Holoprosencephaly: from Homer to Hedgehog

Area of Science:

• Developmental biology
• Human genetics
• Neuroscience

Background:

• Holoprosencephaly (HPE) is a congenital disorder affecting forebrain and facial development, characterized by significant etiological heterogeneity and phenotypic variability.
• The severity of brain malformations in HPE often correlates with the degree of craniofacial abnormalities.
• Individuals with milder forms of HPE (microforms) may have normal cognition and brain imaging but can still transmit the condition to offspring, with some carriers being phenotypically normal.

Purpose of the Study:

• To explore the genetic and molecular underpinnings of Holoprosencephaly (HPE).
• To identify candidate genes and pathways involved in HPE etiology.
• To understand the relationship between genetic factors, brain development, and phenotypic expression in HPE.

Main Methods:

• Review of genetic studies identifying chromosomal rearrangements in HPE patients.
• Analysis of the role of the Sonic Hedgehog (SHH) signaling pathway in HPE.
• Investigation of genes involved in cholesterol metabolism and forebrain development as potential contributors to HPE.

Main Results:

• Recurrent chromosomal rearrangements point to specific gene loci critical for brain development in HPE.
• Sonic Hedgehog (SHH) was identified as the first causative gene for human HPE, with its function dependent on cholesterol modification.
• Candidate genes implicated in HPE include SHH pathway components, cholesterol metabolism elements, and genes crucial for developing forebrain.

Conclusions:

• HPE is genetically complex, involving multiple genes and pathways.
• The SHH pathway and cholesterol metabolism are key areas of investigation for HPE.
• Further research into genes affecting forebrain development is crucial for understanding HPE etiology and variability.