ESPE Abstracts

Introduction: Human growth is a multifactorial process involving genetic, hormonal, nutritional and environmental factors. Genome-wide association studies (GWAS) have shown that >400 genes are associated with adult height. African Baka Pygmies represent an isolated and well-confined small population with short stature of unknown etiology. In previous studies we reported an 8-fold reduced GH receptor gene expression and reduced serum levels of IGF-I and GHBP compared with sympatric adult Bantu individuals, while GH concentrations were normal. However, no association was found with sequence variants of the GHR gene. So far, in none of the pygmy populations the genetic cause of short stature has been discovered.

Materials and Methods: In an effort to discover the genetic cause of the pygmy phenotype, we enrolled 84 Baka Pygmies and 20 sympatric normally-statured Bantu neighbors living in Southeast Cameroon. Mean height SDS was -3.96 in male pygmies compared to -1.24 SDS in sympatric Bantu males, and -2.09 in female pygmies and -1.02 in Bantu females (P < 0.05). All subjects signed informed consent to participate in this study which was approved by the Research Ethic Committee of the University of Pavia. On DNAs from phenotypically selected 8 representative Baka Pygmies and 5 Bantu individuals, whole exome sequencing (WES) was performed to detect variants in genes and their regulatory regions associated with the pygmies’ reduced stature. Bioinformatic analysis and functional classification of the variants were carried out and results were validated in 76 Baka and 15 Bantu individuals.

Results: WES data analysis revealed 29 single nucleotide polymorphisms (SNPs) significantly associated with reduced height in the Baka population. Remarkably, Baka Pygmies exhibited a significant increase in novel identified SNPs compared to Bantu subjects (i.e. 515.25±63.7 vs 330.4±39.5, P=0.014 ANOVA One-Way). Around 1% of the identified variants in Baka Pygmies were predicted as high-impact (i.e. producing truncation, or loss of protein function). The selected variants were then validated in the larger cohort. A promising variant was rs7629425, a C/T SNP located in the 5’-UTR of the HYAL2 gene, 9 nucleotides upstream of the exon 2 coding sequence. The frequency of the alternative allele was significantly increased compared to African and non-African populations (P=0.032, Chi-Square). An in vitro luciferase assay in HeLa cells showed significant differences in transcription modulation of the reporter gene for the rs7629425, C/T alleles (P=0.024).

Conclusion: Our results suggest that the HYAL2 gene variant may play a role in the etiology of short stature in Baka pygmies.