Hyperinsulinaemic Hypoglycaemia and Polycystic Kidney Disease - A Rare Case Concerning PMM2 Gene Pleiotropy.

Co-occurrence of hyperinsulinaemic hypoglycaemia and polycystic kidney disease (HIPKD) has been recently described. It is caused by a non-coding variant in the promoter region for phosphomannomutase 2 (PMM2), c.-167G>T, both in homozygous or compound heterozygous variants with deleterious coding. Although PMM2 has been associated with congenital disorder of glycosylation, patients do not present with this phenotype and have normal carbohydrate-deficient transferring testing. The authors present a rare case where specific PMM2 study was performed as a result of clinical suspicions. The patient was a 6-year-old female followed at our clinic due to congenital hyperinsulinism since she was 1 month old. She also presented with bilateral polycystic kidneys, detected in prenatal set, and simple hepatic cysts, for which she was treated with diazoxide and captopril. Initial metabolic and genetic studies were normal. PMM2 gene sequence study revealed the promotor variant c.-167G>T in compound heterozygosity with the previously described pathogenic variant c.422G>A (p.Arg141His), confirming the diagnosis of HIPKD. This is a notable case as it highlights the importance of keeping this diagnostic hypothesis in mind and serves as a reminder to perform proper clinical and genetic investigation. A correct, and early, diagnosis will avoid unnecessary additional investigations and will allow appropriate genetic counselling for this autosomal recessive disorder.

Prenatal Diagnosis and Management of a Fetal Goiter Hypothyroidism due to Dyshormonogenesis.

Fetal goiter is a rare disorder not expected to be found during a healthy woman's pregnancy. It can be a prenatal manifestation of congenital hypothyroidism due to thyroid dyshormonogenesis and it can lead to serious perinatal complications. A vascularized fetal neck mass was detected at 29 weeks' gestation of a healthy primigravida. Magnetic resonance was suggestive of goiter causing airway deviation without polyhydramnios. Maternal thyroid function was normal and thyroid antibodies were negative. Two intra-amniotic levothyroxine infusions were performed at 32 and 33 weeks. Serial imaging control showed no progression of the mass. Elective caesarean section was performed at 38 weeks. The male newborn was admitted to the intensive care unit due to cardiorespiratory insufficiency with pulmonary hypertension. Hormonal assays revealed primary congenital hypothyroidism and ultrasonography confirmed diffuse goiter. Levothyroxine was started. Currently, he is 6 years old with adequate growth and normal psychomotor development. Genetic study found a heterozygous mutation in the TPO gene.