The genetic basis of Pierre Robin Sequence

Introduction: The HAND genes encode a group of evolutionarily conserved basic helix-loop-helix (bHLH) transcription factors that play important roles in the development of structures derived from neural crest cells. Recent studies in mice have shown that neural crest-specific deletion of Hand1 and either a heterozygous deletion of Hand2 or deletion of the ventrolateral branchial arch expression of Hand2 results in a phenotype that resembles human Pierre Robin Sequence (PRS). PRS in humans is characterized by a triad of craniofacial defects, which include mandibular micrognathia, cleft of the secondary palate and glossoptosis.

Objective: To determine the role of HAND1, HAND2, and the branchial arch enhancer regulatory element of HAND2 in the pathogenesis of PRS.

Methods: Eight patients with PRS were recruited for the study and buccal swabs obtained and processed using standard techniques. Whole genome amplification was performed to obtain sufficient DNA for analysis. The samples were amplified by PCR and sequenced using primer sets for the coding regions of the HAND genes, as well as the enhancer of HAND2.

Results: Mutational analysis revealed a guanine to cytosine missense mutation in the first exon of HAND2 in one patient. Sequence alignment of multiple HAND2 sequences revealed the mutation changes of a highly conserved arginine residue to proline. Sequencing of 100 control chromosomes did not show a change in nucleotide at this position.

Conclusion: This putative disease-associated sequence variation in HAND2 in a patient with PRS is suggestive of an essential role for the HAND genes during normal craniofacial development. We are currently designing in vitro functional assays to determine the functional effects of the mutation on the resulting protein. Furthermore, additional analysis of those individuals in whom mutations were not found is warranted to better define other genetic determinants for this clinically challenging craniofacial disorder.

Supported by NIH-U24 (DE16472), BOHF.