rs193922485 — HNF1B

HNF1B and the Multisystem Glucose-Kidney Axis

The HNF1B gene (hepatocyte nuclear factor 1-beta) encodes a transcription factor that directs the embryonic development of the kidneys, pancreas, liver, urogenital tract, parathyroid, and parts of the brain. Unlike single-organ transcription factors, HNF1β is a master regulator whose influence spans multiple organ systems simultaneously — which is why HNF1B-related disease produces such a diverse and often confusing clinical picture. Pathogenic HNF1B variants cause renal cysts and diabetes syndrome¹¹ renal cysts and diabetes syndrome
Also called MODY5 (maturity-onset diabetes of the young type 5) or HNF1B-related disorder; OMIM 189907, a dominantly-inherited condition that combines early-onset diabetes with kidney abnormalities and a constellation of other organ-system findings.

The rs193922485 variant sits within intron 8 of HNF1B, four nucleotides upstream of the exon 9 splice acceptor site. Its ClinVar annotation NM_000458.4:c.1654-4G>A²² NM_000458.4:c.1654-4G>A
Plus-strand genomic: NC_000017.11:g.37687396C>T; the HNF1B gene is on the minus strand, so the coding-strand G>A corresponds to the plus-strand C>T reflects a position close enough to the splice junction that it was flagged as potentially significant — but computational splice prediction tools and the observation that this nucleotide is not conserved across vertebrate species have led the most recent high-volume clinical laboratories to classify it as likely benign. Three of six ClinVar submitters classify it as likely benign; three as uncertain significance. No published case series documents clinical HNF1B disease in an individual specifically carrying this variant.

The Mechanism

True pathogenic HNF1B variants disrupt haploinsufficiency — one functional copy of HNF1B is insufficient for normal organ development, causing developmental defects in the branching architecture of the kidneys, the differentiation of pancreatic cells (leading to reduced beta-cell mass and early-onset diabetes), magnesium reabsorption in the renal tubule (causing hypomagnesemia), and hepatocyte differentiation. The full syndrome includes renal cysts, early-onset non-immune diabetes, hypomagnesemia, pancreatic dysplasia, and urogenital malformations — often in combination, but rarely all in one individual.

Whether c.1654-4G>A disrupts splicing depends on whether the adenosine substitution at position -4 of the intron creates a novel splice branch point or weakens the polypyrimidine tract. Current in silico tools predict no significant effect on normal splicing at this position, and the non-conserved nucleotide context supports the likely benign interpretation. However, because the clinical consequence of a true splice disruption here would be significant, the variant warrants awareness, particularly in individuals who present with characteristic features of HNF1B-related disease.

The Evidence

HNF1B-related disease is well characterized at the gene level³³ well characterized at the gene level
Verhave JC et al. J Am Soc Nephrol 2016, PMID 26319241. A large cohort study of 61 confirmed MODY5 patients Ge Z et al. 2022⁴⁴ Ge Z et al. 2022
Front Endocrinol, PMID 35846334 found: renal cysts in 72%, hypomagnesemia in 92%, pancreatic dysplasia in 72%, median diabetes onset age of 16 years, and lean body habitus (only 8% overweight). Family history of diabetes was present in 66% — consistent with autosomal dominant inheritance. These data apply to confirmed pathogenic HNF1B variants; the clinical impact of this specific intronic variant is unknown.

The most common type of pathogenic HNF1B change (~40-50% of cases) is a recurrent whole-gene deletion at chromosome 17q12. Point mutations (missense, nonsense, and splice-site) account for the remainder. Intronic variants at the splice acceptor can be pathogenic if they disrupt the AG dinucleotide consensus or the polypyrimidine tract, but variants at position -4 (outside the core splice signal of the last two intronic nucleotides) require functional RNA evidence to confirm pathogenicity.

This specific variant has no published case reports linking it to confirmed HNF1B disease. Its clinical significance therefore remains technically unresolved.

Practical Actions

The primary clinical value of knowing about this variant is awareness: if you carry the T allele and have features consistent with HNF1B-related disease (unexplained renal cysts, early-onset non-immune diabetes, low magnesium, urogenital anomalies), this result supports requesting specialist evaluation and clinical-grade HNF1B testing. If you have none of these features, the variant is most likely benign based on current evidence.

Interactions

The HNF1B gene is the central axis for MODY5 / renal cysts and diabetes syndrome. Other MODY-causing genes (HNF1A for MODY3, HNF4A for MODY1, GCK for MODY2) cause clinically distinct subtypes that require different management — differentiating them requires genetic testing because treatment differs substantially. For blood sugar regulation, TCF7L2 rs7903146 and GCK variants operate in different pathways but converge on insulin secretion and glucose homeostasis.