Based on the findings from our studies and others reviewed here, it is possible to offer a practical approach for managing patients and families with FIHP, for which an obvious syndromic etiology has been excluded. Sporadic cases of HPT, on the other hand, must be evaluated according to standard recommendations. In the context of FIHP, the first step is to review the medical, dental and surgical history of the proband and all available affected members. This careful review should emphasize features of MEN1 (recurrent HPT, ulcers, and pituitary tumors), features of HPT-JT (parathyroid cancer, fibrous jaw tumors, kidney cysts or tumors), and features of FHH (unsuccessful parathyroid surgery, rare urolithiasis and possible hypermagnesemia in hypercalcemic members, and hypercal- cemia in cases below age 10).
If this focused review of systems is negative, the next step is to examine the renal calcium clearance-to-creatinine clearance ratio in all available hypercalcemic members. At the same time obtain blood calcium (preferably ionized) from as many untested first-degree relatives as possible, including young children in this process; any newly identified hypercalcemic members should also be checked for relative hypocalciuria. Imaging studies for gnathic and renal features of HPT-JT should be obtained on all hypercalcemic members at this point. Gene mutational testing to confirm or further exclude the incomplete expression of a syndromic form of familial HPT can then be pursued. Specific gene tests screening for CASR, MEN1 and HRPT2 mutation are all commercially available in CLIA-approved laboratories. CASR mutation testing can be sought early or late in the workup of the FIHP kindred. MEN1 mutation testing and periodic blood hormone testing for occult gastrinoma or prolactinoma may be worthwhile, particularly in FIHP patients who continue to appear non-syndromic. Similarly HRPT2 gene mutation testing and periodic orthopantography of the jaw and renal ultrasound can be considered in affected individuals from FIHP kindreds lacking syndromic features. If 7 or more affected members are available and the diagnosis is still uncertain, then genetic linkage could be pursued, focusing on loci for the known familial HPT syndromes on chromosomes 3q, 1q25-31, and 11q13. Because the number of affected family members is often small, a definitive syndromic diagnosis is often not possible. Such non-syndromic FIHP families should then be followed with each of the three main syndromic diagnoses in mind.
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