Hereditary hyperparathyroidism: Familial Isolated PHPT (FIHPT)

FIHPT (OMIM 145000) is a rare hereditary disorder characterized by uni- or multiglandular parathyroid lesions in the absence of hyperfunction in other endocrine tissues (Table I). FIHPT is transmitted in an autosomal dominant manner. Few large families have been shown to be linked to MEN1 gene, or to calcium sensing receptor (CaSR) gene mutations, while other families exhibit a segregation of phe- notype with DNA markers close by the Hyperparathyroidism- Jaw tumors (HPT-JT) syndrome locus at 1q25-q32. Most of FIHPT kindreds have currently an unknown genetic background (Table II). To date, approximately over 100 FIHPT families have been described.

In deed, the clinical management of this form could be complex, although the generic surgical principles of PHPT treatment can be generally applied.
Pathology

Unior multiglandular involvement represents the most frequent pathological picture underlying the parathyroid hyper- function (Table III). Progression to malignancy have not been reported for affected subjects with solitary parathyroid adenoma from two FIHPT families mapped to the same region as the HPT-JT syndrome on chromosome 1q21-q32.

Molecular aspects

No gene has yet been associated exclusively with FIHPT. However, as mentioned above, FIHPT has been linked to mutations in the MEN1, and CaSR genes, whereas in some families genetic linkage to these loci was not established. All this is consistent with a genetic and clinical heterogeneity of this form of PHPT. Carpten et al. reported in a patient from one of the two FIHPT families mapped to chromosome 1q21-q-32, a mutation in HRPT2 gene, confirming the they are allelic to the HPT-JT syndrome (Table III).

Treatment of FIHPT manifestations

In a case of uniglandular disease, parathyroid adenomectomy can be performed, whereas for multiglandular involvement a subtotal parathyroidectomy or total parathyroidectomy, with autologous reimplantation, can be considered (Table III). Of course, FIHPT linked to mutations in MEN1 or HRPT2 genes should be treated similarly to MEN1- and HPT-JT-associated PHPT, respectively, since the patient may be from a kindred with absent or low penetrance of other associated tumor types.
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