RNase Mitochondrial RNA Processing Research Articles

RMRP-related short stature: A report of six additional Japanese individuals with cartilage hair hypoplasia and literature review.

Biallelic pathogenic variants in RMRP, the gene encoding the RNA component of RNase mitochondrial RNA processing enzyme complex, have been reported in individuals with cartilage hair hypoplasia (CHH). CHH is prevalent in Finnish and Amish populations due to a founder pathogenic variant, n.71A > G. Based on the manifestations in the Finnish and Amish individuals, the hallmarks of CHH are prenatal-onset growth failure, metaphyseal dysplasia, hair hypoplasia, immunodeficiency, and other extraskeletal manifestations. Herein, we report six Japanese individuals with CHH from four families. All probands presented with moderate short stature with mild metaphyseal dysplasia or brachydactyly. One of them had hair hypoplasia and the other immunodeficiency. By contrast, the affected siblings of two families showed only mild short stature. We also reviewed all previously reported 13 Japanese individuals. No n.71A > G allele was detected. The proportions of Japanese versus Finnish individuals were 0% versus 70% for birth length < -2.0 SD, 84% versus 100% for metaphyseal dysplasia and 26% versus 88% for hair hypoplasia. Milder manifestations in the Japanese individuals may be related to the difference of genotypes. The mildest form of CHH phenotypes is mild short stature without overt skeletal alteration or extraskeletal manifestation and can be termed "RMRP-related short stature".

A Novel Method to Isolate RNase MRP Using RNA Streptavidin Aptamer Tags.

Interactions between RNA-binding proteins and RNA molecules are at the center of multiple biological processes. Therefore, accurate characterization of the composition of ribonucleoprotein complexes (RNPs) is crucial. Ribonuclease (RNase) for mitochondrial RNA processing (MRP) and RNase P are highly similar RNPs that play distinct roles at the cellular level; as a consequence, the specific isolation of either of these complexes is essential to study their biochemical function. Since their protein components are nearly identical, purification of these endoribonucleases using protein-centric methods is not feasible. Here, we describe a procedure employing an optimized high-affinity streptavidin-binding RNA aptamer, termed S1m, to purify RNase MRP free of RNase P. This report details all steps from the RNA tagging to the characterization of the purified material. We show that using the S1m tag allows efficient isolation of active RNase MRP.

M170 SHORT STATURE AND RECURRENT INFECTIONS: A CASE OF CARTILAGE-HAIR HYPOPLASIA FROM COMPOUND HETEROZYGOUS RMRP MUTATIONS

Cartilage-hair hypoplasia (CHH) is an autosomal recessive disorder characterized by metaphyseal chondrodysplasia, dwarfism, hypotrichosis, and immunodeficiency. We present a case of CHH diagnosed later in childhood and subsequently found to have two deleterious compound heterozygous mutations of the ribonuclease mitochondrial RNA-processing (RMRP) gene.

Long Noncoding RNA RMRP Suppresses the Tumorigenesis of Hepatocellular Carcinoma Through Targeting microRNA-766.

PurposeThis study aimed to explore the regulatory effect of long noncoding RNA (lncRNA) ribonuclease mitochondrial RNA processing gene (RMRP) on hepatocellular carcinoma (HCC).MethodsThe expression of RMRP in HCC tissues and cell lines was assessed by qRT-PCR. Kaplan–Meier method was utilized to analyze the correlation between RMRP expression and the survival of HCC patients. MHCC97H and HuH7 cells were transfected with pcDNA3.1-RMRP or pcDNA3.1, respectively. MTT and flow cytometry assays were conducted to examine the proliferation and apoptosis of HCC cells, respectively. The migration and invasion of HCC cells were assessed using wound healing and transwell assays, respectively. StarBase3.0 and dual-luciferase reporter gene assay were used to identify the target relationship between miR-766 and RMRP. A xenografted tumor model was established in rats to evaluate the effect of RMRP in vivo.ResultsRMRP was down-regulated in HCC tissues and cells. Low expression of RMRP was correlated with poor survival of HCC patients. The A495 value and colony number were significantly decreased in pcDNA3.1-RMRP-transfected MHCC97H and HuH7 cells. The apoptosis rate was significantly increased in pcDNA3.1-RMRP-transfected MHCC97H and HuH7 cells. The migration rate and the number of invasive cells were significantly decreased in pcDNA3.1-RMRP-transfected MHCC97H and HuH7 cells. MiR-766 was a target of RMRP and eliminated the anti-tumor effect of RMRP on MHCC97H cells. The up-regulation of RMRP suppressed the growth of xenograft tumors in rats.ConclusionOverexpression of RMRP suppressed the tumorigenesis of HCC by targeting miR-766.

M241 NOVEL RMRP VARIANT PRESENTING WITH DECREASED TELOMERE LENGTH AND BONE MARROW FAILURE

Cartilage-hair hypoplasia (CHH) is an autosomal recessive metaphyseal chondrodysplasia caused by a variant in the ribonuclease mitochondrial RNA-processing (RMRP) gene that manifests with hypoplastic hair, dwarfism, various impairments in cellular immunity, and a propensity towards malignancy.

The antiviral protein viperin regulates chondrogenic differentiation via CXCL10 protein secretion

Viperin (also known as radical SAM domain–containing 2 (RSAD2)) is an interferon-inducible and evolutionary conserved protein that participates in the cell's innate immune response against a number of viruses. Viperin mRNA is a substrate for endoribonucleolytic cleavage by RNase mitochondrial RNA processing (MRP) and mutations in the RNase MRP small nucleolar RNA (snoRNA) subunit of the RNase MRP complex cause cartilage-hair hypoplasia (CHH), a human developmental condition characterized by metaphyseal chondrodysplasia and severe dwarfism. It is unknown how CHH-pathogenic mutations in RNase MRP snoRNA interfere with skeletal development, and aberrant processing of RNase MRP substrate RNAs is thought to be involved. We hypothesized that viperin plays a role in chondrogenic differentiation. Using immunohistochemistry, real-time quantitative PCR, immunoblotting, ELISA, siRNA-mediated gene silencing, plasmid-mediated gene overexpression, label-free MS proteomics, and promoter reporter bioluminescence assays, we discovered here that viperin is expressed in differentiating chondrocytic cells and regulates their protein secretion and the outcome of chondrogenic differentiation by influencing transforming growth factor β (TGF-β)/SMAD family 2/3 (SMAD2/3) activity via C-X-C motif chemokine ligand 10 (CXCL10). Of note, we observed disturbances in this viperin–CXCL10–TGF-β/SMAD2/3 axis in CHH chondrocytic cells. Our results indicate that the antiviral protein viperin controls chondrogenic differentiation by influencing secretion of soluble proteins and identify a molecular route that may explain impaired chondrogenic differentiation of cells from individuals with CHH.

NEWBORN SCREEN AND CHALLENGES IN DIAGNOSIS OF LEAKY SCID AND CARTILAGE HAIR HYPOPLASIA

Introduction Cartilage-hair hypoplasia (CHH) is a rare disorder of skeletal dysplasia with varying degrees of immunodeficiency. Diagnosis is clinical with affected individuals displaying disproportionately short limbs and fine sparse hair. Genetic analysis of the ribonuclease mitochondrial RNA processing gene (RMRP) is confirmatory. Case Description The patient is an ex-38-week male born to non-consanguineous parents of Mexican descent who is status post colostomy after failing to pass meconium due to Hirshprung Disease (HD). Newborn screen revealed TRECs of 1 and flow cytometry showed 446 CD3 cells with proportionally low naïve subset (180) and low recent thymic emigrants (110). Mitogen and CD3 stimulated lymphoproliferation were low normal. His SCID gene panel revealed a compound heterozygous mutation in the RMRP gene. Skeletal survey was unremarkable and he was non-dysmorphic. He was ultimately discharged home with climbing CD3 populations. At 6 months of age his CD3 count was 970 and he had protective vaccine titers to haemophilus influenza and tetanus after two doses of vaccines. Discussion This case represents a unique presentation of CHH given lack of skeletal dysplasia and classic hair findings. The diagnosis was not made clinically but rather by laboratory studies: initially with the results of the failed newborn screen and later by focused genetic testing. Importantly, this ribosomal defect is not found on whole exome sequencing. Unlike our patient, prior reports of CHH with HD describe severe immunodeficiency. In this case, reassessment and clinical vigilance are essential before moving forward with hematopoietic stem cell transplant. Cartilage-hair hypoplasia (CHH) is a rare disorder of skeletal dysplasia with varying degrees of immunodeficiency. Diagnosis is clinical with affected individuals displaying disproportionately short limbs and fine sparse hair. Genetic analysis of the ribonuclease mitochondrial RNA processing gene (RMRP) is confirmatory. The patient is an ex-38-week male born to non-consanguineous parents of Mexican descent who is status post colostomy after failing to pass meconium due to Hirshprung Disease (HD). Newborn screen revealed TRECs of 1 and flow cytometry showed 446 CD3 cells with proportionally low naïve subset (180) and low recent thymic emigrants (110). Mitogen and CD3 stimulated lymphoproliferation were low normal. His SCID gene panel revealed a compound heterozygous mutation in the RMRP gene. Skeletal survey was unremarkable and he was non-dysmorphic. He was ultimately discharged home with climbing CD3 populations. At 6 months of age his CD3 count was 970 and he had protective vaccine titers to haemophilus influenza and tetanus after two doses of vaccines. This case represents a unique presentation of CHH given lack of skeletal dysplasia and classic hair findings. The diagnosis was not made clinically but rather by laboratory studies: initially with the results of the failed newborn screen and later by focused genetic testing. Importantly, this ribosomal defect is not found on whole exome sequencing. Unlike our patient, prior reports of CHH with HD describe severe immunodeficiency. In this case, reassessment and clinical vigilance are essential before moving forward with hematopoietic stem cell transplant.

Cartilage hair hypoplasia: Heterogeneity in clinical features and management among siblings

Background: Cartilage-hair hypoplasia (CHH), caused by mutations in the ribonuclease mitochondrial RNA-processing (RMRP) gene, is associated with diverse immune abnormalities including combined immune deficiency (CID). Most patients with CHH are managed with supportive measurements, while few have received allogeneic hematopoietic stem cell transplantations (HSCT). The progression of the immune abnormalities and the impact of HSCT in patients with CHH and CID have not been well characterized. Methods: The clinical and laboratory findings of 2 siblings diagnosed in infancy with CHH and CID due to the common 70A>G mutation in RMRP, including the effects of HSCT performed in 1 of them, were compared. Results: Both patients suffered from recurrent respiratory infections at early age with reduced T cells numbers and responses. Patient 1 immune function continued to deteriorate leading to HSCT from an HLA-matched sibling at 4.5 years of age. The patient suffered acute and chronic graft versus host disease of the skin with residual mild joint contractures and scleroderma-like skin changes. Seven years after HSCT patient 1 has normal immune function. Immune evaluations of patient 2 in the first years of life indicated mild improvement. The patient did not have a suitable related HSCT donor and the family elected to continue with supportive care. At 7 years of age, patient 2 is clinically well and thriving with persistent T cell abnormalities. Conclusions: Close monitoring of immune function in early life for patients with CHH and CID as well as the availability of suitable donors assists in determining management, including HSCT. Statement of novelty: The manuscript demonstrates the importance of close monitoring and personalized approach in the management of patients affected by CHH.

Broadening the phenotypic spectrum of POP1‐skeletal dysplasias: identification of POP1 mutations in a mild and severe skeletal dysplasia

Processing of Precursor 1 (POP1) is a large protein common to the ribonuclease-mitochondrial RNA processing (RNase-MRP) and RNase-P (RMRP) endoribonucleoprotein complexes. Although its precise function is unknown, it appears to participate in the assembly or stability of both complexes. Numerous RMRP mutations have been reported in individuals with cartilage-hair hypoplasia (CHH) but, to date, only three POP1 mutations have been described in two families with features similar to anauxetic dysplasia (AD). We present two further individuals, one with severe short stature and a relatively mild skeletal dysplasia and another in whom AD was suspected. Biallelic POP1 mutations were identified in both. A missense mutation and a novel single base deletion were detected in proband 1, p.[Pro582Ser]:[Glu870fs*5]. Markedly reduced abundance of RMRP and elevated levels of pre5.8s rRNA was observed. In proband 2, a homozygous novel POP1 mutation was identified, p.[(Asp511Tyr)];[(Asp511Tyr)]. These two individuals show the phenotypic extremes in the clinical presentation of POP1-dysplasias. Although CHH and other skeletal dysplasias caused by mutations in RMRP or POP1 are commonly cited as ribosomal biogenesis disorders, recent studies question this assumption. We discuss the past and present knowledge about the function of the RMRP complex in skeletal development.

RNase MRP cleaves pre-tRNASer-Met in the tRNA maturation pathway.

Ribonuclease mitochondrial RNA processing (RNase MRP) is a multifunctional ribonucleoprotein (RNP) complex that is involved in the maturation of various types of RNA including ribosomal RNA. RNase MRP consists of a potential catalytic RNA and several protein components, all of which are required for cell viability. We show here that the temperature-sensitive mutant of rmp1, the gene for a unique protein component of RNase MRP, accumulates the dimeric tRNA precursor, pre-tRNASer-Met. To examine whether RNase MRP mediates tRNA maturation, we purified the RNase MRP holoenzyme from the fission yeast Schizosaccharomyces pombe and found that the enzyme directly and selectively cleaves pre-tRNASer-Met, suggesting that RNase MRP participates in the maturation of specific tRNA in vivo. In addition, mass spectrometry–based ribonucleoproteomic analysis demonstrated that this RNase MRP consists of one RNA molecule and 11 protein components, including a previously unknown component Rpl701. Notably, limited nucleolysis of RNase MRP generated an active catalytic core consisting of partial mrp1 RNA fragments, which constitute “Domain 1” in the secondary structure of RNase MRP, and 8 proteins. Thus, the present study provides new insight into the structure and function of RNase MRP.

Phenotypic Variations of Cartilage Hair Hypoplasia: Granulomatous Skin Inflammation and Severe T Cell Immunodeficiency as Initial Clinical Presentation in Otherwise Well Child with Short Stature

We report a child with short stature since birth who was otherwise well, presenting at 2.8 years with progressive granulomatous skin lesions when diagnosed with severe T cell immunodeficiency. When previously investigated for short stature, and at the time of current investigations, she had no radiological skeletal features characteristics for cartilage hair hypoplasia, but we found a disease causing RMRP (RNase mitochondrial RNA processing endoribonuclease) gene mutation. Whilst search for HLA matched unrelated donor for haematopoietic stem cell transplantation (HSCT) was underway, she developed rapidly progressive EBV-related lymphoproliferative disorder requiring laparotomy and small bowel resection, and was treated with anti-B cell monoclonal antibody and eventually curative allogeneic HSCT. Screening for RMRP gene mutations should be part of immunological evaluation of patients with ‘severe and/or combined’ T cell immunodeficiency of unknown origin, especially when associated with short stature and regardless of presence or absence of radiological skeletal features.

Foetal presentation of cartilage hair hypoplasia with extensive granulomatous inflammation

Cartilage-hair-hypoplasia is a rare autosomal recessive metaphyseal dysplasia due to RMRP (the RNA component of the RNase MRP ribonuclease mitochondrial RNA processing complex) gene mutations. So far, about 100 mutations have been reported in the promoter and the transcribed regions. Clinical characteristics include short-limbed short stature, sparse hair and defective cell-mediated immunity. We report herein the antenatal presentation of a female foetus, in whom CHH was suspected from 23 weeks' gestation, leading to a medical termination of the pregnancy at 34 weeks gestation, and thereafter confirmed by morphological and molecular studies. Post-mortem examination confirmed short stature and limbs, and revealed thymic hypoplasia associated with severe CD4 T-cell immunodeficiency along with extensive non caseating epithelioid granulomas in almost all organs, which to our knowledge has been described only in five cases. Molecular studies evidenced on one allele the most frequently reported founder mutation NR_003051: g.70A>G, which is present in 92% of Finnish patients with Cartilage Hair Hypoplasia. On the second allele, a novel mutation consisting of a 10 nucleotide insertion at position −18 of the promoter region of the RMRP gene (M29916.1:g.726_727insCTCACTACTC) was detected. The founder mutation was inherited from the father, and the novel mutation from the mother. To our knowledge, this case report represents the first detailed foetal analysis described in the literature.

Global Identification of New Substrates for the Yeast Endoribonuclease, RNase Mitochondrial RNA Processing (MRP)

RNase mitochondrial RNA processing (MRP) is an essential, evolutionarily conserved endoribonuclease composed of 10 different protein subunits and a single RNA. RNase MRP has established roles in multiple pathways including ribosome biogenesis, cell cycle regulation, and mitochondrial DNA replication. Although each of these functions is important to cell growth, additional functions may exist given the essential nature of the complex. To identify novel RNase MRP substrates, we utilized RNA immunoprecipitation and microarray chip analysis to identify RNA that physically associates with RNase MRP. We identified several new potential substrates for RNase MRP including a cell cycle-regulated transcript, CTS1; the yeast homolog of the mammalian p27(Kip1), SIC1; and the U2 RNA component of the spliceosome. In addition, we found RNase MRP to be involved in the regulation of the Ty1 transposon RNA. These results reinforce and broaden the role of RNase MRP in cell cycle regulation and help to identify new roles of this endoribonuclease.

GAMETOPHYTE DEFECTIVE 1, a Putative Subunit of RNases P/MRP, Is Essential for Female Gametogenesis and Male Competence in Arabidopsis

RNA biogenesis, including biosynthesis and maturation of rRNA, tRNA and mRNA, is a fundamental process that is critical for cell growth, division and differentiation. Previous studies showed that mutations in components involved in RNA biogenesis resulted in abnormalities in gametophyte and leaf development in Arabidopsis. In eukaryotes, RNases P/MRP (RNase mitochondrial RNA processing) are important ribonucleases that are responsible for processing of tRNA, and transcription of small non-coding RNAs. Here we report that Gametophyte Defective 1 (GAF1), a gene encoding a predicted protein subunit of RNases P/MRP, AtRPP30, plays a role in female gametophyte development and male competence. Embryo sacs were arrested at stages ranging from FG1 to FG7 in gaf1 mutant, suggesting that the progression of the gametophytic division during female gametogenesis was impaired in gaf1 mutant. In contrast, pollen development was not affected in gaf1. However, the fitness of the mutant pollen tube was weaker than that of the wild-type, leading to reduced transmission through the male gametes. GAF1 is featured as a typical RPP30 domain protein and interacts physically with AtPOP5, a homologue of RNases P/MRP subunit POP5 of yeast. Together, our data suggest that components of the RNases P/MRP family, such as RPP30, play important roles in gametophyte development and function in plants.

Whole-Exome Re-Sequencing in a Family Quartet Identifies POP1 Mutations As the Cause of a Novel Skeletal Dysplasia

Recent advances in DNA sequencing have enabled mapping of genes for monogenic traits in families with small pedigrees and even in unrelated cases. We report the identification of disease-causing mutations in a rare, severe, skeletal dysplasia, studying a family of two healthy unrelated parents and two affected children using whole-exome sequencing. The two affected daughters have clinical and radiographic features suggestive of anauxetic dysplasia (OMIM 607095), a rare form of dwarfism caused by mutations of RMRP. However, mutations of RMRP were excluded in this family by direct sequencing. Our studies identified two novel compound heterozygous loss-of-function mutations in POP1, which encodes a core component of the RNase mitochondrial RNA processing (RNase MRP) complex that directly interacts with the RMRP RNA domains that are affected in anauxetic dysplasia. We demonstrate that these mutations impair the integrity and activity of this complex and that they impair cell proliferation, providing likely molecular and cellular mechanisms by which POP1 mutations cause this severe skeletal dysplasia.

Functional characterization of theDrosophila MRP(mitochondrial RNA processing) RNA gene

MRP RNA is a noncoding RNA component of RNase mitochondrial RNA processing (MRP), a multi-protein eukaryotic endoribonuclease reported to function in multiple cellular processes, including ribosomal RNA processing, mitochondrial DNA replication, and cell cycle regulation. A recent study predicted a potential Drosophila ortholog of MRP RNA (CR33682) by computer-based genome analysis. We have confirmed the expression of this gene and characterized the phenotype associated with this locus. Flies with mutations that specifically affect MRP RNA show defects in growth and development that begin in the early larval period and end in larval death during the second instar stage. We present several lines of evidence demonstrating a role for Drosophila MRP RNA in rRNA processing. The nuclear fraction of Drosophila MRP RNA localizes to the nucleolus. Further, a mutant strain shows defects in rRNA processing that include a defect in 5.8S rRNA processing, typical of MRP RNA mutants in other species, as well as defects in early stages of rRNA processing.

Fatal adult-onset antibody deficiency syndrome in a patient with cartilage hair hypoplasia

Cartilage hair hypoplasia (CHH) is an autosomal recessive disorder caused by mutations in the ribonuclease mitochondrial RNA-processing (RMRP) gene. Although its most constant feature is metaphyseal dysplasia with short stature, CHH is associated with extraskeletal defects such as thin hair, anemia, immunodeficiency, and increased incidence of lymphomas. The spectrum of immunologic phenotypes in CHH translates into clinical severity. Whereas T-cell deficiency may remain subclinical or may result in severe combined immunodeficiency or Omenn syndrome, humoral immunodeficiency has only rarely been noted in these patients. Here we report the diagnosis of CHH in a woman who presented with severe short stature and a full-blown antibody deficiency, clinically resembling common variable immunodeficiency. Sequencing of the RMRP gene revealed compound heterozygosity for two novel mutations (g.68_69delinsTT and g.76C>T). Despite the late onset of immunodeficiency in the patient, its clinical course was severe, and the patient died 3 years after the first diagnosis.

Cartilage-hair hypoplasia: molecular basis and heterogeneity of the immunological phenotype

To report on the expanding clinical and immunological spectrum associated with ribonuclease mitochondrial RNA-processing mutations and to review the cellular and molecular mechanisms involved in the pathophysiology of cartilage-hair hypoplasia (CHH) and related disorders in humans. Different types of mutations are associated with skeletal or extraskeletal manifestations of CHH, respectively. In particular, severe immunodeficiency is mostly associated with mutations that alter cyclin B2 mRNA cleavage and thus are likely to reflect disturbances in cell cycle control. The first cases of ribonuclease mitochondrial RNA-processing mutations with severe immunodeficiency, but no skeletal abnormalities, have been identified. Abnormalities of ribosome biogenesis have been shown to cause distinct bone marrow failure syndromes, including CHH. However, the specific role of ribosomal and extraribosomal defects in the pathophysiology of the various phenotypic features of CHH remains undefined. Development of suitable animal models is needed to address this important issue.

Variability of clinical and laboratory features among patients with ribonuclease mitochondrial RNA processing endoribonuclease gene mutations

Cartilage hair hypoplasia is an autosomal recessive type of metaphyseal chondrodysplasia, caused by mutations in the ribonuclease mitochondrial RNA processing (RMRP) gene. Typical features of cartilage hair hypoplasia include short stature, a predisposition to malignancy, and a variable degree of impairment of cellular immunity. We sought to describe the heterogeneity of clinical and immunologic phenotype in 12 consecutive patients with RMRP mutations who were referred to 2 different institutions for immunologic evaluation. We have retrospectively analyzed the clinical and laboratory features in 12 patients with molecular defects in the RMRP gene. T-cell repertoire was investigated by quantitating Vbeta families' expression and analyzing their diversity. T-cell receptor excision circle analysis was used to study thymic output. All 12 patients had significant immune abnormalities, leading to severe immune deficiency in 9. CD8 lymphocytopenia was identified as a novel phenotype associated with RMRP mutations. Significant, even intrafamilial, phenotypic heterogeneity was observed. In 3 cases, severe immunodeficiency was the only phenotypic manifestation associated with RMRP mutations, a novel finding. Mutations leading to significant immune defects were most often located in the promoter, and the first case of a compound heterozygote for 2 such mutations is reported. This report broadens the spectrum of phenotypes associated with RMRP mutations and suggests that mutations in this gene should be considered when evaluating patients with combined immune deficiency, regardless of the presence of other manifestations.

Extended follow‐up of the Finnish cartilage‐hair hypoplasia cohort confirms high incidence of non‐Hodgkin lymphoma and basal cell carcinoma

Cartilage-hair hypoplasia (CHH) is an autosomal recessive chondrodysplasia with short stature, sparse hair and defective cell-mediated immunity. It is caused by mutations in the RMRP (ribonuclease mitochondrial RNA processing) gene, encoding the RNA component of the ribonuclease complex RNase MRP. The aim of this study was to further elucidate the risk and spectrum of cancer in CHH. A cohort of 123 Finnish patients with CHH (51 males) was followed for malignancy through the Finnish Cancer Registry. The number of identified cancers was compared with expected numbers of cancer using population-based data to obtain standardized incidence ratios (SIR). Hospital records were reviewed for clinical data related to the malignancies. During the follow-up (2,365 person-years; mean 19.2 years), 14 cases of cancer were diagnosed in the CHH cohort (expected number 2.0; SIR 7.0, CI 3.8-12). Non-Hodgkin lymphoma was the most frequent cancer type (n = 9; SIR 90.2, CI 39.0-180) followed by squamous cell carcinoma (3), leukemia (1) and Hodgkin lymphoma (1). One tumor was not histologically classified. Nine of the 14 cancers were diagnosed in patients less than 45 years of age. In addition, ten patients had basal cell carcinoma of the skin (expected number 0.3; SIR 33.2, CI 16-61). Patients with CHH have significantly increased risk for developing non-Hodgkin lymphoma or basal cell carcinoma at early age; the overall prognosis is poor. The underlying pathogenetic mechanisms remain to be elucidated in future studies. Careful follow-up, extending beyond pediatric age, is warranted for early diagnosis of malignancies.