Competition between maturation and degradation drives human snRNA 3' end quality control.

Polymerases and exonucleases act on 3' ends of nascent RNAs to promote their maturation or degradation but how the balance between these activities is controlled to dictate the fates of cellular RNAs remains poorly understood. Here, we identify a central role for the human DEDD deadenylase TOE1 in distinguishing the fates of small nuclear (sn)RNAs of the spliceosome from unstable genome-encoded snRNA variants. We found that TOE1 promotes maturation of all regular RNA polymerase II transcribed snRNAs of the major and minor spliceosomes by removing posttranscriptional oligo(A) tails, trimming 3' ends, and preventing nuclear exosome targeting. In contrast, TOE1 promotes little to no maturation of tested U1 variant snRNAs, which are instead targeted by the nuclear exosome. These observations suggest that TOE1 is positioned at the center of a 3' end quality control pathway that selectively promotes maturation and stability of regular snRNAs while leaving snRNA variants unprocessed and exposed to degradation in what could be a widespread mechanism of RNA quality control given the large number of noncoding RNAs processed by DEDD deadenylases.

Haplotype-based analysis resolves missing heritability in oculocutaneous albinism type 1B.

Oculocutaneous albinism (OCA) is a rare disorder of pigment production. Affected individuals have variably decreased global pigmentation and visual-developmental changes that lead to low vision. OCA is notable for significant missing heritability, particularly among individuals with residual pigmentation. Tyrosinase (TYR) is the rate-limiting enzyme in melanin pigment biosynthesis and mutations that decrease enzyme function are one of the most common causes of OCA. We present the analysis of high-depth short-read TYR sequencing data for a cohort of 352 OCA probands, ∼50% of whom were previously sequenced without yielding a definitive diagnostic result. Our analysis identified 66 TYR single-nucleotide variants (SNVs) and small insertion/deletions (indels), 3 structural variants, and a rare haplotype comprised of two common frequency variants (p.Ser192Tyr and p.Arg402Gln) in cis-orientation, present in 149/352 OCA probands. We further describe a detailed analysis of the disease-causing haplotype, p.[Ser192Tyr; Arg402Gln] ("cis-YQ"). Haplotype analysis suggests that the cis-YQ allele arose by recombination and that multiple cis-YQ haplotypes are segregating in OCA-affected individuals and control populations. The cis-YQ allele is the most common disease-causing allele in our cohort, representing 19.1% (57/298) of TYR pathogenic alleles in individuals with type 1 (TYR-associated) OCA. Finally, among the 66 TYR variants, we found several additional alleles defined by a cis-oriented combination of minor, potentially hypomorph-producing alleles at common variant sites plus a second, rare pathogenic variant. Together, these results suggest that identification of phased variants for the full TYR locus are required for an exhaustive assessment for potentially disease-causing alleles.

IMPDH2 filaments protect from neurodegeneration in AMPD2 deficiency.

Metabolic dysregulation is one of the most common causes of pediatric neurodegenerative disorders. However, how the disruption of ubiquitous and essential metabolic pathways predominantly affect neural tissue remains unclear. Here we use mouse models of a childhood neurodegenerative disorder caused by AMPD2 deficiency to study cellular and molecular mechanisms that lead to selective neuronal vulnerability to purine metabolism imbalance. We show that mouse models of AMPD2 deficiency exhibit predominant degeneration of the hippocampal dentate gyrus, despite a general reduction of brain GTP levels. Neurodegeneration-resistant regions accumulate micron-sized filaments of IMPDH2, the rate limiting enzyme in GTP synthesis, while these filaments are barely detectable in the hippocampal dentate gyrus. Furthermore, we show that IMPDH2 filament disassembly reduces GTP levels and impairs growth of neural progenitor cells derived from individuals with human AMPD2 deficiency. Together, our findings suggest that IMPDH2 polymerization prevents detrimental GTP deprivation, opening the possibility of exploring the induction of IMPDH2 assembly as a therapy for neurodegeneration.

FAM91A1-TBC1D23 complex structure reveals human genetic variations susceptible for PCH.

Pontocerebellar hypoplasia (PCH) is a group of rare neurodevelopmental disorders with limited diagnostic and therapeutic options. Mutations in WDR11, a subunit of the FAM91A1 complex, have been found in patients with PCH-like symptoms; however, definitive evidence that the mutations are causal is still lacking. Here, we show that depletion of FAM91A1 results in developmental defects in zebrafish similar to that of TBC1D23, an established PCH gene. FAM91A1 and TBC1D23 directly interact with each other and cooperate to regulate endosome-to-Golgi trafficking of KIAA0319L, a protein known to regulate axonal growth. Crystal structure of the FAM91A1-TBC1D23 complex reveals that TBC1D23 binds to a conserved surface on FAM91A1 by assuming a Z-shaped conformation. More importantly, the interaction between FAM91A1 and TBC1D23 can be used to predict the risk of certain TBC1D23-associated mutations to PCH. Collectively, our study provides a molecular basis for the interaction between TBC1D23 and FAM91A1 and suggests that disrupted endosomal trafficking underlies multiple PCH subtypes.

A transchromosomic rat model with human chromosome 21 shows robust Down syndrome features.

Progress in earlier detection and clinical management has increased life expectancy and quality of life in people with Down syndrome (DS). However, no drug has been approved to help individuals with DS live independently and fully. Although rat models could support more robust physiological, behavioral, and toxicology analysis than mouse models during preclinical validation, no DS rat model is available as a result of technical challenges. We developed a transchromosomic rat model of DS, TcHSA21rat, which contains a freely segregating, EGFP-inserted, human chromosome 21 (HSA21) with >93% of its protein-coding genes. RNA-seq of neonatal forebrains demonstrates that TcHSA21rat expresses HSA21 genes and has an imbalance in global gene expression. Using EGFP as a marker for trisomic cells, flow cytometry analyses of peripheral blood cells from 361 adult TcHSA21rat animals show that 81% of animals retain HSA21 in >80% of cells, the criterion for a "Down syndrome karyotype" in people. TcHSA21rat exhibits learning and memory deficits and shows increased anxiety and hyperactivity. TcHSA21rat recapitulates well-characterized DS brain morphology, including smaller brain volume and reduced cerebellar size. In addition, the rat model shows reduced cerebellar foliation, which is not observed in DS mouse models. Moreover, TcHSA21rat exhibits anomalies in craniofacial morphology, heart development, husbandry, and stature. TcHSA21rat is a robust DS animal model that can facilitate DS basic research and provide a unique tool for preclinical validation to accelerate DS drug development.

Recessive PRDM13 mutations cause fatal perinatal brainstem dysfunction with cerebellar hypoplasia and disrupt Purkinje cell differentiation.

Pontocerebellar hypoplasias (PCHs) are congenital disorders characterized by hypoplasia or early atrophy of the cerebellum and brainstem, leading to a very limited motor and cognitive development. Although over 20 genes have been shown to be mutated in PCHs, a large proportion of affected individuals remains undiagnosed. We describe four families with children presenting with severe neonatal brainstem dysfunction and pronounced deficits in cognitive and motor development associated with four different bi-allelic mutations in PRDM13, including homozygous truncating variants in the most severely affected individuals. Brain MRI and fetopathological examination revealed a PCH-like phenotype, associated with major hypoplasia of inferior olive nuclei and dysplasia of the dentate nucleus. Notably, histopathological examinations highlighted a sparse and disorganized Purkinje cell layer in the cerebellum. PRDM13 encodes a transcriptional repressor known to be critical for neuronal subtypes specification in the mouse retina and spinal cord but had not been implicated, so far, in hindbrain development. snRNA-seq data mining and in situ hybridization in humans show that PRDM13 is expressed at early stages in the progenitors of the cerebellar ventricular zone, which gives rise to cerebellar GABAergic neurons, including Purkinje cells. We also show that loss of function of prdm13 in zebrafish leads to a reduction in Purkinje cells numbers and a complete absence of the inferior olive nuclei. Altogether our data identified bi-allelic mutations in PRDM13 as causing a olivopontocerebellar hypoplasia syndrome and suggest that early deregulations of the transcriptional control of neuronal fate specification could contribute to a significant number of cases.

Single-cell transcriptomic signatures and gene regulatory networks modulated by Wls in mammalian midline facial formation and clefts.

Formation of highly unique and complex facial structures is controlled by genetic programs that are responsible for the precise coordination of three-dimensional tissue morphogenesis. However, the underlying mechanisms governing these processes remain poorly understood. We combined mouse genetic and genomic approaches to define the mechanisms underlying normal and defective midfacial morphogenesis. Conditional inactivation of the Wnt secretion protein Wls in Pax3-expressing lineage cells disrupted frontonasal primordial patterning, cell survival and directional outgrowth, resulting in altered facial structures, including midfacial hypoplasia and midline facial clefts. Single-cell RNA sequencing revealed unique transcriptomic atlases of mesenchymal subpopulations in the midfacial primordia, which are disrupted in the conditional Wls mutants. Differentially expressed genes and cis-regulatory sequence analyses uncovered that Wls modulates and integrates a core gene regulatory network, consisting of key midfacial regulatory transcription factors (including Msx1, Pax3 and Pax7) and their downstream targets (including Wnt, Shh, Tgfß and retinoic acid signaling components), in a mesenchymal subpopulation of the medial nasal prominences that is responsible for midline facial formation and fusion. These results reveal fundamental mechanisms underlying mammalian midfacial morphogenesis and related defects at single-cell resolution.

Deletion of RFX6 impairs iPSC-derived islet organoid development and survival, with no impact on PDX1+/NKX6.1+ progenitors.

AIMS/HYPOTHESIS: Homozygous mutations in RFX6 lead to neonatal diabetes accompanied by a hypoplastic pancreas, whereas heterozygous mutations cause MODY. Recent studies have also shown RFX6 variants to be linked with type 2 diabetes. Despite RFX6's known function in islet development, its specific role in diabetes pathogenesis remains unclear. Here, we aimed to understand the mechanisms underlying the impairment of pancreatic islet development and subsequent hypoplasia due to loss-of-function mutations in RFX6. METHODS: We examined regulatory factor X6 (RFX6) expression during human embryonic stem cell (hESC) differentiation into pancreatic islets and re-analysed a single-cell RNA-seq dataset to identify RFX6-specific cell populations during islet development. Furthermore, induced pluripotent stem cell (iPSC) lines lacking RFX6 were generated using CRISPR/Cas9. Various approaches were then employed to explore the consequences of RFX6 loss across different developmental stages. Subsequently, we evaluated transcriptional changes resulting from RFX6 loss through RNA-seq of pancreatic progenitors (PPs) and endocrine progenitors (EPs). RESULTS: RFX6 expression was detected in PDX1+ cells in the hESC-derived posterior foregut (PF). However, in the PPs, RFX6 did not co-localise with pancreatic and duodenal homeobox 1 (PDX1) or NK homeobox 1 (NKX6.1) but instead co-localised with neurogenin 3, NK2 homeobox 2 and islet hormones in the EPs and islets. Single-cell analysis revealed high RFX6 expression levels in endocrine clusters across various hESC-derived pancreatic differentiation stages. Upon differentiating iPSCs lacking RFX6 into pancreatic islets, a significant decrease in PDX1 expression at the PF stage was observed, although this did not affect PPs co-expressing PDX1 and NKX6.1. RNA-seq analysis showed the downregulation of essential genes involved in pancreatic endocrine differentiation, insulin secretion and ion transport due to RFX6 deficiency. Furthermore, RFX6 deficiency resulted in the formation of smaller islet organoids due to increased cellular apoptosis, linked to reduced catalase expression, implying a protective role for RFX6. Overexpression of RFX6 reversed defective phenotypes in RFX6-knockout PPs, EPs and islets. CONCLUSIONS/INTERPRETATION: These findings suggest that pancreatic hypoplasia and reduced islet cell formation associated with RFX6 mutations are not due to alterations in PDX1+/NKX6.1+ PPs but instead result from cellular apoptosis and downregulation of pancreatic endocrine genes. DATA AVAILABILITY: RNA-seq datasets have been deposited in the Zenodo repository with accession link (DOI: https://doi.org/10.5281/zenodo.10656891 ).

Direct thrombin inhibitors fail to reverse the negative effects of heparin on lung growth and function after murine left pneumonectomy.

Neonates with congenital diaphragmatic hernia (CDH) frequently require cardiopulmonary bypass and systemic anticoagulation. We previously demonstrated that even subtherapeutic heparin impairs lung growth and function in a murine model of compensatory lung growth (CLG). The direct thrombin inhibitors (DTIs) bivalirudin and argatroban preserved growth in this model. Although DTIs are increasingly used for systemic anticoagulation clinically, patients with CDH may still receive heparin. In this experiment, lung endothelial cell proliferation was assessed following treatment with heparin-alone or mixed with increasing concentrations of bivalirudin or argatroban. The effects of subtherapeutic heparin with or without DTIs in the CLG model were also investigated. C57BL/6J mice underwent left pneumonectomy and subcutaneous implantation of osmotic pumps. Pumps were preloaded with normal saline, bivalirudin, or argatroban; treated animals received daily intraperitoneal low-dose heparin. In vitro, heparin-alone decreased endothelial cell proliferation and increased apoptosis. The effect of heparin on proliferation, but not apoptosis, was reversed by the addition of bivalirudin and argatroban. In vivo, low-dose heparin decreased lung volume compared with saline-treated controls. All three groups that received heparin demonstrated decreased lung function on pulmonary function testing and impaired exercise performance on treadmill tolerance testing. These findings correlated with decreases in alveolarization, vascularization, angiogenic signaling, and gene expression in the heparin-exposed groups. Together, these data suggest that bivalirudin and argatroban fail to reverse the inhibitory effects of subtherapeutic heparin on lung growth and function. Clinical studies on the impact of low-dose heparin with DTIs on CDH outcomes are warranted.NEW & NOTEWORTHY Infants with pulmonary hypoplasia frequently require cardiopulmonary bypass and systemic anticoagulation. We investigate the effects of simultaneous exposure to heparin and direct thrombin inhibitors (DTIs) on lung growth and pulmonary function in a murine model of compensatory lung growth (CGL). Our data suggest that DTIs fail to reverse the inhibitory effects of subtherapeutic heparin on lung growth and function. Clinical studies on the impact of heparin with DTIs on clinical outcomes are thus warranted.

Implication of transcription factor FOXD2 dysfunction in syndromic congenital anomalies of the kidney and urinary tract (CAKUT).

Congenital anomalies of the kidney and urinary tract (CAKUT) are the predominant cause for chronic kidney disease below age 30 years. Many monogenic forms have been discovered due to comprehensive genetic testing like exome sequencing. However, disease-causing variants in known disease-associated genes only explain a proportion of cases. Here, we aim to unravel underlying molecular mechanisms of syndromic CAKUT in three unrelated multiplex families with presumed autosomal recessive inheritance. Exome sequencing in the index individuals revealed three different rare homozygous variants in FOXD2, encoding a transcription factor not previously implicated in CAKUT in humans: a frameshift in the Arabic and a missense variant each in the Turkish and the Israeli family with segregation patterns consistent with autosomal recessive inheritance. CRISPR/Cas9-derived Foxd2 knockout mice presented with a bilateral dilated kidney pelvis accompanied by atrophy of the kidney papilla and mandibular, ophthalmologic, and behavioral anomalies, recapitulating the human phenotype. In a complementary approach to study pathomechanisms of FOXD2-dysfunction-mediated developmental kidney defects, we generated CRISPR/Cas9-mediated knockout of Foxd2 in ureteric bud-induced mouse metanephric mesenchyme cells. Transcriptomic analyses revealed enrichment of numerous differentially expressed genes important for kidney/urogenital development, including Pax2 and Wnt4 as well as gene expression changes indicating a shift toward a stromal cell identity. Histology of Foxd2 knockout mouse kidneys confirmed increased fibrosis. Further, genome-wide association studies suggest that FOXD2 could play a role for maintenance of podocyte integrity during adulthood. Thus, our studies help in genetic diagnostics of monogenic CAKUT and in understanding of monogenic and multifactorial kidney diseases.

Position effects at the FGF8 locus are associated with femoral hypoplasia.

Copy-number variations (CNVs) are a common cause of congenital limb malformations and are interpreted primarily on the basis of their effect on gene dosage. However, recent studies show that CNVs also influence the 3D genome chromatin organization. The functional interpretation of whether a phenotype is the result of gene dosage or a regulatory position effect remains challenging. Here, we report on two unrelated families with individuals affected by bilateral hypoplasia of the femoral bones, both harboring de novo duplications on chromosome 10q24.32. The ∼0.5 Mb duplications include FGF8, a key regulator of limb development and several limb enhancer elements. To functionally characterize these variants, we analyzed the local chromatin architecture in the affected individuals' cells and re-engineered the duplications in mice by using CRISPR-Cas9 genome editing. We found that the duplications were associated with ectopic chromatin contacts and increased FGF8 expression. Transgenic mice carrying the heterozygous tandem duplication including Fgf8 exhibited proximal shortening of the limbs, resembling the human phenotype. To evaluate whether the phenotype was a result of gene dosage, we generated another transgenic mice line, carrying the duplication on one allele and a concurrent Fgf8 deletion on the other allele, as a control. Surprisingly, the same malformations were observed. Capture Hi-C experiments revealed ectopic interaction with the duplicated region and Fgf8, indicating a position effect. In summary, we show that duplications at the FGF8 locus are associated with femoral hypoplasia and that the phenotype is most likely the result of position effects altering FGF8 expression rather than gene dosage effects.

Congenital Diaphragmatic Hernia Patients with Left Heart Hypoplasia and Left Ventricular Dysfunction Have Highest Odds of Mortality.

OBJECTIVES: To describe the scope of left ventricular (LV) dysfunction and left heart hypoplasia (LHH) in infants with congenital diaphragmatic hernia (CDH), to determine associations with CDH severity, and to evaluate the odds of extracorporeal membrane oxygenation (ECMO) and death with categories of left heart disease. STUDY DESIGN: Demographic and clinical variables were collected from a single-center, retrospective cohort of patients with CDH from January 2017 through May 2022. Quantitative measures of LV function and LHH were prospectively performed on initial echocardiograms. LHH was defined as ≥2 of the following: z score ≤ -2 of any left heart structure or LV end-diastolic volume <3 mL. LV dysfunction was defined as shortening fraction <28%, ejection fraction <60%, or global longitudinal strain <20%. The exposure was operationalized as a 4-group categorical variable (LV dysfunction +/-, LHH +/-). Logistic regression models evaluated associations with ECMO and death, adjusting for CDH severity. RESULTS: One hundred eight-two patients (80.8% left CDH, 63.2% liver herniation, 23.6% ECMO, 12.1% mortality) were included. Twenty percent demonstrated normal LV function and no LHH (LV dysfunction-/LHH-), 37% normal LV function with LHH (LV dysfunction-/LHH+), 14% LV dysfunction without LHH (LV dysfunction+/LHH-), and 28% both LV dysfunction and LHH (LV dysfunction+/LHH+). There was a dose-response effect between increasing severity of left heart disease, ECMO use, and mortality. LV dysfunction+/LHH + infants had the highest odds of ECMO use and death, after adjustment for CDH severity [OR (95% CI); 1.76 (1.20, 2.62) for ECMO, 2.76 (1.63, 5.17) for death]. CONCLUSIONS: In our large single-center cohort, patients with CDH with LV dysfunction+/LHH + had the highest risk of ECMO use and death.

RUNX2-related metaphyseal dysplasia with maxillary hypoplasia: A rare skeletal disorder resembling SFRP4-related Pyle disease.

Metaphyseal dysplasia with maxillary hypoplasia with or without brachydactyly (MDMHB) is an ultra-rare skeletal dysplasia caused by heterozygous intragenic RUNX2 duplications, comprising either exons 3 to 5 or exons 3 to 6 of RUNX2. In this study, we describe a 14-year-old Belgian boy with metaphyseal dysplasia with maxillary hypoplasia but without brachydactyly. Clinical and radiographic examination revealed mild facial dysmorphism, dental anomalies, enlarged clavicles, genua valga and metaphyseal flaring and thin cortices with an osteoporotic skeletal appearance. Exome sequencing led to the identification of a de novo heterozygous tandem duplication within RUNX2, encompassing exons 3 to 7. This duplication is larger than the ones previously reported in MDMHB cases since it extends into the C-terminal activation domain of RUNX2. We review previously reported cases with MDMHB and highlight the resemblance of this disorder with Pyle disease, which may be explained by intersecting molecular pathways between RUNX2 and sFRP4. This study expands our knowledge on the genotypic and phenotypic characteristics of MDMHB and the role of RUNX2 in rare bone disorders.

Cyclic loading failed to promote growth in a pig model of midfacial hypoplasia.

Yucatan miniature pigs, often used as large animal models in clinical research, are distinguished by a breed-specific midfacial hypoplasia with anterior crossbite. Although this deformity can be corrected by distraction osteogenesis, a less invasive method is desirable. We chose a mechanical cyclic stimulation protocol that has been successful in enhancing sutural growth in small animals and in a pilot study on standard pigs. Yucatan minipigs (n = 14) were obtained in pairs, with one of each pair randomly assigned to sham or loaded groups. All animals had loading implants installed on the right nasal and frontal bones and received labels for cell proliferation and mineral apposition. After a week of healing and under anesthesia, experimental animals received cyclic tensile loads (2.5 Hz, 30 min) delivered to the right nasofrontal suture daily for 5 days. Sutural strains were recorded at the final session for experimental animals. Sham animals received the same treatment except without loading or strain gauge placement. In contrast to pilot results on standard pigs, the treatment did not produce the expected sutural widening and increased growth. Although sutures were not fused and strains were in the normal range, the targeted right nasofrontal suture was narrowed rather than widened, with no statistically significant changes in sutural cell proliferation, mineral apposition, or vascularity. In general, Yucatan minipig sutures were more vascular than those of standard pigs and also tended to have more proliferating cells. In conclusion, either because the sutures themselves are abnormal or because of growth restrictions elsewhere in the skull, this cyclic loading protocol was unable to produce the desired response of sutural widening and growth. This treatment, effective in normal animals, did not improve naturally occurring midfacial hypoplasia in Yucatan minipigs.

Pituitary deficiencies related to optic nerve hypoplasia and visual acuity.

OBJECTIVE: Optic nerve hypoplasia (ONH), the congenital underdevelopment of the optic nerve, is an increasing cause of visual impairment and is associated with pituitary dysfunction. Past studies have focused on the relationship between ONH, pituitary deficiencies, and brain imaging. However, recent studies have demonstrated the true risk for hypopituitarism lies with the presence or absence of ONH, irrespective of midline brain findings. This study reviewed the relationship between the health of the optic nerve (visual acuity) and pituitary gland (number and age of development of pituitary deficiencies) as a way to stratify risk, regardless of imaging findings. DESIGN, PATIENTS AND MEASUREMENTS: Retrospective chart review of 197 patients seen at a single center from 2013 to 2022. Visual assessment was defined by distance acuity, and the presence of nystagmus or afferent pupillary defect. Pituitary deficiencies were diagnosed per Endocrine Society guidelines. RESULTS: In children with bilateral ONH (bONH), profound visual impairment was associated with more pituitary deficiencies between 0 and 15 years of age. The odds of having any pituitary deficiency were 4.9 times higher (95% confidence interval [95% CI]: 2.4-10.1) for patients with bONH versus unilateral ONH (uONH). Central hypothyroidism was the most common first presenting pituitary deficiency followed by growth hormone across all patients. CONCLUSION: This study shows a significant association between severity of visual impairment and increased probability of pituitary deficiencies in children with bONH versus uONH. Children with ONH require urgent endocrine evaluation due to risk of pituitary deficiencies, but risk stratification may also be based on severity of visual impairment.

Simultaneous loss of skeletal muscle myosin heavy chain IIx and IIb causes severe skeletal muscle hypoplasia in postnatal mice.

The skeletal muscle myosin heavy chain (MyHC) is a fundamental component of the sarcomere structure and muscle contraction. Two of the three adult fast MyHCs, MyHC-IIx and MyHC-IIb, are encoded by Myh1 and Myh4, respectively. However, skeletal muscle disorders have not yet been linked to these genes in humans. MyHC-IIb is barely detectable in human skeletal muscles. Thus, to characterize the molecular function of skeletal muscle MyHCs in humans, investigation of the effect of simultaneous loss of MyHC-IIb and other MyHCs on skeletal muscle in mice is essential. Here, we generated double knockout (dKO) mice with simultaneous loss of adult fast MyHCs by introducing nonsense frameshift mutations into the Myh1 and Myh4 genes. The dKO mice appeared normal after birth and until 2 weeks of age but showed severe skeletal muscle hypoplasia after 2 weeks. In 3-week-old dKO mice, increased expression of other skeletal muscle MyHCs, such as MyHC-I, MyHC-IIa, MyHC-neo, and MyHC-emb, was observed. However, these expressions were not sufficient to compensate for the loss of MyHC-IIb and MyHC-IIx. Moreover, the aberrant sarcomere structure with altered expression of sarcomere components was observed in dKO mice. Our findings imply that the simultaneous loss of MyHC-IIb and MyHC-IIx is substantially detrimental to postnatal skeletal muscle function and will contribute to elucidating the molecular mechanisms of skeletal muscle wasting disorders caused by the loss of skeletal muscle MyHCs.

Evaluation of the Patients with the Diagnosis of Pontocerebellar Hypoplasia: A Multicenter National Study.

Pontocerebellar hypoplasia (PCH) is a heterogeneous group of neurodegenerative disorders characterized by hypoplasia and degeneration of the cerebellum and pons. We aimed to identify the clinical, laboratory, and imaging findings of the patients with diagnosed PCH with confirmed genetic analysis. We collected available clinical data, laboratory, and imaging findings in our retrospective multicenter national study of 64 patients with PCH in Turkey. The genetic analysis included the whole-exome sequencing (WES), targeted next-generation sequencing (NGS), or single gene analysis. Sixty-four patients with PCH were 28 female (43.8%) and 36 (56.3%) male. The patients revealed homozygous mutation in 89.1%, consanguinity in 79.7%, pregnancy at term in 85.2%, microcephaly in 91.3%, psychomotor retardation in 98.4%, abnormal neurological findings in 100%, seizure in 63.8%, normal biochemistry and metabolic investigations in 92.2%, and dysmorphic findings in 51.2%. The missense mutation was found to be the most common variant type in all patients with PCH. It was detected as CLP1 (n = 17) was the most common PCH related gene. The homozygous missense variant c.419G > A (p.Arg140His) was identified in all patients with CLP1. Moreover, all patients showed the same homozygous missense variant c.919G > T (p.A307S) in TSEN54 group (n = 6). In Turkey, CLP1 was identified as the most common causative gene with the identical variant c.419G > A; p.Arg140His. The current study supports that genotype data on PCH leads to phenotypic variability over a wide phenotypic spectrum.

Classic "PCH" Genes are a Rare Cause of Radiologic Pontocerebellar Hypoplasia.

The term Pontocerebellar Hypoplasia (PCH) was initially used to designate a heterogeneous group of fetal-onset genetic neurodegenerative disorders. As a descriptive term, PCH refers to pons and cerebellum of reduced volume. In addition to the classic PCH types described in OMIM, many other disorders can result in a similar imaging appearance. This study aims to review imaging, clinical and genetic features and underlying etiologies of a cohort of children with PCH on imaging. We systematically reviewed brain images and clinical charts of 38 patients with radiologic evidence of PCH. Our cohort included 21 males and 17 females, with ages ranging between 8 days to 15 years. All individuals had pons and cerebellar vermis hypoplasia, and 63% had cerebellar hemisphere hypoplasia. Supratentorial anomalies were found in 71%. An underlying etiology was identified in 68% and included chromosomal (21%), monogenic (34%) and acquired (13%) causes. Only one patient had pathogenic variants in an OMIM listed PCH gene. Outcomes were poor regardless of etiology, though no one had regression. Approximately one third of patients deceased at a median age of 8 months. All individuals had global developmental delay, 50% were non-verbal, 64% were non-ambulatory and 45% required gastrostomy feeding. This cohort demonstrates that radiologic PCH has heterogenous etiologies and the "classic" OMIM-listed PCH genes underlie only a minority of cases. Broad genetic testing, including chromosomal microarray and exome or multigene panels, is recommended in individuals with PCH-like imaging appearance. Our results strongly suggest that the term PCH should be used to designate radiologic findings, and not to imply neurogenerative disorders.

Undifferentiated psychosis or schizophrenia associated with vermis-predominant cerebellar hypoplasia.

Schizophrenia (SCZ) is a well-studied neuropsychiatric condition that has been shown to have a high degree of genetic heritability. Still, little data on the specific genetic risk variants associated with the disease exists. Classification of the SCZ phenotype into SCZ-related endophenotypes is a promising methodology to parse out and elucidate the specific genetic risk variants for each. Here, we present a series of 17 previously reported individuals and a new proband with similar SCZ-related neuropsychiatric characteristics and shared brain imaging findings. Unsurprisingly, these individuals shared classic psychiatric features of SCZ. Interestingly, we also identified shared neuropsychiatric features in this series of individuals that had not been highlighted previously. A consistently decreased IQ, memory impairment, sleep and speech disturbances, and attention deficits were commonly reported findings. The brain imaging findings among these individuals also consistently showed posterior vermis predominant cerebellar hypoplasia (CBLH-V). Most individuals' diagnoses were initially described as Dandy-Walker malformation; however, our independent review of imaging suggests a more consistent pattern of posterior vermis predominant cerebellar hypoplasia rather than true Dandy-Walker malformation. While the specific genetic risk variants for this endophenotype are yet to be described, the aim of this paper is to present the shared neuropsychiatric features and consistent, symmetrical brain image findings which suggest that this subset of individuals comprises an endophenotype of SCZ with a high genetic solve rate.

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".