Cartilage hair hypoplasia: characteristics and orthopaedic manifestations

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.

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".

Molecular etiology of defective nuclear and mitochondrial ribosome biogenesis: Clinical phenotypes and therapy

Ribosomopathies are rare congenital disorders associated with defective ribosome biogenesis due to pathogenic variations in genes that encode proteins related to ribosome function and biogenesis. Defects in ribosome biogenesis result in a nucleolar stress response involving the TP53 tumor suppressor protein and impaired protein synthesis leading to a deregulated translational output. Despite the accepted notion that ribosomes are omnipresent and essential for all cells, most ribosomopathies show tissue-specific phenotypes affecting blood cells, hair, spleen, or skin. On the other hand, defects in mitochondrial ribosome biogenesis are associated with a range of clinical manifestations affecting more than one organ. Intriguingly, the deregulated ribosomal function is also a feature in several human malignancies with a selective upregulation or downregulation of specific ribosome components. Here, we highlight the clinical conditions associated with defective ribosome biogenesis in the nucleus and mitochondria with a description of the affected genes and the implicated pathways, along with a note on the treatment strategies currently available for these disorders.

Structural abnormalities and osteopathic considerations in primary immunodeficiencies

Structural skeletal abnormalities are associated with primary immunodeficient (PID) patients. These abnormalities have not been well studied in PID with reference to osteopathic medicine tenets. Osteopathic structural examinations of PID patients with respect to these tenets and the diagnosis of somatic dysfunctions preventing the free flow of lymph fluids back into the circulation and the disruption of the skeletal microenvironment may have an impact on the status of the immune system in patients with a PID. A standardized evaluation was conducted in a patient with a phosphatidylinositol 3-kinase regulatory subunit 1 (PIK3R1) mutation who presented with skeletal abnormalities. A literature review was also conducted to determine the breadth of other PIDs with structural irregularities. Osteopathic structural clinical examinations (OSCEs) were performed by an osteopathic medical student, fellow, and attending after receiving informed consent from the patient. The findings were collected regionally noting severity, tissue texture changes, asymmetry, altered range of motion (ROM), and tenderness according to DO-Touch.NET physical examination and treatment form. A literature review was conducted utilizing various search engines and the textbook, Stiehm's Immune Deficiencies, 4th edition. The significant findings found from the patient were right sidebending rotation cranial strain pattern with decreased left temporal bone motion, temporomandibular joint crepitus, and right deviation upon mandibular opening. The thoracolumbar region revealed tissue tenderness and restricted psoas ROM. Bilateral sacroiliac joint tenderness, right superior sheering, and anterior innominate rotation, along with left-on-left sacral flexion, were associated with valgus knees. The literature search showed multiple other PIDs outside of PIK3R1 that have associated skeletal and structural abnormalities. Irregular skeletal features found in immunodeficient patients may have an additive defect on the immunological responses due to somatic dysfunction impinging on the lymphatic flow to the central circulation. Other different immunodeficient patients suffer from boney structural abnormalities, which may lead to further immune hindrance caused by impingement of flow as well as bone marrow microenvironment impact on the peripheral immunological output. We present the first osteopathic examination with detailed findings of somatic dysfunction in a patient with PID. Future studies on PID patients should require more attention to structure and function, as found by a thorough osteopathic examination in order to unrestrict preformed cellular and humoral components back into the peripheral circulation.

Uncovering pathways regulating chondrogenic differentiation of CHH fibroblasts

Mutations in the non-coding snoRNA component of mitochondrial RNA processing endoribonuclease (RMRP) are the cause of cartilage-hair hypoplasia (CHH). CHH is a rare form of metaphyseal chondrodysplasia characterized by disproportionate short stature and abnormal growth plate development. The process of chondrogenic differentiation within growth plates of long bones is vital for longitudinal bone growth. However, molecular mechanisms behind impaired skeletal development in CHH patients remain unclear. We employed a transdifferentiation model (FDC) combined with whole transcriptome analysis to investigate the chondrogenic transdifferentiation capacity of CHH fibroblasts and to examine pathway regulation in CHH cells during chondrogenic differentiation. We established that the FDC transdifferentiation model is a relevant in vitro model of chondrogenic differentiation, with an emphasis on the terminal differentiation phase, which is crucial for longitudinal bone growth. We demonstrated that CHH fibroblasts are capable of transdifferentiating into chondrocyte-like cells, and show a reduced commitment to terminal differentiation. We also found a number of key factors of BMP, FGF, and IGF-1 signalling axes to be significantly upregulated in CHH cells during the chondrogenic transdifferentiation. Our results support postulated conclusions that RMRP has pleiotropic functions and profoundly affects multiple aspects of cell fate and signalling. Our findings shed light on the consequences of pathological CHH mutations in snoRNA RMRP during chondrogenic differentiation and the relevance and roles of non-coding RNAs in genetic diseases in general.

Homozygous n.64C>T mutation in mitochondrial RNA-processing endoribonuclease gene causes cartilage hair hypoplasia syndrome in two siblings

Cartilage hair hypoplasia syndrome (OMIM # 250250) is a rare autosomal recessive metaphyseal dysplasia, characterized by disproportionate short stature, hair hypoplasia and variable extra-skeletal manifestations, including immunodeficiency, anemia, intestinal diseases and predisposition to cancers. Cartilage hair hypoplasia syndrome has a broad phenotype and it is caused by homozygous or compound heterozygous mutation in the mitochondrial RNA-processing endoribonuclease on chromosome 9p13. Although it is well known as a primordial dwarfism, descriptions of the prenatal growth are missing. To add further details to the knowledge of the phenotypic spectrum of the disease, we report on two siblings with cartilage hair hypoplasia syndrome, presenting n.64C > T homozygous mutation in the mitochondrial RNA-processing endoribonuclease gene. We describe the prenatal and postnatal growth pattern of the two affected patients, showing severe pre- and post-natal growth deficiency.

Rmrp Mutation Disrupts Chondrogenesis and Bone Ossification in Zebrafish Model of Cartilage-Hair Hypoplasia via Enhanced Wnt/β-Catenin Signaling

Cartilage-hair hypoplasia (CHH) is an autosomal recessive metaphyseal chondrodysplasia characterized by bone dysplasia and many other highly variable features. The gene responsible for CHH is the RNA component of the mitochondrial RNA-processing endoribonuclease (RMRP) gene. Currently, the pathogenesis of osteochondrodysplasia and extraskeletal manifestations in CHH patients remains incompletely understood; in addition, there are no viable animal models for CHH. We generated an rmrp KO zebrafish model to study the developmental mechanisms of CHH. We found that rmrp is required for the patterning and shaping of pharyngeal arches. Rmrp mutation inhibits the intramembranous ossification of skull bones and promotes vertebrae ossification. The abnormalities of endochondral bone ossification are variable, depending on the degree of dysregulated chondrogenesis. Moreover, rmrp mutation inhibits cell proliferation and promotes apoptosis through dysregulating the expressions of cell-cycle- and apoptosis-related genes. We also demonstrate that rmrp mutation upregulates canonical Wnt/β-catenin signaling; the pharmacological inhibition of Wnt/β-catenin could partially alleviate the chondrodysplasia and increased vertebrae mineralization in rmrp mutants. Our study, by establishing a novel zebrafish model for CHH, partially reveals the underlying mechanism of CHH, hence deepening our understanding of the role of rmrp in skeleton development.

[Syndromic Hirschsprung&prime;s disease and its mode of inheritance]

Hirschsprung&prime;s disease (HSCR) is one of the major causes of chronic incomplete intestinal obstruction in children. HSCR is considered a type of neurocristopathy caused by no colonization of ganglion cells on some parts of the bowel wall due to abnormal termination of the migration of vagal neural cells during embryonic development. This disease can be classified into different types according to the length of the affected intestinal canal. Most HSCR patients present with single deformity, but some HSCR patients are affected by other deformities, which constitutes syndromic HSCR, such as congenital central hypoventilation syndrome, Fryns syndrome, and cartilage-hair hypoplasia syndrome. Most syndromes have abnormal genetic material. An adequate knowledge of syndromic HSCR is of vital importance for accurate diagnosis and prognostic evaluation. This article reviews the clinical manifestations, genetic basis, and genetic modes of different types of syndromic HSCR.

Clinical and molecular diagnosis of a cartilage-hair hypoplasia with IGF-1 deficiency

Cartilage-hair hypoplasia syndrome (CHH) is a rare autosomal recessive condition characterized by metaphyseal chondrodysplasia and characteristic hair, together with a myriad of other symptoms, being most common immunodeficiency and gastrointestinal complications. A 15-year-old Mexican male initially diagnosed with Hirschsprung disease and posterior immunodeficiency, presents to our department for genetic and complementary evaluation for suspected CHH. Physical, biochemical, and genetic studies confirmed CHH together with IGF-1 deficiency. For this reason, we propose IGF-1 replacement therapy for its well-known actions on hematopoiesis, immune function and maturation, and metabolism. © 2016 Wiley Periodicals, Inc.