Digital clubbing, joint pain, and skin changes in a young man: primary hypertrophic osteoarthropathy

Two cases of primary hypertrophic osteoarthropathy caused by HPGD variants: a case report and literature review

BACKGROUND

Primary hypertrophic osteoarthropathy (PHO) is a rare genetic disorder primarily characterized by digital clubbing, pachydermia, and periostitis. The rarity of this disease often leads to misdiagnosis or delayed diagnosis.

METHODS

We describe the clinical and genetic findings of two pediatric PHO cases caused by HPGD variants and perform a systematic literature review of HPGD-related PHO cases.

RESULTS

Both patients exhibited congenital digital clubbing and patent ductus arteriosus from birth. Radiographs revealed cortical bone thickening and a periosteal reaction. Patient 1 displayed gait abnormalities and delayed cranial suture closure, while Patient 2 had bilateral leg swelling. Whole exome sequencing identified a compound heterozygous variant (NM_000860.6: c.189C > A, p.C63* and NM_000860.6: c.310_311delCT, p. L104Afs*3) in Patient 1 and a homozygous splice-site variant (NG_011689.1(NM_000860.6): c.324 + 5G > A) in Patient 2. All variants were classified as pathogenic based on the American College of Medical Genetics and Genomics criteria. Among 89 reviewed cases, the c.310_311delCT variant accounted for 37.1% (33/89), predominantly in homozygous form (60.6%, 20/33). The median urinary prostaglandin E2 (PGE2)-to-creatinine ratio in PHO patients was 627.1 ng/mmol (normal: 61.49 ng/mmol). Notably, the median age of symptom onset was 5.1 years, while diagnosis occurred at 22.1 years, with a male predominance (male-to-female ratio: 2.2:1).

CONCLUSION

We report the first HPGD c.189C > A variant, expanding the genetic spectrum of PHO. The c.310_311delCT variant represents a recurrent hotspot, predominantly in homozygosity. Our findings highlight the importance of early genetic testing and multidisciplinary management to reduce diagnostic delays and improve outcomes.

Reclassification of the HPGD p.Ala13Glu variant causing primary hypertrophic osteoarthropathy

Here, we highlight the case of a 31-yr-old man who had clinical features of primary hypertrophic osteoarthropathy (PHOAR) and harbored a homozygous variant (c.38C > A, p.Ala13Glu) in the HPGD gene, as indicated by whole-exome sequencing (WES). This variant has been previously classified by our laboratory as a variant of uncertain significance (VUS). However, another patient with the same phenotype and the same homozygous variant in HPGD was subsequently reported. In reassessing the variant, the absence of this variant in the gnomAD population database, supporting computational predictions, observation in homozygosity in two probands, and specificity of the phenotype for HPGD, all provide sufficient evidence to reclassify the HPGD c.38C > A, p.Ala13Glu variant as likely pathogenic.

Primary hypertrophic osteoarthropathy: genetics, clinical features and management

Primary hypertrophic osteoarthropathy (PHO) is a genetic disorder mainly characterized by clubbing fingers, pachydermia and periostosis. Mutations in the HPGD or SLCO2A1 gene lead to impaired prostaglandin E2 (PGE2) degradation, thus elevating PGE2 levels. The identification of the causative genes has provided a better understanding of the underlying mechanisms. PHO can be divided into three subtypes according to its pathogenic gene and inheritance patterns. The onset age, sex ratio and clinical features differ among subtypes. The synthesis and signaling pathways of PGE2 are outlined in this review. Cyclooxygenase-2 (COX-2) is the key enzyme that acts as the rate-limiting step for prostaglandin production, thus COX-2 inhibitors have been used to treat this disease. Although this treatment showed effective results, it has side effects that restrain its use. Here, we reviewed the genetics, clinical features, differential diagnosis and current treatment options of PHO according to our many years of clinical research on the disease. We also discussed probable treatment that may be an option in the future.

Primary pachydermoperiostosis associated with pigmented villonodular synovitis: An unknown association?

Primary pachydermoperiostosis is a rare genetic disease affecting the skin and musculoskeletal system. In contrast to secondary hypertrophic osteoarthropathy, primary pachydermoperiostosis is considered a benign condition. While a variety of associated abnormalities have been described in this form, any association with tumors was previously reported in the literature. We hereby describe the first case of a 20-year-old man with primary pachydermoperiostosis revealed by a knee synovial tumor.