Clinical heterogeneity of abnormal glucose homeostasis associated with the HNF4A R311H mutation

We describe a diabetic child and her relatives carrying the HNF4A R311H mutation. The proband was diagnosed with insulin-dependent diabetes when 9.1 year-old. Three weeks later, a complete remission occurred. She underwent genetic testing showing the HNF4A-R311H mutation, which was found also in the brother (with impaired glucose tolerance), the mother (with gestational diabetes), and the maternal uncle (with type 2 diabetes). This case suggests that the HNF4A R311H mutation may play a role on hyperglycaemia since childhood and may be associated with clinical heterogeneity of abnormal glucose homeostasis. Transient diabetes might warrant the screening for MODY when indicated.


Findings
We describe a 10 years old diabetic girl recruited within a sample of MODY patients [6], Personal history: she is the first of two children born from non-consanguineous parents and was born full term and appropriate for gestational age after a pregnancy complicated by GDM. No transient congenital hyperinsulinism was detected [7]. She was healthy until the age of 9.1 years, when she was admitted to the local Hospital because of fainting. At admission, the following was recorded: blood glucose of 200 mg/dl; blood pressure, fundus oculi, heart ultrasound, electrocardiogram, blood biochemistry and pH were all normal; antithyroid and anti ß-cells antibodies were negative; finally, oral glucose tolerance test (OGTT) was consistent with DM (Table 1), with reduced insulin production (Matsuda Index 17.18, HOMA-IR 0.98, Insulinogenic Index −0.02, Disposition Index 0). Familial history was as follows: 40 years old healthy father; 35 years old mother, diagnosed as having GDM in both pregnancies (during pregnancies fasting blood glucose ranging from 110 to 140 mg/dl, blood glucose at 120′ of OGTT 597 mg/dl and 403 during the first and the second pregnancy, respectively); a 6 years old healthy brother; maternal grandmother and one out of 2 maternal uncles with type 2 DM which was diagnosed when he was 30 years old.
At admission, two IU of regular insulin at lunch and at dinner and a hypocaloric diet (BMI 24.1 kg/m 2 , 95th centile) were started. Three weeks later, body weight had dropped 1 kg and insulin injections were stopped because of recurrent hypoglycaemias. The patient was referred to our Unit 5 months later, still off of insulin. At that time, HbA1c was 40 mmol/mol and BMI 19.4 kg/m2 (75th centile). The HNF4A (NM_175914.4) gene analysis by PCR followed by direct sequencing showed the p.R311H c.932G > A variation in exon 8 (previously reported as p. R323H [8]). This mutation resides in the highly conserved extreme carboxy terminal domain [9] and causes a semiconservative aminoacid substitution predicted to be probably damaging by The Human Gene Mutation Database (http://www.hgmd.org) [10] and by PolyPhen-2 tool [11]. Genetic analysis was carried out also in first-degree relatives and in the maternal uncles, showing the same mutation in the mother, the brother, and the diabetic uncle. They underwent a comprehensive laboratory evaluation (Table 1). When 7.9 year-old, the brother underwent further examination showing impaired glucose tolerance (IGT) (baseline and after 120′ blood glucose and insulin:

Conclusions
HNF4A mutations lead to a progressive decrease of insulin secretion and hyperglycaemia [12] requiring oral hypoglycaemic drugs or insulin in most cases [13]. Our proband required low insulin dose (0.09 IU/ kg/day) only for few weeks. This transient course is puzzling and never described in HNF4A-MODY children so far. Likely, in the weeks before the diagnosis, some triggering factors played a role in deteriorating glucose homeostasis. As she became normoglycaemic and insulin free after some weight lost, we suggest that overweight may have played a major role, but we cannot exclude the role of other concomitant factors (stress or infectious diseases). Currently the proband, 11-year-old, is on normocaloric diet and presents a good glycaemic control (HbA1c 40 mmol/mol) without any hypoglycaemic treatment.
We did not perform any molecular study showing the effect of the mutation, so no direct effect can be postulated. However, we show that it segregates with hyperglycaemia, as it was found in the mother (GDM, currently normoglycaemic and normal weight), in the maternal uncle (type 2 DM onset at 30 years of age, currently overweight, diabetic and on hypoglycaemic diet), and in the brother (IGT). The same mutation was previously described in a 46 year-old obese man with type 2 DM and nephropathy [8]. Later, in the same position, a mutation with Arginine replaced by Cysteine (previously reported as p.R324C), was described in a 13 year-old Japanese MODY patient [14]. Unfortunately, no information about the families were reported in both cases, making impossible to speculate about any role of HNF4A-R311H on glucose homeostasis. To better assess its pathogenic role, we screened 198 non-diabetic individuals and 138 type 2 DM patients without family history of autosomal dominant inheritance of hyperglycaemia / diabetes and negative data were obtained.
The in silico analysis suggests that the R311H mutation causes a semiconservative aminoacid substitution predicted to be probably damaging [10,11]. Since some studies indicates a neutral [15], and others a deleterious [16] effect of such variation on HNF4A transcriptional activity, its biological role is controversial.
In conclusion, we report on a family with the HNF4A-R311H mutation cosegregating with heterogeneous phenotype of abnormal glucose homeostasis, including MODY1. The lack of a clear genotype-phenotype association requires great caution before considering this mutation causative of MODY1. We suggest that also transient DM warrants the screening for MODY in the presence of indicative family history, even if with clinical heterogeneity of abnormal glucose homeostasis.

Consent
Informed consent was obtained from the patient's parents for publication of this case report.

Competing interests
The authors declare that they have no competing interests.
Authors' contributions DM and RDP carried out the molecular genetic studies and participated in the sequence alignment. MD and VT participated in the clinical care and investigations of children and adults. MD and CM conceived the case report. VT, RDP, and MS coordinated and helped to draft the manuscript. MS and CM drafted the manuscript. All authors read and approved the final manuscript.