Chromosome 17q12 microdeletions but not intragenic HNF1B mutations link developmental kidney disease and psychiatric disorder

Diabetes, Associated Clinical Spectrum, Long-term Prognosis, and Genotype/Phenotype Correlations in 201 Adult Patients With Hepatocyte Nuclear Factor 1B (HNF1B) Molecular Defects

OBJECTIVE

Molecular defects of hepatocyte nuclear factor 1B (HNF1B) are associated with a multiorgan disease, including diabetes (maturity-onset diabetes of the young 5) and kidney abnormalities. The HNF1B syndrome is related to HNF1B mutations or to a 17q12 deletion spanning 15 genes, including HNF1B. Here, we described HNF1B-related diabetes and associated phenotypes and assessed genotype/phenotype correlations at diagnosis and in the long-term.

RESEARCH DESIGN AND METHODS

This multicenter retrospective cohort study included 201 patients, aged 18 years or older at follow-up, with HNF1B mutations (n = 101) or deletion (n = 100).

RESULTS

Diabetes was present in 159 patients. At diagnosis, clinical symptoms of diabetes were present in 67 of 144 patients and HNF1B renal disease in 64 of 102. Although responsiveness to sulfonylureas/repaglinide was observed in 29 of the 51 tested, 111 of 140 patients (79%) were treated with insulin at follow-up. Diabetic retinopathy and/or neuropathy were present in 46 of 114 patients. Renal cysts were present in 122 of 166 patients, chronic kidney disease stages 3-4 (CKD3-4) in 75 of 169 (44%), and end-stage renal disease (ESRD) in 36 of 169 (21%). Compared with the patients with mutations, those with HNF1B deletion less often had CKD3-4/ESRD at diagnosis (11 of 43 vs. 27 of 35, P < 10^-4) and in the long term (40 of 78 vs. 71 of 91, P = 0.0003). They were leaner and more frequently treated with insulin.

CONCLUSIONS

In patients with HNF1B syndrome, diabetes complications, cardiovascular risk factors, CKD3-4, and ESRD are highly prevalent. At diabetes diagnosis, the presence of morphological and/or functional kidney disease may help etiological diagnosis. Genotype/phenotype correlations may have implications for the care and the prognosis of these patients.

Biliary Anomalies in Patients With HNF1B Diabetes

CONTEXT

The clinical spectrum of organogenetic anomalies associated with HNF1B mutations is heterogeneous. Besides cystic kidney disease, diabetes, and various other manifestations, odd cases of mainly neonatal and posttransplantation cholestasis have been described. The biliary phenotype is incompletely defined.

OBJECTIVE

To systematically characterize HNF1B-related anomalies in the bile ducts by imaging with magnetic resonance imaging (MRI) or magnetic resonance cholangiopancreatography (MRCP).

SETTING AND PATIENTS

Fourteen patients with HNF1B mutations in the catchment area of the Helsinki University Hospital were evaluated with upper abdominal MRI and MRCP. Blood samples and clinical history provided supplemental data on the individual phenotype.

MAIN OUTCOME MEASURE(S)

Structural anomalies in the biliary system, medical history of cholestasis, other findings in abdominal organs, diabetes and antihyperglycemic treatment, hypomagnesemia, and hyperuricemia.

RESULTS

Structural anomalies of the bile ducts were found in seven of 14 patients (50%). Six patients had choledochal cysts, which are generally considered premalignant.

CONCLUSIONS

Structural anomalies of the biliary system were common in HNF1B mutation carriers. The malignant potential of HNF1B-associated choledochal cysts warrants further studies.

Loss of transcriptional activation of the potassium channel Kir5.1 by HNF1β drives autosomal dominant tubulointerstitial kidney disease

Hepatocyte nuclear factor 1 homeobox B (HNF1β) is an essential transcription factor for the development and functioning of the kidney. Mutations in HNF1β cause autosomal dominant tubulointerstitial kidney disease characterized by renal cysts and maturity-onset diabetes of the young (MODY). Moreover, these patients suffer from a severe electrolyte phenotype consisting of hypomagnesemia and hypokalemia. Until now, genes that are regulated by HNF1β are only partially known and do not fully explain the phenotype of the patients. Therefore, we performed chIP-seq in the immortalized mouse kidney cell line mpkDCT to identify HNF1β binding sites on a genome-wide scale. In total 7,421 HNF1β-binding sites were identified, including several genes involved in electrolyte transport and diabetes. A highly specific and conserved HNF1β site was identified in the promoter of Kcnj16 that encodes the potassium channel Kir5.1. Luciferase-promoter assays showed a 2.2-fold increase in Kcnj16 expression when HNF1β was present. Expression of the Hnf1β p.Lys156Glu mutant, previously identified in a patient with autosomal dominant tubulointerstitial kidney disease, did not activate Kcnj16 expression. Knockdown of Hnf1β in mpkDCT cells significantly reduced the appearance of Kcnj16 (Kir5.1) and Kcnj10 (Kir4.1) by 38% and 37%, respectively. These results were confirmed in a HNF1β renal knockout mouse which exhibited downregulation of Kcnj16, Kcnj10 and Slc12a3 transcripts in the kidney by 78%, 83% and 76%, respectively, compared to HNF1β wild-type mice. Thus, HNF1β is a transcriptional activator of Kcnj16. Hence, patients with HNF1β mutations may have reduced Kir5.1 activity in the kidney, resulting in hypokalemia and hypomagnesemia.

Unraveling the genetic architecture of copy number variants associated with schizophrenia and other neuropsychiatric disorders

Recent studies show that the complex genetic architecture of schizophrenia (SZ) is driven in part by polygenic components, or the cumulative effect of variants of small effect in many genes, as well as rare single-locus variants with large effect sizes. Here we discuss genetic aberrations known as copy number variants (CNVs), which fall in the latter category and are associated with a high risk for SZ and other neuropsychiatric disorders. We briefly review recurrent CNVs associated with SZ, and then highlight one CNV in particular, a recurrent 1.6-Mb deletion on chromosome 3q29, which is estimated to confer a 40-fold increased risk for SZ. Additionally, we describe the use of genetic mouse models, behavioral tools, and patient-derived induced pluripotent stem cells as a means to study CNVs in the hope of gaining mechanistic insight into their respective disorders. Taken together, the genomic data connecting CNVs with a multitude of human neuropsychiatric disease, our current technical ability to model such chromosomal anomalies in mouse, and the existence of precise behavioral measures of endophenotypes argue that the time is ripe for systematic dissection of the genetic mechanisms underlying such disease. © 2016 Wiley Periodicals, Inc.