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Newly cost-effective next-generation sequencing has led to an explosion of discoveries of novel genetic mutations that reveal the rampant “promiscuity” of genotype–phenotype relationships. Such discoveries should ultimately revolutionize clinical care. Ever since Mendel observed the varied phenotypes of peas — green or yellow, smooth or wrinkled — phenotypes have been used to systematically identify the genetic causes of disease. Similarly, genotype–phenotype relationships in humans could be dissected only if there were clearly recognizable, and relatively homogeneous, phenotypes. Since broad searches of genetic information were not technically feasible or cost-effective before the advent of next-generation sequencing (NGS), scientists studied well-characterized families to narrow the list of plausible genetic causes. However, being restricted to this set of “solvable” genetic problems led to ascertainment biases that favored highly penetrant mutations with straightforward functional . . .

Osteocytes are the terminally differentiated cell type of the osteoblastic lineage and have important functions in skeletal homeostasis. Although the transcriptional regulation of osteoblast differentiation has been well characterized, the factors that regulate differentiation of osteocytes from mature osteoblasts are poorly understood. Here we show that miR-23a∼27a∼24-2 (miR-23a cluster) promotes osteocyte differentiation. Osteoblast-specific miR-23a cluster gain-of-function mice have low bone mass associated with decreased osteoblast but increased osteocyte numbers. By contrast, loss-of-function transgenic mice overexpressing microRNA decoys for either miR-23a or miR-27a, but not miR24-2, show decreased osteocyte numbers. Moreover, RNA-sequencing analysis shows altered transforming growth factor-β (TGF-β) signalling. Prdm16 , a negative regulator of the TGF-β pathway, is directly repressed by miR-27a with concomitant alteration of sclerostin expression, and pharmacological inhibition of TGF-β rescues the phenotypes observed in the gain-of-function transgenic mice. Taken together, the miR-23a cluster regulates osteocyte differentiation by modulating the TGF-β signalling pathway through targeting of Prdm16 . Control of osteocyte differentiation is not well understood. Here the authors show that the miR-23 cluster represses the TGF-β signalling repressor Prdm16 in osteoblasts, thus enhancing osteocyte differentiation and a low bone mass phenotype.

This report identifies human skeletal diseases associated with mutations in WNT1 in a family with dominantly inherited early-onset osteoporosis and in another family with recessive osteogenesis imperfecta. WNT1 is shown to be an important ligand for regulating bone mass. Osteoporosis is a common skeletal disorder characterized by low bone mineral density (BMD), impaired bone quality, and fragility fractures. 1 Although multiple genetic loci, including those for WNT ligands, have been defined on the basis of genomewide association studies in patients with osteoporosis, the known loci are generally associated with odds ratios for fracture that are below 1.1. 2 Recently, novel metabolic pathways in bone cells have been discovered in patients with osteogenesis imperfecta, a mendelian disease characterized by brittle bones. 3 The role of the WNT pathway in bone formation and maintenance has been extensively studied since the identification of mutations in . . .

Kerstin Kutsche, Marco Tartaglia and colleagues show that missense mutations in KCNH1 and ATP6V1B2 cause Zimmermann-Laband syndrome, a disorder characterized by facial dysmorphism, intellectual disability, digit anomalies and hypertrichosis. Functional studies indicate that the KCNH1 mutations lead to altered channel activity. Zimmermann-Laband syndrome (ZLS) is a developmental disorder characterized by facial dysmorphism with gingival enlargement, intellectual disability, hypoplasia or aplasia of nails and terminal phalanges, and hypertrichosis 1 , 2 , 3 , 4 . We report that heterozygous missense mutations in KCNH1 account for a considerable proportion of ZLS. KCNH1 encodes the voltage-gated K + channel Eag1 (K v 10.1). Patch-clamp recordings showed strong negative shifts in voltage-dependent activation for all but one KCNH1 channel mutant (Gly469Arg). Coexpression of Gly469Arg with wild-type KCNH1 resulted in heterotetrameric channels with reduced conductance at positive potentials but pronounced conductance at negative potentials. These data support a gain-of-function effect for all ZLS-associated KCNH1 mutants. We also identified a recurrent de novo missense change in ATP6V1B2 , encoding the B2 subunit of the multimeric vacuolar H + ATPase, in two individuals with ZLS. Structural analysis predicts a perturbing effect of the mutation on complex assembly. Our findings demonstrate that KCNH1 mutations cause ZLS and document genetic heterogeneity for this disorder.

Six genes confer a high risk for developing breast cancer ( BRCA1/2 , TP53 , PTEN , STK11 , CDH1 ). Both BRCA1 and BRCA2 have DNA repair functions, and BRCA1/2 deficient tumors are now being targeted by poly(ADP-ribose) polymerase inhibitors. Other genes conferring an increased risk for breast cancer include ATM , CHEK2 , PALB2, BRIP1 and genome-wide association studies have identified lower penetrance alleles including FGFR2 , a minor allele of which is associated with breast cancer. We review recent findings related to the function of some of these genes, and discuss how they can be targeted by various drugs. Gaining deeper insights in breast cancer susceptibility will improve our ability to identify those families at increased risk and permit the development of new and more specific therapeutic approaches.

Sifrim–Hitz–Weiss syndrome (SIHIWES) is a recently described multisystemic neurodevelopmental disorder caused by de novo variants inCHD4. In this study, we investigated the clinical spectrum of the disorder, genotype–phenotype correlations, and the effect of different missense variants on CHD4 function. We collected clinical and molecular data from 32 individuals with mostly de novo variants in CHD4, identified through next-generation sequencing. We performed adenosine triphosphate (ATP) hydrolysis and nucleosome remodeling assays on variants from five different CHD4 domains. The majority of participants had global developmental delay, mild to moderate intellectual disability, brain anomalies, congenital heart defects, and dysmorphic features. Macrocephaly was a frequent but not universal finding. Additional common abnormalities included hypogonadism in males, skeletal and limb anomalies, hearing impairment, and ophthalmic abnormalities. The majority of variants were nontruncating and affected the SNF2-like region of the protein. We did not identify genotype–phenotype correlations based on the type or location of variants. Alterations in ATP hydrolysis and chromatin remodeling activities were observed in variants from different domains. The CHD4-related syndrome is a multisystemic neurodevelopmental disorder. Missense substitutions in different protein domains alter CHD4 function in a variant-specific manner, but result in a similar phenotype in humans.

Shohat-type spondyloepimetaphyseal dysplasia (SEMD) is a skeletal dysplasia that affects cartilage development. Similar skeletal disorders, such as spondyloepiphyseal dysplasias, are linked to mutations in type II collagen (COL2A1), but the causative gene in SEMD is not known. Here, we have performed whole-exome sequencing to identify a recurrent homozygous c.408+1G>A donor splice site loss-of-function mutation in DDRGK domain containing 1 (DDRGK1) in 4 families affected by SEMD. In zebrafish, ddrgk1 deficiency disrupted craniofacial cartilage development and led to decreased levels of the chondrogenic master transcription factor sox9 and its downstream target, col2a1. Overexpression of sox9 rescued the zebrafish chondrogenic and craniofacial phenotype generated by ddrgk1 knockdown, thus identifying DDRGK1 as a regulator of SOX9. Consistent with these results, Ddrgk1-/- mice displayed delayed limb bud chondrogenic condensation, decreased SOX9 protein expression and Col2a1 transcript levels, and increased apoptosis. Furthermore, we determined that DDRGK1 can directly bind to SOX9 to inhibit its ubiquitination and proteasomal degradation. Taken together, these data indicate that loss of DDRGK1 decreases SOX9 expression and causes a human skeletal dysplasia, identifying a mechanism that regulates chondrogenesis via modulation of SOX9 ubiquitination.

Background Mucopolysaccharidosis (MPS) IVA is a rare disease with substantial, multisystemic morbidity. We assessed real-world safety and effectiveness of the enzyme replacement therapy (ERT) elosulfase alfa in patients with MPS IVA in the multinational, observational Morquio A Registry Study (MARS) who initiated ERT in adulthood (aged ≥ 18 years). Methods Patients were enrolled between September 2014 and February 2022; urinary keratan sulfate (uKS), 6-minute walk test (6MWT) distance, forced expiratory volume in 1 s (FEV 1 ), forced vital capacity (FVC), EuroQoL-5D-5L (EQ-5D-5L) score, and safety were assessed during routine care. Results As of February 13, 2022, 90 patients who initiated ERT had enrolled (median exposure: 5.6 years; median age at first ERT: 27.8 years). Reductions from baseline in uKS levels were sustained over mean follow-up of 5.4 years (mean percent change: -52.9%; p  < 0.0001). In patients with available data, mean change in 6MWT distance was + 15.8 m ( p  = 0.3627) over a mean follow-up of 5.8 years. FEV 1 and FVC remained stable over mean follow-up of 5.3 years (mean change: 0.0 L for both). The mean change from baseline in EQ-5D-5L index score was + 0.1 after 1 year of treatment. Thirty-four patients (39.5%) had ≥ 1 adverse event (AE), 23 patients (26.7%) had ≥ 1 serious AE, and 10 (11.6%) had ≥ 1 drug-related AE (infusion-related reactions [ n  = 3; 3.5%], pyrexia [ n  = 2; 2.3%]). Eight deaths occurred; none were deemed treatment related. Conclusions Real-world data collected from MARS suggest that patients with MPS IVA who initiated ERT in adulthood remained stable over 7 years of follow-up. No new safety signals were identified.

CHARGE syndrome—which stands for coloboma of the eye, heart defects, atresia of choanae, retardation of growth/development, genital abnormalities, and ear anomalies—is a severe developmental disorder with wide phenotypic variability, caused mainly by mutations in CHD7 (chromodomain helicase DNA-binding protein 7), known to encode a chromatin remodeler. The genetic lesions responsible for CHD7 mutation-negative cases are unknown, at least in part because the pathogenic mechanisms underlying CHARGE syndrome remain poorly defined. Here, we report the characterization of a mouse model for CHD7 mutation-negative cases of CHARGE syndrome generated by insertional mutagenesis of Fam172a (family with sequence similarity 172, member A). We show that Fam172a plays a key role in the regulation of cotranscriptional alternative splicing, notably by interacting with Ago2 (Argonaute-2) and Chd7. Validation studies in a human cohort allow us to propose that dysregulation of cotranscriptional alternative splicing is a unifying pathogenic mechanism for both CHD7 mutation-positive and CHD7 mutation-negative cases. We also present evidence that such splicing defects can be corrected in vitro by acute rapamycin treatment.

Background Morquio A syndrome is a rare, autosomal recessive, progressively debilitating disorder, with multi-system impairments and high medical burden. Quebec, Canada has a large Morquio A population, which is considered unique due to the presence of founder pathogenic variants. The objectives of this study were to document the genetic and clinical heterogeneity of patients with Morquio A in Quebec, to better characterize the phenotype of those with the French Canadian founder pathogenic variant (NM_000512.5: c.1171A>G, p.Met391Val), and to describe the natural history of the patients treated with elosulfase alfa enzyme replacement therapy. Patients with Morquio A were genotyped for pathogenic variants in the lysosomal enzyme N -acetylgalactosamine-6-sulfatase. Clinical data were retrospectively collected from medical charts of patients and included medical history, height, physical examination, respiratory function tests, electrocardiogram, echocardiogram, endurance in the 6-min walk test (6MWT), and activities of daily living (ADL) as assessed by the Mucopolysaccharidosis Health Assessment Questionnaire (MPS-HAQ). Longitudinal data were collected retrospectively and prospectively for patients treated with elosulfase alfa. Results A total of 33 patients, aged 5–63 years, were included in the analysis. Patients with the founder pathogenic variant (n = 17) generally exhibited a non-classical form of Morquio A. As compared with patients with a non-founder pathogenic variant (n = 16), these patients were generally taller, had greater endurance and were better able to perform ADL. However, they still had significant musculoskeletal disease. Most of the 26 patients treated with elosulfase alfa, regardless of pathogenic variant, showed improvements in endurance and ADL. After 5 to 12 months of treatment, the mean improvement from baseline in the 6MWT was 23% and 10 of 14 patients improved in at least one MPS-HAQ domain. Endurance and ADL generally continued to improve or maintained stable in the long term (up to 7 years). Four out of 19 treated patients with echocardiogram data at follow-up showed progression of cardiac disease. Conclusions In Quebec, Canada, Morquio A frequently manifests as a non-classical form of the syndrome due to a founder effect. Patients treated with elosulfase alfa generally show long-term improvement or stability in endurance and function, regardless of pathogenic variant.