Defective in-vitro colony formation of haematopoietic progenitors in patients with cartilage-hair hypoplasia and history of anaemia

Anemia in patients with cartilage hair hypoplasia: a narrative review and recommendations

Cartilage hair hypoplasia (CHH) can lead to the development of anemia as a possible complication of this rare genetic disease. Despite various publications on anemia in CHH patients, a comprehensive review on this topic has not been conducted. This article reviews publications on anemia in CHH patients published from 1981 to 2022. Most authors have reported macrocytic anemia and blood transfusion as a common treatment approach in this patient group. Recommended guidelines for managing anemia in CHH patients include iron chelation therapy for those requiring multiple blood transfusions, regular assessment of anemia symptoms, red blood cell parameters, and immune system function. Future studies should evaluate the erythroid system in a larger cohort of CHH patients, considering key factors such as concurrent illnesses, age, height, and weight.

Sirolimus Restores Erythropoiesis and Controls Immune Dysregulation in a Child With Cartilage-Hair Hypoplasia: A Case Report

Cartilage-hair hypoplasia (CHH) is a syndromic immunodeficiency characterized by metaphyseal dysplasia, cancer predisposition, and varying degrees of anemia. It may present as severe combined immunodeficiency in infancy, or slowly progress until fully manifesting in late adolescence/adulthood. No targeted treatment is currently available, and patients are usually managed with supportive measures, or are offered a bone marrow transplant if the clinical phenotype is severe and a suitable donor is available. We report the case of a young girl presenting with transfusion-dependent erythropoietic failure and immunological features resembling autoimmune lymphoproliferative syndrome who responded well to empirical sirolimus. She later developed a marked growth delay, which was ultimately attributed to metaphyseal dysplasia. A diagnosis of CHH was reached through whole-genome sequencing (WGS), after a less sensitive genetic diagnostic strategy failed. The patient eventually underwent a haploidentical bone marrow transplant due to progressive combined immunodeficiency manifested as cryptococcal meningoencephalitis. This case illustrates the potential role of sirolimus in correcting anemia and partially controlling the immune aberrations associated with CHH, and serves as a reminder of the invaluable role of WGS in diagnosing patients with complex and atypical presentations.

Immunodeficiency in cartilage-hair hypoplasia: Pathogenesis, clinical course and management

Cartilage-hair hypoplasia (CHH) is an autosomal recessive syndromic immunodeficiency with skeletal dysplasia, short stature, hypotrichosis, variable degree of immune dysfunction and increased incidence of anaemia, Hirschsprung disease and malignancy. CHH is caused by variants in the RMRP gene, encoding the untranslated RNA molecule of the mitochondrial RNA-processing endoribonuclease, which participates in for example cell cycle regulation and telomere maintenance. Recent studies have expanded our understanding of the complex pathogenesis of CHH. Immune dysfunction has a major impact on clinical course and prognosis. Clinical features of immune dysfunction are highly variable, progressive and include infections, lung disease, immune dysregulation and malignancy. Mortality is increased compared with the general population, due to infections, malignancy and pulmonary disease. Several risk factors for early mortality have been reported in the Finnish CHH cohort and can be used to guide management. Newborn screening for severe combined immunodeficiency can possibly be of prognostic value in CHH. Regular follow-up by a multidisciplinary team should be implemented to address immune dysfunction in all patients with CHH, also in asymptomatic cases. Haematopoietic stem cell transplantation can cure immune dysfunction, but its benefits in mildly symptomatic patients with CHH remain debatable. Further research is needed to understand the mechanisms behind the variability of clinical features, to search for potential molecular treatment targets, to examine and validate risk factors for early mortality outside the Finnish CHH cohort and to develop management guidelines. This review focuses on the pathogenesis, clinical course and management of CHH.

The human long non-coding RNA gene RMRP has pleiotropic effects and regulates cell-cycle progression at G2

RMRP was the first non-coding nuclear RNA gene implicated in a disease. Its mutations cause cartilage-hair hypoplasia (CHH), an autosomal recessive skeletal dysplasia with growth failure, immunodeficiency, and a high risk for malignancies. This study aimed to gain further insight into the role of RNA Component of Mitochondrial RNA Processing Endoribonuclease (RMRP) in cellular physiology and disease pathogenesis. We combined transcriptome analysis with single-cell analysis using fibroblasts from CHH patients and healthy controls. To directly assess cell cycle progression, we followed CHH fibroblasts by pulse-labeling and time-lapse microscopy. Transcriptome analysis identified 35 significantly upregulated and 130 downregulated genes in CHH fibroblasts. The downregulated genes were significantly connected to the cell cycle. Multiple other pathways, involving regulation of apoptosis, bone and cartilage formation, and lymphocyte function, were also affected, as well as PI3K-Akt signaling. Cell-cycle studies indicated that the CHH cells were delayed specifically in the passage from G2 phase to mitosis. Our findings expand the mechanistic understanding of CHH, indicate possible pathways for therapeutic intervention and add to the limited understanding of the functions of RMRP.

The inherited bone marrow failure syndromes

Molecular pathogenesis may be elucidated for inherited bone marrow failure syndromes (IBMFS). The study and presentation of the details of their molecular biology and biochemistry is warranted for appropriate diagnosis and management of afflicted patients and to identify the physiology of the normal hematopoiesis and mechanisms of carcinogenesis. Several themes have emerged within each subsection of IBMFS, including the ribosomopathies, which include ribosome assembly and ribosomal RNA processing. The Fanconi anemia pathway has become interdigitated with the familial breast cancer syndromes. In this article, the diseases that account for most IBMFS diagnoses are analyzed.

Hypoplastic anemia in cartilage-hair hypoplasia-balancing between iron overload and chelation

OBJECTIVE

To evaluate the severity of iron overload and the success of iron chelation therapy in patients with cartilage-hair hypoplasia (CHH) and hypoplastic anemia, with particular focus on adverse effects of iron chelators.

STUDY DESIGN

Four of the 23 presently surviving Finnish patients with CHH under 18 years of age are dependent on regular red blood cell transfusions. Their hospital records were reviewed for history of anemia and chelation therapy. Cumulative iron load from transfusions was calculated. Efficacy of the chelation therapy was evaluated biochemically and by liver iron content assessments.

RESULTS

At the introduction of iron chelation, the patients had received on average 99 (37-151) transfusions; the mean cumulative iron overload was 4640 (800-8200) mg, the annual iron accumulation rate 0.35 (0.25-0.41) mg/kg/d, and the mean plasma ferritin was 2896 (1217-6240) μg/L. Liver iron content, determined by biopsy in 3 patients, was on average 20.0 (6.6-30.0) mg/g liver dry weight. All patients, except 1 with Hirschsprung disease, tolerated deferoxamine, deferiprone, and deferasirox therapy well, showing only mild adverse effects typical for the agents. Plasma ferritin levels and liver magnetic resonance imaging T2* of iron overload showed successful chelation.

CONCLUSION

Iron chelation is well tolerated in patients with CHH, with possible exception of patients with Hirschsprung disease. Successful chelation will prepare for hematopoietic stem cell transplantation in patients with CHH with persistent transfusion dependency.

The molecular basis of the cartilage-hair hypoplasia-anauxetic dysplasia spectrum

Cartilage-hair hypoplasia and anauxetic dysplasia are two autosomal recessive skeletal dysplasias characterized by different degrees from metaphyseal to spondylo-meta-epiphyseal dysplasia and variable additional features including predisposition to cancer, anemia, immunodeficiency, and gastrointestinal malabsorption and Hirschsprung's disease. Both are caused by mutations in the untranslated RMRP gene, which forms the RNA subunit of the RNase MRP complex. This complex is involved in the ribosome assembly by cleavage of 5.8S rRNA, cell cycle control by Cyclin B2 mRNA cleavage at the end of mitosis, processing the mitochondrial RNA, and forming a complex with hTERT suggesting a possible involvement in expression regulation by siRNA synthesis. The degree of skeletal dysplasia correlates mainly with the rRNA cleavage activity, whereas significantly diminished mRNA cleavage activity is a prerequisite for immunodeficiency. Thus, the clinical phenotype emerges in most cases of the combined effect on the respective effect on RNase MRP function.

[Cartilage-hair hypoplasia]

Cartilage-hair hypoplasia is a rare, autosomal recessive primary immunodeficiency disorder characterized by predominantly T-cell deficiency and metaphyseal chondrodysplasia. The authors summarize current knowledge on molecular genetics, diagnostic characteristics and therapeutic options of this inherited immunodeficiency.

Mechanisms of Disordered Granulopoiesis in Congenital Neutropenia

Neutrophils are critical components of the innate immune response, and persistent neutropenia is associated with a marked susceptibility to infection. There are a number of inherited clinical syndromes in which neutropenia is a prominent feature. A study of these rare disorders has provided insight into the mechanisms regulating normal neutrophil homeostasis. Tremendous progress has been made at defining the genetic basis of these disorders. Herein, progress in understanding the genetic basis and molecular mechanisms of these disorders is discussed. We have focused our discussion on inherited disorders in which neutropenia is the sole or major hematopoietic defect.

The natural history of severe anemia in cartilage-hair hypoplasia

Anemia is seen in over 80% of patients with cartilage-hair hypoplasia (CHH). While this is usually mild and self-limited, some patients demonstrate a severe, persistent anemia resembling that seen in Diamond-Blackfan anemia (DBA). This paper examines the natural history of 12 patients with CHH and severe anemia. Phenotypic features and mutation data (where available) were reviewed, but no significant differences were found that predicted severe anemia. Severe anemia is estimated to occur in approximately 6% of CHH patients and is permanent in more than half of these patients. Thrombocytosis, though not previously reported in CHH, was noted in five patients, similar to that seen in DBA. The role of possible gene-gene and gene-environment interactions is discussed.

Granulocyte colony-stimulating factor-responsive chronic neutropenia in cartilage-hair hypoplasia

: Chronic neutropenia is common in children with cartilage-hair hypoplasia (CHH). The authors describe a 6-year-old with severe CHH, moderate neutropenia associated with serum IgG antibodies directed against Fcgamma-RIIIb (NA1/2), and frequent bacterial infections. In this patient, long-term administration of granulocyte colony-stimulating factor increased peripheral neutrophil counts and prevented recurrent hospitalizations for bacterial lower respiratory tract infections.

The Saccharomyces cerevisiae RNase mitochondrial RNA processing is critical for cell cycle progression at the end of mitosis

We have identified a cell cycle delay in Saccharomyces cerevisiae RNase MRP mutants. Mutants delay with large budded cells, dumbbell-shaped nuclei, and extended spindles characteristic of "exit from mitosis" mutants. In accord with this, a RNase MRP mutation can be suppressed by overexpressing the polo-like kinase CDC5 or by deleting the B-type cyclin CLB1, without restoring the MRP-dependent rRNA-processing step. In addition, we identified a series of genetic interactions between RNase MRP mutations and mutations in CDC5, CDC14, CDC15, CLB2, and CLB5. As in most "exit from mitosis" mutants, levels of the Clb2 cyclin were increased. The buildup of Clb2 protein is not the result of a defect in the release of the Cdc14 phosphatase from the nucleolus, but rather the result of an increase in CLB2 mRNA levels. These results indicate a clear role of RNase MRP in cell cycle progression at the end of mitosis. Conservation of this function in humans may explain many of the pleiotropic phenotypes of cartilage hair hypoplasia.

Hirschsprung disease associated with severe cartilage-hair hypoplasia

Cartilage-hair hypoplasia is a chondrodysplasia with a high incidence of Hirschsprung disease. This study suggests that Hirschsprung disease is associated especially with severe cartilage-hair hypoplasia: the patients with Hirschsprung disease had severe growth failure and a higher incidence of alopecia, infections, malignancies, and childhood anemia than the patients with cartilage-hair hypoplasia who did not have Hirschsprung disease.

Impaired spermatogenesis: an unrecognized feature of cartilage-hair hypoplasia

BACKGROUND

Cartilage-hair hypoplasia (CHH), an autosomal recessive chondrodysplasia, is characterized by severe growth failure, hypoplastic hair, impaired immunity, and deficient erythropoiesis. These features may result from a generalized defect in cell proliferation.

AIM

In order to investigate whether an impairment of cell proliferation is present in spermatogenesis, we analysed fertility in a clinical and laboratory study of adult males with CHH.

METHODS

Eleven adult males (median age 29 years, range 21-49 years) with CHH were included in the study. The patients were examined clinically for testicular volume and other clinical characteristics. Blood samples were collected to determine serum concentrations of sex hormones, sex hormone-binding globulin, inhibin B and gonadotrophins (basal and gonadotrophin-releasing hormone-stimulated). Semen samples were analysed for volume, sperm concentration, motility, morphology, and antibody status.

RESULTS

The testicular size was subnormal in some patients, but the serum concentrations of testosterone, inhibin B and gonadotrophins were usually normal. The semen analyses were not within normal limits in any of the patients, as indicated by low sperm concentration, decreased motility and/or morphological changes.

CONCLUSIONS

The defect in cell proliferation in men with CHH also involves the spermatogenic cells and is evident as an impairment of spermatogenesis.