A Hong Kong Chinese kindred with familial hypocalciuric hypercalcaemia caused by AP2S1 mutation
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Felix Chi Kin Wong1, Wai Sheung Wong2, Jeffrey Sung Shing Kwok1
1Department of Chemical Pathology, Prince of Wales Hospital, Shatin, Hong Kong.
Insights
Familial hypocalciuric hypercalcaemia (FHH) is a rare genetic disorder. This study identifies a novel AP2S1 gene mutation causing FHH type 3 in a Hong Kong Chinese family.
Area of Science:
- Genetics
- Endocrinology
- Calcium Homeostasis
Background:
- Familial hypocalciuric hypercalcaemia (FHH) is a genetic disorder affecting calcium regulation.
- Mutations in CASR, GNA11, and AP2S1 genes are known causes of FHH.
- FHH is characterized by hypercalcaemia and low urinary calcium excretion.
Observation:
- A Hong Kong Chinese family presented with hypercalcaemia unresponsive to parathyroidectomy.
- Genetic analysis excluded mutations in the CASR gene (FHH type 1).
- The proband, her brother, and niece exhibited hypercalcaemia.
Findings:
- A heterozygous c.43C>T (p.Arg15Cys) mutation in the AP2S1 gene was identified in the affected family members.
- This mutation confirmed the diagnosis of FHH type 3 (FHH3).
- This represents the first reported Chinese kindred with FHH3 caused by AP2S1 mutations.
Implications:
- This finding expands the spectrum of genetic causes for FHH.
- It highlights the importance of genetic testing for AP2S1 in diagnosing FHH, particularly in diverse ethnic populations.
- Accurate genetic diagnosis is crucial for appropriate patient management and genetic counseling.
Abstract:
Familial hypocalciuric hypercalcaemia (FHH) is a genetic disorder of altered calcium homeostasis. Mutations in the CASR, GNA11 and AP2S1 genes have been reported to cause FHH. We report a Hong Kong Chinese kindred with FHH type 3 (FHH3) caused by mutations in AP2S1. The proband, a 51-year-old woman with hypercalcaemia, was initially diagnosed to have primary hyperparathyroidism but repeated parathyroidectomy failed to normalize her plasma calcium concentrations. Later, FHH was suspected and yet no mutations were identified in the CASR gene which causes FHH type 1 (FHH1), the most common form of FHH. Genetic testing of AP2S1 revealed a heterozygous c.43C>T (p.Arg15Cys) mutation, confirming the diagnosis of FHH3. The elder brother and niece of the proband, who both have hypercalcaemia, were found to harbour the same mutation. To our knowledge, this is the first Chinese kindred of FHH3 reported in the English literature.
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