Gene: HNF1A (HGNC:11621)
Evidence Code: PVS1 — Very Strong
Modification Type: Strength
Use HNF1A PVS1 decision tree.




See below for adapted flowchart from ClinGen SVI group (Abou Tayoun, et al. 2018)


Variants generating PTCs 5’ of c.1714 of NM_000545.8, which includes the last 55 nucleotides of exon 9 and all of exon 10, are not expected to cause NMD (PMID: 24274751). The transactivation domain (TAD) of the protein overlaps with this region. The last 55 nucleotides of exon 9 (c.1714-1768) is enriched for disease-causing variants and loss-of function variants in this region have been found in patients/families with a MODY phenotype. Therefore, a “very strong” level of evidence will be used for loss-of-function variants 5’ of c.1768 regardless of where the premature termination codon occurs.


PVS1_Strong will be applied to nonsense variants at c.1803 (p.601) and 5’ and frameshift variants at c.1854 (p.618) and 5’. The distinction of nonsense and frameshift variants was made following a careful review of the phenotypes of individuals with loss-of-function variants in exon 10, which lead to our prediction that the addition of new amino acids from a frameshift will disrupt the TAD and cause a MODY phenotype more so than the deletion of a small part of the end of the TAD. Moderate phenotypic evidence was applied to the c.1802del (p.601Ter) variant, but the individual with the next nonsense variant (p.Gln625Ter) was unaffected. Frameshift variants at p.Ile618 and 5’ have been identified in patients with a phenotype consistent with MODY.






 “Exon skipping or use of a cryptic splice site that preserves reading frame” and “Single to multi-exon deletion that preserves reading frame”


Deletions of exon 1 would lead at least to loss of the initiation codon (see below for recommendations for initiation codon variants). Deletions of single exons 2, 3, 4, 5, 6, 8 or 9 all cause frameshift, and thus PVS1 would be used. In HNF1A, only exon 7 (LRG_522t1) is surrounded by introns of the same phase. Skipping or deletion of exon 7 would remove 64 amino acids in the TAD, which is >10% of the protein and 18% of the TAD. Given the significance of the TAD, we support still using PVS1 instead of PVS1_Strong in this situation. A deletion of exon 10 would remove part of the TAD but less than 10% of the protein. Since the TAD is critical to protein function, and variants that disrupt all of exon 10 have been found in patients with a MODY phenotype, we will use PVS1_Strong for deletions of exon 10 and splicing variants that would predict the skipping of exon 10. This specification is in accordance with Tayoun’s recommendation to use PVS1_Strong in cases in which the truncated region is critical to protein function.






Apply PVS1 to initiation codon variants. Four initiation codon variants have been identified in patients with a MODY phenotype. The closest potential in-frame start codon is p.Met118. Starting the protein at p.Met118 would remove 18% of the protein, including the entire dimerization domain. There are many P/LP variants upstream of p.Met118.


Per recommendations from the SVI, when RNA analysis demonstrates abnormal splicing from non-canonical splice site variants, apply PS3 instead of PVS1.