Lenz-Majewski syndrome: How a single mutation leads to complex changes in lipid metabolism

Area of Science:

• Biochemistry
• Cell Biology
• Genetics

Background:

• Lenz-Majewski syndrome (LMS) is a rare genetic disorder with severe physical and mental abnormalities.
• Gain-of-function mutations in the PTDSS1 gene, encoding phosphatidylserine synthase 1 (PSS1), are identified as a cause of LMS.
• Mutant PSS1 enzymes are insensitive to product inhibition, leading to uncontrolled phosphatidylserine (PS) production.

Purpose of the Study:

• To investigate the molecular mechanisms underlying Lenz-Majewski syndrome.
• To elucidate how PTDSS1 mutations disrupt cellular lipid metabolism.
• To understand the link between PS synthesis and phosphatidylinositol 4-phosphate (PI4P) metabolism in LMS.

Main Methods:

• Whole exome sequencing in LMS patients.
• Biochemical analysis of PSS1 enzyme activity and PS production.
• Measurement of PI4P levels in various cellular compartments.

Main Results:

• Mutations in PTDSS1 cause PSS1 to produce excessive PS, accumulating in the ER.
• Elevated ER PS activates Sac1 phosphatase, reducing PI4P levels in the Golgi and plasma membrane.
• Disruption of PI4P gradients impairs non-vesicular lipid transport from the ER.

Conclusions:

• Uncontrolled PS synthesis in LMS triggers widespread lipid metabolism dysregulation via PI4P pathway.
• The study reveals a critical metabolic link between PS synthesis and PI4P homeostasis.
• This finding offers new insights into the molecular basis of Lenz-Majewski syndrome.