Clinical and Genetic Analysis of Multiple Endocrine Neoplasia Type 1-Related Primary Hyperparathyroidism in Chinese

Abstract

Objective: Multiple endocrine neoplasia type 1-related primary hyperparathyroidism (MHPT) differs in many aspects from sporadic PHPT (SHPT). The aims of this study were to summarize the clinical features and genetic background of Chinese MHPT patients and compare the severity of the disease with those of SHPT.

Design and methods: A total of 40 MHPT (27 sporadic, 7 families) and 169 SHPT cases of Chinese descent were retrospectively analyzed. X-rays and ultrasound were used to assess the bone and urinary system. Dual energy x-ray absorptiometry (DXA) were performed to measure bone mineral density (BMD). Besides direct sequencing of the MEN1 and CDKN1B genes, multiplex ligation-dependent probe amplification (MLPA) was used to screen gross deletion for the MEN1 gene.

Results: Compared with SHPT patients, MHPT patients showed lower prevalence of typical X-ray changes related to PHPT (26.3% vs. 55.7%, P = 0.001) but higher prevalence of urolithiasis/renal calcification (40.2% vs. 60.0%, P = 0.024). MHPT patients showed higher phosphate level (0.84 vs. 0.73mmol/L, P<0.05) but lower ALP (103.0 vs. 174.0U/L, P<0.001) and PTH (4.0 vs. 9.8×upper limit, P<0.001) levels than SHPT patients. There were no significant differences in BMD Z-scores at the lumbar spine and femoral neck between the two groups. Mutations in the MEN1 gene were detected in 27 MHPT cases. Among the nine novel mutations were novel, one of them involved the deletion of exon 5 and 6.

Conclusions: MHPT patients experienced more common kidney complications but less skeletal issues, and a milder biochemical manifestation compared with SHPT patients. MEN1 mutation detection rate was 79.4% and 9 of the identified mutations were novel.

Fig 1. Direct sequencing of eight novel MEN1 gene mutations.

Sequencing showing 8 germline heterozygous point mutations in MEN1 gene: (A) a missense mutation c.457 G>T (p.D153Y) in Family 6; (B) a frameshift mutation c.839_840 insT in Patient 14; (C) a frameshift mutation c.1061delG in Patient 16; (D) a missense mutation c.1117 C>G (p.P373A) in Patient 17; (E) a frameshift mutation c.313delC in Patient 20; (F) a splice site mutation c.1049+1 G>T in Patient 22; (G) a splice site mutation c.912+2 T>C in Patient 23; (H) a missense mutation c.848 T>C (p.L283P) in Patient 31.

Fig 2. Direct sequencing of the gross deletion mutation of the MEN1 gene in Family 3.

(A) In order to find the exact deletion site of the gross deletion mutation detected by MLPA (MEN1 del exon 5, 6), long-range PCR was used to amplify the region spanning exons 4–7 of the MEN1 gene. Compared with the fragment (WT: 1330bp) generated from the normal control (N), the two patients of Family 3 (I:2 and II:1) both carried an aberrant fragment (Mu: approximately 500bp). (B) DNA sequence analysis of the mutant PCR product revealed that it was 774bp (the lower one) smaller than the normal controls (the upper one). (C) The deletion breakpoints were 116bp downstream of exon 4 and 296bp upstream of exon 7 (MEN1 c.783+116_c.913-296del774).