Pseudohypoparathyroidism

This Consensus Statement covers recommendations for the diagnosis and management of patients with pseudohypoparathyroidism (PHP) and related disorders, which comprise metabolic disorders characterized by physical findings that variably include short bones, short stature, a stocky build, early-onset obesity and ectopic ossifications, as well as endocrine defects that often include resistance to parathyroid hormone (PTH) and TSH. The presentation and severity of PHP and its related disorders vary between affected individuals with considerable clinical and molecular overlap between the different types. A specific diagnosis is often delayed owing to lack of recognition of the syndrome and associated features. The participants in this Consensus Statement agreed that the diagnosis of PHP should be based on major criteria, including resistance to PTH, ectopic ossifications, brachydactyly and early-onset obesity. The clinical and laboratory diagnosis should be confirmed by a molecular genetic analysis. Patients should be screened at diagnosis and during follow-up for specific features, such as PTH resistance, TSH resistance, growth hormone deficiency, hypogonadism, skeletal deformities, oral health, weight gain, glucose intolerance or type 2 diabetes mellitus, and hypertension, as well as subcutaneous and/or deeper ectopic ossifications and neurocognitive impairment. Overall, a coordinated and multidisciplinary approach from infancy through adulthood, including a transition programme, should help us to improve the care of patients affected by these disorders.

Basal ganglia calcifications could be incidental findings up to 20% of asymptomatic patients undergoing CT or MRI scan. The presence of neuropsychiatric symptoms associated with bilateral basal ganglia calcifications (which could occur in other peculiar brain structures, such as dentate nuclei) identifies a clinical picture defined as Fahr's Disease. This denomination mainly refers to idiopathic forms in which no metabolic or other underlying causes are identified. Recently, mutations in four different genes (SLC20A2, PDGFRB, PDGFB, and XPR1) were identified, together with novel mutations in the Myogenic Regulating Glycosylase gene, causing the occurrence of movement disorders, cognitive decline, and psychiatric symptoms. On the other hand, secondary forms, also identified as Fahr's syndrome, have been associated with different conditions: endocrine abnormalities of PTH, such as hypoparathyroidism, other genetically determined conditions, brain infections, or toxic exposure. The underlying pathophysiology seems to be related to an abnormal calcium/phosphorus homeostasis and transportation and alteration of the blood-brain barrier.

Pseudohypoparathyroidism type 1a (PHP1a) is characterized by hypocalcaemia and hyperphosphatemia due to parathyroid hormone resistance, in association with the features of Albright's hereditary osteodystrophy (AHO). PHP1a is caused by maternally inherited inactivating mutations of Gs-alpha, which is encoded by a complex imprinted locus termed GNAS. Paternally inherited mutations can lead either to pseudopseudohypoparathyroidism (PPHP) characterized by AHO alone, or to progressive osseous heteroplasia (POH), characterized by severe heterotopic ossification. The clinical aspects and molecular genetics of PHP1a and its related disorders are reviewed together with the 343 kindreds with Gs-alpha germline mutations reported so far in the literature. These 343 (176 different) mutations are scattered throughout the 13 exons that encode Gs-alpha and consist of 44.9% frameshift, 28.0% missense, 14.0% nonsense, and 9.0% splice-site mutations, 3.2% in-frame deletions or insertions, and 0.9% whole or partial gene deletions. Frameshift and other highly disruptive mutations were more frequent in the reported 37 POH kindreds than in PHP1a/PPHP kindreds (97.3% vs. 68.7%, P < 0.0001). This mutation update and respective genotype-phenotype data may be of use for diagnostic and research purposes and contribute to a better understanding of these complex disorders.

ContextClinical presentation of inactivating parathyroid hormone (PTH)/PTH-related protein (PTHrP) signaling disorders (iPPSDs, historically pseudohypoparathyroidism [PHP]) exhibits pronounced age-dependence. Indeed, main features, including PTH resistance and brachydactyly (BD), develop during late childhood, while other features (ectopic ossifications, obesity, and hypothyroidism) are most prevalent in toddlers. The latter are included among minor diagnostic criteria; therefore, a substantial diagnostic delay has been reported.ObjectiveThe aim of this work is to describe the early natural history of a large cohort of iPPSD/PHP patients to improve diagnosis, with the final goal of proposing new diagnostic criteria for early infancy and reducing diagnostic delay.MethodsWe included 117 patients regularly followed up at 2 European endocrinology tertiary centers, and we retrospectively collected data on the age of onset of main clinical and hormonal features.ResultsIn our cohort the median age at diagnosis was 5.9 years. Age of onset of PTH resistance and BD, major criteria for diagnosis, was significantly different from that of both thyrotropin (TSH) resistance and obesity (median age 6.1, 5.8, 1.85, and 2 years, respectively). Minor diagnostic criteria were more represented than major criteria in children before age 2 years (P = .002). Indeed, in 64% of patients before age 2 years none of the major criteria were observed; conversely, 71% had already developed at least one minor criterion. In particular, 20% had developed TSH resistance and obesity.ConclusionThe clinical picture of iPPSD/PHP in early infancy differs from that of mid-late infancy and adults, thus current diagnostic criteria may not be appropriate for children. We suggest that the combination of early-onset obesity and elevated TSH should raise suspicion and trigger genetic screening before age 2 years.