations are central to a newly emerging category of rare developmental disorders.
• The study highlights the critical role of RAC1 in human brain development.
• International collaboration is essential for dissecting ultra-rare disorders caused by private missense mutations.