ESPE Abstracts

Background: The genetic etiology of non-syndromic HI remains unknown in over 20% of all cases, and over 50% of diazoxide-responsive cases. Non-coding variants in HK1 have been suggested to cause HI by linkage-analysis (Pinney et al., 2008). More recently, variants within a regulatory region of HK1 intron 2 were reported in 17 individuals with HI (Wakeling et al., 2022). These variants have been proposed to cause HI by disrupting normal postnatal silencing of HK1 expression in beta-cells.

Objectives: Identify cases of HI due to non-coding variants in HK1 in a large, single-center cohort of children with HI with genetics negative HI, describe clinical characteristics, and evaluate HK1 expression in identified cases.

Methods: A 350bp region in intron 2 of HK1 was sequenced in children with genetics negative HI evaluated at our center (January 1997-April 2023). In cases where HK1 variants were identified and pancreatic specimens were available, HK1 expression in resected pancreas tissue was evaluated by immunofluorescence (IF) and/or qPCR.

Results: Twenty-eight percent (n=309/1117) of children genotyped at our center had genetics negative HI (n=49/666, 7% diazoxide-unresponsive; n=260/451, 58% diazoxide-responsive). HK1 intron 2 sequencing has been performed in 76% of genetics-negative cases (n=234/309). This identified 10 unique non-coding variants in intron 2 of HK1 in 13 children (5.6%, n=13/234). The HK1 variant was de novo in 9 cases, inherited from an asymptomatic parent in 2 cases, and inherited from an affected parent in 2 cases. Age of presentation ranged from 1 day-21 months. Five cases (38%) were diazoxide responsive. The remaining 7 cases were diazoxide unresponsive, and 5 had pancreatic surgery (3 near-total resection, 2 biopsies only) at ages 6 months-3 years. HK1 protein expression (IF) in islets of resected pancreas tissue from affected cases (n=5) was increased compared to control pancreas (n=2) and compared to surrounding acinar tissue. In RNA extracted from isolated islets (n=3), HK1 expression appeared to be increased in one case compared to control.

Conclusion: Non-coding variants in intron 2 of HK1 may represent over 5% of genetics negative HI cases. The clinical phenotype appears to be heterogenous, evidenced by variable age of presentation, diazoxide responsiveness, and pancreatectomy requirement. The hypothesis that these variants disrupt the normal suppression of HK1 expression in beta-cells is supported by IF staining in resected pancreatic tissue, but was not replicated by qPCR. Work is ongoing to elucidate the underlying mechanism by which these variants may result in HI.