Severe congenital microcephaly with AP4M1 mutation, a case report

Area of Science:

• Genetics
• Neuroscience
• Developmental Biology

Background:

• Autosomal recessive defects in Adaptor Protein complex-4 (AP4) subunits (B1, E1, M1, S1) are associated with developmental delay, intellectual disability, spasticity, and postnatal microcephaly.
• AP4 complexes are crucial for intracellular trafficking and protein sorting, impacting various cellular processes.

Observation:

• A patient presented with severe microcephaly of prenatal onset, progressive spasticity, developmental delay, and severe intellectual deficiency.
• Exome sequencing revealed a homozygous mutation in AP4M1 (p.Arg338X), leading to a truncated protein with predicted loss of function.
• Heterozygous variants in ATR, MCPH1, and BLM, known causes of primary microcephaly, were also identified.

Findings:

• The identified AP4M1 mutation expands the clinical phenotype to include severe prenatal-onset microcephaly.
• The premature stop codon in AP4M1 affects the Mu homology domain, suggesting a critical role in protein function.
• The genetic findings suggest potential shared mechanisms between AP4 defects and other genetic causes of congenital microcephaly.

Implications:

• This study broadens the understanding of AP4M1-related disorders and their phenotypic spectrum.
• The findings suggest that AP4 complex dysfunction may contribute to prenatal neuronal depletion, a mechanism also observed in other congenital microcephaly syndromes.
• Further research into AP4 complex function could reveal novel therapeutic targets for neurodevelopmental disorders.