Clinical, radiographic and molecular characterization of two unrelated families with multicentric osteolysis, nodulosis, and arthropathy.

BACKGROUND: Multicentric osteolysis nodulosis and arthropathy (MONA) is a rare autosomal recessive disorder characterized by marked progressive bone loss and joint destruction resulting in skeletal deformities. MONA is caused by MMP2 deficiency. Here we report clinical and molecular analyses of four patients in two families from Pakistan and Finland. METHODS: Clinical analyses including radiography were completed and blood samples were collected. The extracted DNA was subjected to whole-exome analysis or target gene sequencing. Segregation analyses were performed in the nuclear pedigree. Pathogenicity prediction scores for the selected variants and conservation analyses of affected amino acids were observed. RESULTS: The phenotype in the four affected individuals was consistent with multicentric osteolysis or MONA, as the patients had multiple affected joints, osteolysis of hands and feet, immobility of knee joint and progressive bone loss. Long-term follow up of the patients revealed the progression of the disease. We found a novel MMP2 c.1336 + 2T > G homozygous splice donor variant segregating with the phenotype in the Pakistani family while a MMP2 missense variant c.1188 C > A, p.(Ser396Arg) was homozygous in both Finnish patients. In-silico analysis predicted that the splicing variant may eventually introduce a premature stop codon in MMP2. Molecular modeling for the p.(Ser396Arg) variant suggested that the change may disturb MMP2 collagen-binding region. CONCLUSION: Our findings expand the genetic spectrum of Multicentric osteolysis nodulosis and arthropathy. We also suggest that the age of onset of this disorder may vary from childhood up to late adolescence and that a significant degree of intrafamilial variability may be present.

Novel form of rhizomelic skeletal dysplasia associated with a homozygous variant in GNPNAT1.

BACKGROUND: Studies exploring molecular mechanisms underlying congenital skeletal disorders have revealed novel regulators of skeletal homeostasis and shown protein glycosylation to play an important role. OBJECTIVE: To identify the genetic cause of rhizomelic skeletal dysplasia in a consanguineous Pakistani family. METHODS: Clinical investigations were carried out for four affected individuals in the recruited family. Whole genome sequencing (WGS) was completed using DNA from two affected and two unaffected individuals from the family. Sequencing data were processed, filtered and analysed. In silico analyses were performed to predict the effects of the candidate variant on the protein structure and function. Small interfering RNAs (siRNAs) were used to study the effect of Gnpnat1 gene knockdown in primary rat chondrocytes. RESULTS: The patients presented with short stature due to extreme shortening of the proximal segments of the limbs. Radiographs of one individual showed hip dysplasia and severe platyspondyly. WGS data analyses identified a homozygous missense variant c.226G>A; p.(Glu76Lys) in GNPNAT1, segregating with the disease. Glucosamine 6-phosphate N-acetyltransferase, encoded by the highly conserved gene GNPNAT1, is one of the enzymes required for synthesis of uridine diphosphate N-acetylglucosamine, which participates in protein glycosylation. Knockdown of Gnpnat1 by siRNAs decreased cellular proliferation and expression of chondrocyte differentiation markers collagen type 2 and alkaline phosphatase, indicating that Gnpnat1 is important for growth plate chondrocyte proliferation and differentiation. CONCLUSIONS: This study describes a novel severe skeletal dysplasia associated with a biallelic, variant in GNPNAT1. Our data suggest that GNPNAT1 is important for growth plate chondrogenesis.

A dual-acting DNASE1/DNASE1L3 biologic prevents autoimmunity and death in genetic and induced lupus models.

A defining feature of systemic lupus erythematosus (SLE) is loss of tolerance to self-DNA, and deficiency of DNASE1L3, the main enzyme responsible for chromatin degradation in blood, is also associated with SLE. This association can be found in an ultrarare population of pediatric patients with DNASE1L3 deficiency who develop SLE, adult patients with loss-of-function variants of DNASE1L3 who are at a higher risk for SLE, and patients with sporadic SLE who have neutralizing autoantibodies against DNASE1L3. To mitigate the pathogenic effects of inherited and acquired DNASE1L3 deficiencies, we engineered a long-acting enzyme biologic with dual DNASE1/DNASE1L3 activity that is resistant to DNASE1 and DNASE1L3 inhibitors. Notably, we found that the biologic prevented the development of lupus in Dnase1-/-Dnase1L3-/- double-knockout mice and rescued animals from death in pristane-induced lupus. Finally, we confirmed that the human isoform of the enzyme biologic was not recognized by autoantibodies in SLE and efficiently degraded genomic and mitochondrial cell-free DNA, as well as microparticle DNA, in SLE plasma. Our findings suggest that autoimmune diseases characterized by aberrant DNA accumulation, such as SLE, can be effectively treated with a replacement DNASE tailored to bypass pathogenic mechanisms, both genetic and acquired, that restrict DNASE1L3 activity.

Biallelic KIF24 Variants Are Responsible for a Spectrum of Skeletal Disorders Ranging From Lethal Skeletal Ciliopathy to Severe Acromesomelic Dysplasia.

Skeletal dysplasias comprise a large spectrum of mostly monogenic disorders affecting bone growth, patterning, and homeostasis, and ranging in severity from lethal to mild phenotypes. This study aimed to underpin the genetic cause of skeletal dysplasia in three unrelated families with variable skeletal manifestations. The six affected individuals from three families had severe short stature with extreme shortening of forelimbs, short long-bones, and metatarsals, and brachydactyly (family 1); mild short stature, platyspondyly, and metaphyseal irregularities (family 2); or a prenatally lethal skeletal dysplasia with kidney features suggestive of a ciliopathy (family 3). Genetic studies by whole genome, whole exome, and ciliome panel sequencing identified in all affected individuals biallelic missense variants in KIF24, which encodes a kinesin family member controlling ciliogenesis. In families 1 and 3, with the more severe phenotype, the affected subjects harbored homozygous variants (c.1457A>G; p.(Ile486Val) and c.1565A>G; p.(Asn522Ser), respectively) in the motor domain which plays a crucial role in KIF24 function. In family 2, compound heterozygous variants (c.1697C>T; p.(Ser566Phe)/c.1811C>T; p.(Thr604Met)) were found C-terminal to the motor domain, in agreement with a genotype-phenotype correlation. In vitro experiments performed on amnioblasts of one affected fetus from family 3 showed that primary cilia assembly was severely impaired, and that cytokinesis was also affected. In conclusion, our study describes novel forms of skeletal dysplasia associated with biallelic variants in KIF24. To our knowledge this is the first report implicating KIF24 variants as the cause of a skeletal dysplasia, thereby extending the genetic heterogeneity and the phenotypic spectrum of rare bone disorders and underscoring the wide range of monogenetic skeletal ciliopathies. © 2022 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

RIN2 and BBS7 variants as cause of a coincidental syndrome.

BBS7 and RIN2 variants cause Bardet Biedl syndrome and RIN2 syndrome respectively. We investigated a consanguineous family in which five individuals manifested different phenotypes. Whole-exome sequencing analyses of the individual with multiple phenotypes revealed homozygosity for novel pathogenic variants in his DNA sample; a frameshift variant in RIN2 (c.1938delT) and a splice-site variant in BBS7 (c.1677-1G > A). Other affected individuals were homozygous for a variant in only one of either gene and consequently manifested phenotypes respective to one disorder. Our work shows that exome sequencing of the most severely affected individual can help in the identification of pathogenic variants in more than one involved genes in a particular family.