Pseudohypoparathyroidism is a heterogeneous group of endocrine disorders characterized by end-organ resistance to parathyroid hormone, resulting in hypocalcemia, hyperphosphatemia, and inappropriately elevated parathyroid hormone levels despite normal kidney function. The underlying defect is not a shortage of parathyroid hormone but rather an impaired response to it in target tissues such as the kidneys and bones. Several recognized subtypes have been described, including type 1A, type 1B, type 1C, type 2, and the related condition pseudopseudohypoparathyroidism. These subtypes differ in their molecular basis, the parental origin of the underlying alteration, and their clinical features, with some forms also including features of Albright hereditary osteodystrophy such as short stature, a rounded face, and shortened bones in the hands and feet. The overall condition is rare, with an estimated prevalence of approximately 1 to 9 per 1,000,000 individuals.

The clinical features reflect both the consequences of low blood calcium and high blood phosphate and, in certain subtypes, additional skeletal and developmental findings. Hypocalcemia can lead to muscle cramps, tingling around the mouth and in the hands and feet, prolonged muscle contractions known as tetany, and in more severe cases seizures. Some individuals develop cataracts over time, and dental abnormalities have been reported. In type 1A and in pseudopseudohypoparathyroidism, features of Albright hereditary osteodystrophy are commonly observed, including short stature, a round face, obesity, shortening of certain bones in the hands and feet (most often the fourth and fifth metacarpals), subcutaneous ossifications, and in some individuals cognitive or learning differences. In type 1A, resistance can extend beyond parathyroid hormone to other hormones that signal through the same pathway, leading to hypothyroidism due to thyroid stimulating hormone resistance, reproductive hormone abnormalities, and growth hormone deficiency in some individuals. Type 1B is more often limited to parathyroid hormone resistance and typically lacks the skeletal features of Albright hereditary osteodystrophy. Symptoms of pseudohypoparathyroidism can overlap with other conditions. Genetic testing is required to confirm the diagnosis and distinguish it from conditions with similar presentations. Not all individuals experience all features, and severity varies considerably.

Pseudohypoparathyroidism is caused by alterations affecting a key signaling protein that connects many hormone receptors, including the parathyroid hormone receptor, to their intracellular response. The locus encoding this protein is subject to genomic imprinting, a phenomenon where gene expression depends on whether the gene is inherited from the mother or father. Because of this parent of origin regulation, the same molecular change can produce different clinical conditions depending on which parental copy is affected and how it is altered. Type 1A and type 1C result from loss of function variants on the maternally inherited allele and lead to combined hormone resistance and the skeletal features of Albright hereditary osteodystrophy. Type 1B is caused by loss of normal methylation marks at differentially methylated regions at this locus, disrupting parent specific gene expression in tissues such as the kidney; type 1B can occur sporadically or be inherited. Pseudopseudohypoparathyroidism arises from loss of function variants on the paternally inherited allele and produces the skeletal features of Albright hereditary osteodystrophy without significant hormone resistance. Type 2 is less well characterized at the molecular level. Because each subtype involves a different molecular mechanism and different parent of origin effects, recurrence risk depends on the underlying molecular mechanism and on which parent carries the alteration, and is not described by a single percentage. Genetic counseling is strongly recommended to discuss the specific subtype and options for prenatal and family testing.

Diagnosis begins with biochemical evaluation showing the characteristic combination of low serum calcium, elevated serum phosphate, and elevated parathyroid hormone in the setting of normal kidney function and adequate vitamin D status. Additional endocrine testing typically assesses thyroid stimulating hormone, free thyroxine, and reproductive and growth hormones, since multiple hormone resistances may occur in some subtypes. Imaging of the hands, feet, and skeleton can identify shortening of specific bones, advanced bone age, and subcutaneous ossifications consistent with Albright hereditary osteodystrophy. Molecular and epigenetic testing is essential to confirm the diagnosis and distinguish among subtypes. Methylation analysis at the relevant differentially methylated regions is a first line investigation for many cases, particularly type 1B, where loss of normal methylation patterns is the underlying defect. Targeted sequencing for coding variants is used when an Albright hereditary osteodystrophy phenotype or combined hormone resistance suggests type 1A, type 1C, or pseudopseudohypoparathyroidism, and family based testing can help establish the parental origin of an identified variant. Symptoms can overlap with other conditions including primary hypoparathyroidism, vitamin D deficiency, and other syndromes featuring brachydactyly. Genetic testing is required to confirm the diagnosis and distinguish it from conditions with similar presentations.

Management focuses on correcting the metabolic disturbances, addressing additional hormone deficiencies when present, and providing multidisciplinary care for the broader features of the condition. Foundational treatment includes oral calcium supplementation together with an activated form of vitamin D to restore serum calcium toward normal and to lower elevated parathyroid hormone toward the upper limit of the normal range, while monitoring urinary calcium to limit the risk of kidney complications. Dietary phosphate restriction may be considered when phosphate levels remain persistently elevated. When other hormone resistances are identified, generic replacement therapies such as thyroid hormone replacement and hormonal support for reproductive or growth hormone deficiencies are tailored to the individual subtype. Care is typically coordinated by an endocrinologist and may also involve clinical genetics, orthopedics, ophthalmology, and developmental specialists. Regular surveillance is an essential part of long term care, helping to identify potential complications before they become serious, including periodic monitoring of calcium, phosphate, parathyroid hormone, thyroid function, growth, pubertal development, and bone health. Genetic counseling is recommended to discuss the specific molecular mechanism, parent of origin effects, and family planning options. Patients should discuss treatment options with their healthcare team to determine which therapies may be appropriate for their specific situation.

With consistent treatment and monitoring, most individuals with pseudohypoparathyroidism can lead full and productive lives. The metabolic abnormalities are generally manageable when calcium and active vitamin D therapy are carefully balanced and adjusted over time, and additional hormone deficiencies can usually be addressed with appropriate replacement therapy. The long term course depends on the specific subtype, the range of hormone systems involved, and the presence and severity of skeletal or developmental features. Some individuals experience few systemic effects beyond hypocalcemia, while others, particularly those with type 1A, may require lifelong attention to multiple endocrine systems and supportive care for features of Albright hereditary osteodystrophy. Modern endocrine care and structured surveillance have improved outcomes.

Active research focuses on improving diagnostic precision, deepening the understanding of imprinting biology at the underlying locus, and developing more targeted approaches for specific subtypes. Areas of investigation include refining methylation based testing to better distinguish among forms of the condition, characterizing the natural history of each subtype, and exploring therapies aimed at the skeletal and growth related features of Albright hereditary osteodystrophy. Several clinical studies are underway, including academic led investigations of growth hormone therapy in individuals with type 1A and Albright hereditary osteodystrophy and other studies evaluating supportive and metabolic interventions. Individuals interested in clinical trials can search ClinicalTrials.gov or consult their care team about eligibility.