Familial isolated primary hyperparathyroidism - a multiple endocrine neoplasia type 1 variant?

Objective: Familial isolated primary hyperparathyroidism (FIHP) is defined as hereditary primary hyperparathyroidism without the association of other diseases or tumors. Linkage analyses suggest that different genotypes can l ead to the same phenotype of primary hyperparathyroidism. Hereditary syndro mes associated with primary hyperparathyroidism are multiple endocrine neop lasia type 1 and type 2 (MEN 1 and MEN 2). In MEN 1. multiple parathyroid a denomas occur in more than 90% of the patients. Therefore, it has been sugg ested that FIHP could represent a variant or partial expression of MEN 1. Design: We report on a large FIHP kindred with a MEN1 gene mutation. Ninete en family members (aged 10 to 87 years) were screened. Furthermore. statist ical comparison by Fisher's exact tests of FIHP families with MEN1 gene mut ations and MEN 1 families with two or more endocrinopathies was carried out to investigate genotype-phenotype correlations. Methods: Mutational analysis of leucocyte DNA was carried out by direct seq uencing of the complete coding region of the MEN1 gene. Screening of MEN 1 manifestations was carried out by determination of serum calcium, phosphate , parathyroid hormone, prolactin. ACTH, cortisol, IGF-I, gastrin, glucose, insulin, glucagon. serum potassium, aldosterone, plasma renin and urinary h ydroxyindoleacetic acid. Results: We detected an in-frame deletion mutation in exon 8 of the MEN1 ge ne resulting in the deletion of one glutamine acid residue at position 363. It was found in eight individuals. Two of these family members (aged 42 an d 60 years) were operated for primary hyperparathyroidism, and three (aged 13 to 40 years) showed mild hypercalcemia and parathyroid hormone levels wi thin the upper normal range or slightly elevated, without any clinical symp toms. Two individuals (aged 12 and 19 years) were normocalcemic. One could not be tested. None of them had clinical evidence of other MEN 1 manifestat ions. Statistical comparison of the mutation types in families with FIHP an d families with two or more MEN 1-associated endocrinopathies reported in o ther studies reveals a significant difference. In families with FIHP missen se/in-frame mutations have been found in 87.5% of cases whereas in families with tumors in various endocrine glands these mutation types occur much le ss frequently (21-34%. P < 0.05). Conclusions: These studies indicate that FIHP can represent a partial MEN 1 variant and is often caused by missense/in-frame mutations.