Mutation in the HPGD gene encoding NAD+ dependent 15-hydroxyprostaglandin dehydrogenase underlies isolated congenital nail clubbing (ICNC)

Pediatric Nail Disorders

Background

Pediatric nail disorders encompass a broad range of conditions. This article aimed to consolidate current knowledge on pediatric nail disorders to enhance diagnostic proficiency and clinical management among healthcare professionals.

Summary

Pediatric nail disorders present a diagnostic challenge due to their diverse nature. Non-syndromic congenital nail disorders encompass various anomalies such as anonychia/hyponychia, congenital malalignment of the great toenail, and racket thumbs, each with distinct clinical presentations and genetic associations. Syndromic congenital nail disorders, often part of complex syndromes, are characterized by unique features and associated abnormalities. Acquired nail diseases in children, like Beau's lines and onychomadesis, typically result from trauma or infection, while melanonychia, although rare in children, requires careful monitoring for potential malignant alterations, with consideration for biopsy in cases with concerning features.

Key Messages

(1) Pediatric nail disorders may pose diagnostic challenges and require a comprehensive understanding of nail anatomy and development. (2) Congenital nail disorders encompass isolated anomalies and syndromic associations, necessitating thorough evaluation for associated systemic conditions. (3) Acquired nail diseases may indicate underlying trauma or systemic illness and require careful assessment.(4) Melanonychia in children requires ongoing monitoring and evaluation, emphasizing the importance of consistent follow-up and histopathological examination when necessary.

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.

Homozygous Missense Variant in the Solute Carrier Organic Anion Transporter 2A1 (SLCO2A1) Gene Underlies Isolated Nail Clubbing

BACKGROUND

Inherited isolated nail clubbing is a very rare Mendelian condition in humans, characterized by enlargement of the terminal segments of fingers and toes with thickened nails. Mutations in two genes have been reported to cause isolated nail clubbing in humans, which are the SLCO2A1 gene and the HPGD gene.

OBJECTIVES

An extended Pakistani family having two affected siblings born of unaffected consanguineous union was included in the study. Predominant isolated congenital nail clubbing (ICNC) without any other systemic abnormalities was observed, which we aimed to characterize at clinico-genetic level.

METHODS

Whole exome coupled with Sanger sequencing were employed to uncover the sequence variant as a cause of the disease. Furthermore, protein modeling was carried out to reveal the predicted possible effect of the mutation at the protein level.

RESULTS

Whole exome sequencing data analysis revealed a novel biallelic sequence variant (c.155T>A; p.Phe52Tyr) in the SLCO2A1 gene. Further, Sanger sequencing analysis validated and confirmed the segregation of the novel variant in the entire family. Subsequently, protein modeling of the wild-type and mutated SLCO2A1 revealed broad-scale change, which might compromise the proteins' secondary structure and function.

CONCLUSION

The present study adds another mutation to the SLCO2A1-related pathophysiology. The involvement of SLCO2A1 in the pathogenesis of ICNC may open exciting perceptions of this gene in nail development/morphogenesis.

Assessment score for the diagnosis of a case with pleuroparenchymal fibroelastosis

Idiopathic pleuropulmonary fibroelastosis is an extremely rare lung disease characterized by the combination of fibrosis of the visceral pleura and the fibroelastotic changes transcending in the subpleural lung parenchyma that predominantly affects the upper lobes with accompanying volume loss. It is mostly idiopathic while infection, autoimmunity, bone marrow or lung transplantation and genetic predisposition may be associated with the development of PPFE. The disease is exceptionally rare as approximately ninety cases have been reported in the literature currently. A 35-year-old female presented with exertional dyspnea, dry cough and weight loss. Physical examination demonstrated platythorax, suprasternal notch deepening and fine rales over the upper lobes. Blood count, serum biochemistry, autoimmunity and serologic markers for collagen vascular diseases were within normal limits. Arterial blood gases demonstrated a low pO2 (48 mm Hg) and a high pCO2 (54 mm Hg) values. Chest x-ray showed bilateral parenchymal fibrotic lesions, left pneumothorax, bronchiectasis in the middle and pleural thickening in the upper lung zones while HRCT revealed bilateral apical pleural thickening, traction bronchiectasis, subpleural reticulations, ground-glass opacities and honeycombing in the upper lobes. Bronchoscopy, BAL cytology, smear and culture did not reveal any pathologic findings. Relevant with the clinical, laboratory, radiologic manifestations and the differential diagnosis with other interstitial lung diseases, PPFE was the final diagnosis. The aim of this case report was to present the clinical manifestations of our case. The second crucial objective was to establish a diagnostic scoring system relevant with the literature and the clinical manifestations of the patient.

Digital clubbing as the predominant manifestation of hypertrophic osteoarthropathy caused by pathogenic variants in HPGD in three Indian families

15-Hydroxyprostaglandin dehydrogenase is NAD-dependent catalytic enzyme involved in prostaglandin biosynthesis pathway encoded by HPGD. The pathogenic variations in HPGD cause primary hypertrophic osteoarthropathy (PHO). The objective of the present study is to identify the genetic basis in patients with digital clubbing due to PHO. We performed detailed clinical and radiographic evaluation and exome sequencing in patients from three unrelated Indian families with PHO. Exome sequencing revealed two novel, c.34G>A (p.Gly12Ser) and c.313C>T (p.Gln105*) and a known variant, c.418G>C (p.Ala140Pro) in HPGD. Herein, we add three Indian families to HPGD mutation spectrum and review the literature on variants in this gene.

The first case of primary hypertrophic osteoarthropathy with soft tissue giant tumors caused by HPGD loss-of-function mutation

BACKGROUND

Primary hypertrophic osteoarthropathy (PHO) is a rare genetic multi-organic disease characterized by digital clubbing, periostosis and pachydermia. Two genes, HPGD and SLCO2A1, which encodes 15-hydroxyprostaglandin dehydrogenase (15-PGDH) and prostaglandin transporter (PGT), respectively, have been reported to be related to PHO. Deficiency of aforementioned two genes leads to failure of prostaglandin E2 (PGE2) degradation and thereby elevated levels of PGE2. PGE2 plays an important role in tumorigenesis. Studies revealed a tumor suppressor activity of 15-PGDH in tumors, such as lung, bladder and breast cancers. However, to date, no HPGD-mutated PHO patients presenting concomitant tumor has been documented. In the present study, we reported the first case of HPGD-mutated PHO patient with soft tissue giant tumors at lower legs and evaluated the efficacy of selective COX-2 inhibitor (etoricoxib) treatment in the patient.

METHODS

In this study, we summarized the clinical data, collected the serum and urine samples for biochemical test and analyzed the HPGD gene in our patient.

RESULTS

A common HPGD mutation c.310_311delCT was identified in the patient. In addition to typical clinical features (digital clubbing, periostosis and pachydermia), the patient demonstrated a new clinical manifestation, a giant soft tissue tumor on the left lower leg which has not been reported in HPGD-mutated PHO patient before. After 6-month treatment with etoricoxib, the patient showed decreased PGE2 levels and improved PHO-related symptoms. Though the soft tissue tumor persisted, it seemed to be controlled under the etoricoxib treatment.

CONCLUSION

This finding expanded the clinical spectrum of PHO and provided unique insights into the HPGD-mutated PHO.

Novel SLCO2A1 mutations cause gender differentiated pachydermoperiostosis

Primary hypertrophic osteoarthropathy (PHO) is a rare familial disorder with reduced penetrance for females. The genetic mutations associated with PHO have been identified in HPGD and SLCO2A1 which involved in prostaglandin E2 metabolism. Here we report 5 PHO patients from 4 non-consanguineous families. Two heterozygous mutations in solute carrier organic anion transporter family member 2A1 (SLCO2A1) were identified in two brothers by whole-exome sequencing. Three heterozygous mutations and 1 homozygous mutation were identified in other 3 PHO families by Sanger sequencing. However, there was no mutation in HPGD. These findings confirmed that homozygous or compound heterozygous mutations of SLCO2A1 were the pathogenic cause of PHO. A female individual shared the same mutations in SLCO2A1 with her PHO brother but did not have any typical PHO symptoms. The influence of sex hormones on the pathogenesis of PHO and its implication were discussed.

A novel mutation in the HPGD gene causing primary hypertrophic osteoarthropathy with digital clubbing in a Pakistani family

Primary hypertrophic osteoarthropathy (PHO) is a congenital multisystemic entity characterized by three major clinical symptoms: pachydermia, periostosis, and digital clubbing. Recently it has been reported that pathogenic mutations in two genes are known to be associated with PHO: HPGD and SLCO2A1. In the present study, a five-generation consanguineous Pakistani family harboring primary hypertrophic osteoarthropathy in autosomal-recessive pattern was ascertained. Whole genome single nucleotide polymorphisms (SNPs) genotyping and sequence analysis revealed a novel homozygous missense mutation (c.577T˃C) of the human HPGD gene in all affected members of the family. The study presented here demonstrate the first case of primary hypertrophic osteoarthropathy reported in Pashtun population.

Genetics of syndromic and non-syndromic hereditary nail disorders

The nail is a unique epithelial skin appendage made up of a fully keratinized nail plate. The nail can be affected in several systemic illnesses, dermatological diseases, and inherited nail disorders. Nail dystrophies can present as isolated disorders or as a part of syndromes. Substantial progress has been achieved in the management and diagnosis of nail diseases; however, not much is known about the underlying molecular controls of nail growth. The homeostasis and development of the nail appendage depend on the intricate interactions between the epidermis and underlying mesenchyme, and comprise different signaling pathways such as the WNT signaling pathway. Digit-tip regeneration in mice and humans has been a known fact for the past six decades; however, only recently the underlying biological mechanisms by which the nail organ achieves digit regeneration have been elucidated. Moreover, significant progress has been made in identifying nail stem cells and localizing stem cell niches in the nail unit. More fascinating, however, is the role they play in orchestrating the processes that lead to the regeneration of the digit. Further elucidating the role of nail stem cells and the signaling pathways driving epithelial-mesenchymal interactions in the nail unit might contribute to the development of novel therapeutic tools for amputees.

Clubbing and hypertrophic osteoarthropathy: insights in diagnosis, pathophysiology, and clinical significance

BACKGROUND

Digital clubbing and hypertrophic osteoarthropathy (HOA) form a diagnostic challenge. Subtle presentations of clubbing are often missed. The underlying pathophysiology remains unclear. Establishing a differential diagnosis based on nonspecific signs can be cumbersome. Finally, the prognostic value of clubbing and HOA remains unclear.

OBJECTIVE

This article reviews clinical criteria and pathophysiology of clubbing and HOA. A diagnostic algorithm is proposed, based on etiology and current insights. The prognostic impact on associated diseases is discussed.

METHODS

The Internet databases Medline and Embase were searched. Articles were selected based on relevance of abstract, article type and impact of the journal.

RESULTS

Diagnostic criteria include Lovibond's profile sign, distal/interphalangeal depth ratio and Schamroth's sign. Three pathophysiological causes of clubbing can be distinguished: hypoxia, chronic inflammation and aberrant vascularization. A prominent role for vascular endothelial growth factor is suggested. Associated symptoms and clinical signs should guide the initial diagnostic evaluation. Finally, clubbing is a negative prognostic factor in certain pulmonary disorders, including cystic fibrosis.

A Common Mutation and a Novel Mutation in the HPGD Gene in Nine Patients with Primary Hypertrophic Osteoarthropathy

Primary hypertrophic osteoarthropathy (PHO) is a hereditary bone disease characterized by digital clubbing, periostosis, and pachydermia. The HPGD gene encoding 15-prostaglandin dehydrogenase and SLCO2A1 encoding one type of prostaglandin transporter were found to be responsible for PHO. Mutations of either gene would lead to increased level of prostaglandin E2 (PGE2), which might contribute to the constellation of the symptoms. The aim of the study was to analyze the HPGD gene and the clinical characteristics in nine patients with the diagnosis of PHO. Nine patients, (eight males and one female) including two siblings and seven sporadic cases, were enrolled in the study. Clinical features were summarized, and blood and urine samples were collected. Sanger method was used to sequence the HPGD gene to detect mutations. Urinary PGE2 and prostaglandin metabolite (PGE-M) levels for each patient were measured and compared to the healthy controls. A recurrent c.310_311delCT mutation was identified in all patients, of which six were homozygous, two were heterozygous, and one was compound heterozygous with this mutation and a novel heterozygous missense mutation c.488G>A (p.R163H). The levels of PGE2 in urine were much higher than normal in all patients, along with lower PGE-M levels. In conclusion, nine PHO patients were characterized by typical clinical manifestations including digital clubbing, periostosis, and pachydermia. A common mutation and a novel mutation in HPGD gene were identified to be responsible for the disease, and c.310_311delCT mutation is likely to be a hot-spot mutation site for Asian PHO patients.

Genetics of human isolated hereditary nail disorders

Human hereditary nail disorders constitute a rare and heterogeneous group of ectodermal dysplasias. They occur as isolated and/or syndromic ectodermal conditions where other ectodermal appendages are also involved, and can occur associated with skeletal dysplasia. 'Nail disorder, nonsyndromic congenital' (OMIM; Online Mendelian Inheritance in Man) is subclassified into 10 different types. The underlying genes identified thus far are expressed in the nail bed and play important roles in nail development and morphogenesis. Here, we review the current literature on nail disorders and present a coherent review on the genetics of nail disorders. This review will pave the way to identifying putative genes and pathways involved in nail development and morphogenesis.

Nail abnormalities associated with systemic pathologies

Nail abnormalities can arise in conjunction with or as a result of systematic pathologies. These pathologies include single-organ diseases, multisystemic diseases, and drug-induced insults. Clinical signs associated with these conditions include dyschromias, vascular alterations, periungual tissue changes, textural dystrophies, contour alterations, and growth-rate alterations. The associated systemic pathologies may affect any part of the nail apparatus, including the nail matrix, the nail plate, the nail bed, the underlying vasculature, and the periungual tissues. The anatomical location and extent of damage determine the clinically manifested anomaly.

Mutations in the SLCO2A1 gene and primary hypertrophic osteoarthropathy: a clinical and biochemical characterization

CONTEXT

We previously demonstrated that deficiency of the prostaglandin transporter (SLCO2A1) is a cause of primary hypertrophic osteoarthropathy (PHO). However, its clinical and metabolic characteristics have not been well defined.

OBJECTIVE

The objective of the study was to expand this mutational spectrum to better delineate the SLCO2A1 deficiency phenotype and investigate the clinical and metabolic characteristics of a cohort of subjects with PHO.

DESIGN, SETTING, PATIENTS, AND MAIN OUTCOME MEASURE

Eleven affected individuals and their available healthy family members from 9 unrelated Chinese families with PHO (7 of which were previously undescribed) were clinically studied. The SLCO2A1 gene was screened and analyzed. Urinary levels of prostaglandin E₂ (PGE₂) and prostaglandin E metabolite (PGE-M) were measured using competitive ELISAs. The serum levels of total T, estradiol, sex hormone-binding protein, LH, FSH, and fasting gastrin were detected.

RESULTS

Nine different SLCO2A1 mutations were identified in affected individuals in the 7 previously undescribed families, 7 of which (Glu165X, Ala286GlnfsX35, Gln356AlafsX77, Gly369Asp, Gly379Glu, Glu465Lys, and c.861+2T>C) were novel. The urinary levels of PGE₂ and PGE-M were much higher in the SLCO2A1-deficient individuals and decreased with age. There was no relationship between sex hormones and PGE₂ or PGE-M. There was no significant difference in the levels of fasting serum gastrin between PHO patients with watery diarrhea and their relatives.

CONCLUSIONS

The present findings broaden the allelic spectrum of SLCO2A1 mutations. The urinary levels of PGE₂ and PGE-M in the SLCO2A1-deficient individuals decreased with age. The measurement of the excreted PGE₂ and PGE-M may have implications in the differential diagnosis, treatment, and follow-up of PHO.

Digital clubbing

Digital clubbing is an ancient and important clinical signs in medicine. Although clubbed fingers are mostly asymptomatic, it often predicts the presence of some dreaded underlying diseases. Its exact pathogenesis is not known, but platelet-derived growth factor and vascular endothelial growth factor are recently incriminated in its causation. The association of digital clubbing with various disease processes and its clinical implications are discussed in this review.

Identification of mutations in the prostaglandin transporter gene SLCO2A1 and its phenotype-genotype correlation in Japanese patients with pachydermoperiostosis

BACKGROUND

Pachydermoperiostosis (PDP) is a rare genetic disorder characterized by 3 major symptoms: pachydermia including cutis verticis gyrata (CVG), periostosis, and finger clubbing. Recently, a homozygous mutation in the gene HPGD, which encodes 15-hydroxyprostaglandin dehydrogenase (15-PGDH), was found to be associated with PDP. However, mutations in HPGD have not been identified in Japanese PDP patients.

OBJECTIVE

We aimed to identify a novel responsible gene for PDP using whole exome sequencing by next-generation DNA sequencer (NGS).

METHODS

Five patients, including 2 patient-parent trios were enrolled in this study. Entire coding regions were sequenced by NGS to identify candidate mutations associated with PDP. The candidate mutations were subsequently sequenced using the Sanger method. To determine clinical characteristics, we analyzed histological samples, as well as serum and urinary prostaglandin E2 (PGE2) levels for each of the 5 PDP patients, and 1 additional patient with idiopathic CVG.

RESULTS

From initial analyses of whole exome sequencing data, we identified mutations in the solute carrier organic anion transporter family, member 2A1 (SLCO2A1) gene, encoding prostaglandin transporter, in 3 of the PDP patients. Follow-up Sanger sequencing showed 5 different SLCO2A1 mutations (c.940+1G>A, p.E427_P430del, p.G104*, p.T347I, p.Q556H) in 4 unrelated PDP patients. In addition, the splice-site mutation c.940+1G>A identified in 3 of 4 PDP patients was determined to be a founder mutation in the Japanese population. Furthermore, it is likely that the combination of these SLCO2A1 mutations in PDP patients is also associated with disease severity.

CONCLUSION

We found that SLCO2A1 is a novel gene responsible for PDP. Although the SLCO2A1 gene is only the second gene discovered to be associated with PDP, it is likely to be a major cause of PDP in the Japanese population.

Mutations in the prostaglandin transporter encoding gene SLCO2A1 cause primary hypertrophic osteoarthropathy and isolated digital clubbing

Digital clubbing is usually secondary to different acquired diseases. Primary hypertrophic osteoarthropathy (PHO) is a rare hereditary disorder with variable digital clubbing as the most prominent feature, subperiosteal new bone formation, and arthropathy. Recently, mutations in the 15-hydroxy-prostaglandin dehydrogenase (15-PGDH) encoding gene HPGD were found to cause PHO. Here, we identified three unrelated families with different mutations in the prostaglandin transporter (PGT) encoding gene SLCO2A1 which presumably result in reduced metabolic clearance by 15-PGDH due to diminished cellular uptake of prostaglandin E(2) (PGE(2)) by mutant PGT. In two consanguineous families, homozygous mutations, an intragenic deletion that results in frameshift and a missense mutation, are associated with a severe PHO phenotype. In a third family, a heterozygous carrier of a stop mutation presents with isolated digital clubbing. Thus, our study further supports the importance of PGE(2) metabolism in the pathogenesis of digital clubbing and PHO.

Exome sequencing identifies SLCO2A1 mutations as a cause of primary hypertrophic osteoarthropathy

By using whole-exome sequencing, we identified a homozygous guanine-to-adenine transition at the invariant -1 position of the acceptor site of intron 1 (c.97-1G>A) in solute carrier organic anion transporter family member 2A1 (SLCO2A1), which encodes a prostaglandin transporter protein, as the causative mutation in a single individual with primary hypertrophic osteoarthropathy (PHO) from a consanguineous family. In two other affected individuals with PHO from two unrelated nonconsanguineous families, we identified two different compound heterozygous mutations by using Sanger sequencing. These findings confirm that SLCO2A1 mutations inactivate prostaglandin E(2) (PGE(2)) transport, and they indicate that mutations in SLCO2A1 are the pathogenic cause of PHO. Moreover, this study might also help to explain the cause of secondary hypertrophic osteoarthropathy.

Nrk2b-mediated NAD+ production regulates cell adhesion and is required for muscle morphogenesis in vivo: Nrk2b and NAD+ in muscle morphogenesis

Cell-matrix adhesion complexes (CMACs) play fundamental roles during morphogenesis. Given the ubiquitous nature of CMACs and their roles in many cellular processes, one question is how specificity of CMAC function is modulated. The clearly defined cell behaviors that generate segmentally reiterated axial skeletal muscle during zebrafish development comprise an ideal system with which to investigate CMAC function during morphogenesis. We found that Nicotinamide riboside kinase 2b (Nrk2b) cell autonomously modulates the molecular composition of CMACs in vivo. Nrk2b is required for normal Laminin polymerization at the myotendinous junction (MTJ). In Nrk2b-deficient embryos, at MTJ loci where Laminin is not properly polymerized, muscle fibers elongate into adjacent myotomes and are abnormally long. In yeast and human cells, Nrk2 phosphorylates Nicotinamide Riboside and generates NAD+ through an alternative salvage pathway. Exogenous NAD+ treatment rescues MTJ development in Nrk2b-deficient embryos, but not in laminin mutant embryos. Both Nrk2b and Laminin are required for localization of Paxillin, but not beta-Dystroglycan, to CMACs at the MTJ. Overexpression of Paxillin in Nrk2b-deficient embryos is sufficient to rescue MTJ integrity. Taken together, these data show that Nrk2b plays a specific role in modulating subcellular localization of discrete CMAC components that in turn plays roles in musculoskeletal development. Furthermore, these data suggest that Nrk2b-mediated synthesis of NAD+ is functionally upstream of Laminin adhesion and Paxillin subcellular localization during MTJ development. These results indicate a previously unrecognized complexity to CMAC assembly in vivo and also elucidate a novel role for NAD+ during morphogenesis.

Common and recurrent HPGD mutations in Caucasian individuals with primary hypertrophic osteoarthropathy

OBJECTIVE

Homozygous recessive germline mutations of the 15-hydroxyprostaglandin dehydrogenase (HPGD) gene, encoding 15-hydroxyprostaglandin dehydrogenase, result in persistent elevation of circulating PGE(2) levels, causing the syndrome of primary hypertrophic osteoarthropathy (PHO). Homozygous HPGD mutations have so far been reported in 10 families, all but one displaying parental consanguinity. Only two of these families were of European origin. We wished to determine the role of HPGD in causing PHO in non-consanguineous European families.

METHODS

Five previously unreported families of Caucasian European origin, with one or more individuals affected with typical PHO, were characterized clinically and by complete sequencing of the HPGD coding exons.

RESULTS

Biallelic HPGD mutations were identified in affected individuals in all the five families, confirming a very specific association of this phenotype with HPGD mutations. The previously described c.175_176delCT frameshift mutation was observed in association with two different alleles of an adjacent single nucleotide polymorphism.

CONCLUSIONS

Biallelic HPGD mutations are found in the majority of patients with typical PHO, and sequencing of the HPGD gene is a highly specific first-line investigation for patients presenting in this way, particularly during childhood. The c.175_176delCT frameshift mutation appears to be recurrent and to be the commonest HPGD mutation in Caucasian families.

HPGD mutations cause cranioosteoarthropathy but not autosomal dominant digital clubbing

Cranio-osteoarthropathy, clinically classified as a variant of primary hypertrophic osteoarthropathy, is a very rare autosomal-recessive condition characterized by delayed closure of the cranial sutures and fontanels, digital clubbing, arthropathy, and periostosis. Recently, mutations in the gene HPGD, which encodes the NAD(+)-dependent 15-hydroxyprostaglandin dehydrogenase, were reported in four families affected with primary hypertrophic osteoarthropathy and one family with autosomal-recessive isolated nail clubbing. We report the clinical and molecular findings in four patients from two families affected with cranio-osteoarthropathy and one family with isolated, autosomal dominant digital clubbing. Genome-wide homozygosity mapping identified a locus for cranio-osteoarthropathy harboring the HPGD gene in one affected family. We detected two novel homozygous mutations in HPGD in these families: a missense mutation affecting the NAD(+) binding motif and a frameshift mutation. The clinical presentation in our patients was variable. Digital clubbing and hyperhidrosis were present in all cases. Delayed closure of the cranial sutures and fontanels, periostosis, and arthropathy were not consistent clinical features. No HPGD mutation was detected in a familial case of autosomal dominant isolated digital clubbing. The failure to identify any mutation in a family with an autosomal dominant type of isolated digital clubbing suggests that HPGD is not the major gene for this condition.