First Reported Use of Recombinant Parathyroid Hormone in Kenny–Caffey Syndrome Type 2: A Case Report and Literature Review

<b>Background/Objectives</b>: Hypoparathyroidism (HPT) is a disorder caused by the insufficient production of parathyroid hormone (PTH). Its main features include decreased serum calcium, increased serum phosphorus, and abnormal bone modeling. In children, HPT is most commonly due to genetic disorders. Among rare genetic syndromes that can include HPT in their clinical spectrum is Kenny-Caffey syndrome (KCS) type 2. Conventional therapy for HPT primarily consists of oral calcium and active vitamin D metabolites. The major limitation of conventional therapy is hypercalciuria with an increased risk of nephrocalcinosis. However, a subset of patients fails to achieve the desired therapeutic response to conventional treatment; the reasons for this remain incompletely understood in some cases. The failure to achieve therapeutic targets and persistent hypercalciuria are the main indications for considering therapy with recombinant human parathyroid hormone (rhPTH). <b>Methods:</b> In addition to the review of the literature on rhPTH use in pediatric hypoparathyroidism, the first application of rhPTH in the treatment of genetically caused HPT in a child with Kenny-Caffey syndrome type 2 (KCS2) was described. <b>Results:</b> In this paper, we present a two-month-old infant who received rhPTH for 14 months. A heterozygous <i>de novo</i> p.Ser541Pro variant in the <i>FAM111A</i> gene was identified through whole-genome sequencing, indicating a diagnosis of KCS2. A biological mechanism linking FAM111A protein function with a more profound disruption of parathyroid development or function was proposed, suggesting that rhPTH therapy may be particularly beneficial in KCS2 cases. <b>Conclusions:</b> This is the first reported use of rhPTH in a child in Serbia and the first reported use in KCS type 2. By reviewing the literature, we analyzed the conditions in which rhPTH has been used, dosing approaches and durations, requirements for concomitant conventional therapy during rhPTH treatment, and the effects of rhPTH on calciuria. We provide an overview of rhPTH use in children. Additionally, based on the pathogenic genetic variant responsible for KCS2 in our patient, we propose possible etiologic explanations. This work aims to encourage a consideration of rhPTH use in children following its official approval.