Eva-Lena Stattin

Clinical characterization of patients with autosomal dominant short stature due to aggrecan mutations

Context: Heterozygous mutations in the aggrecan gene (ACAN) cause autosomal dominant short stature with accelerated skeletal maturation. Objective: We sought to characterize the phenotypic spectrum and response to growth-promoting therapies. Patients and Methods: One hundred three individuals (57 females, 46 males) from 20 families with autosomal dominant short stature and heterozygous ACAN mutations were identified and confirmed using whole-exome sequencing, targeted next-generation sequencing, and/or Sanger sequencing. Clinical information was collected from the medical records. Results: Identified ACAN variants showed perfect cosegregation with phenotype. Adult individuals had mildly disproportionate short stature [median height, −2.8 standard deviation score (SDS); range, −5.9 to −0.9] and a history of early growth cessation. The condition was frequently associated with early-onset osteoarthritis (12 families) and intervertebral disc disease (9 families). No apparent genotype–phenotype correlation was found between the type of ACAN mutation and the presence of joint complaints. Childhood height was less affected (median height, −2.0 SDS; range, −4.2 to −0.6). Most children with ACAN mutations had advanced bone age (bone age − chronologic age; median, +1.3 years; range, +0.0 to +3.7 years). Nineteen individuals had received growth hormone therapy with some evidence of increased growth velocity. Conclusions: Heterozygous ACAN mutations result in a phenotypic spectrum ranging from mild and proportionate short stature to a mild skeletal dysplasia with disproportionate short stature and brachydactyly. Many affected individuals developed early-onset osteoarthritis and degenerative disc disease, suggesting dysfunction of the articular cartilage and intervertebral disc cartilage. Additional studies are needed to determine the optimal treatment strategy for these patients.

Chondrocytes Derived From Mesenchymal Stromal Cells and Induced Pluripotent Cells of Patients With Familial Osteochondritis Dissecans Exhibit an Endoplasmic Reticulum Stress Response and Defective Matrix Assembly

Familial osteochondritis dissecans (FOCD) is an inherited skeletal defect characterized by the development of large cartilage lesions in multiple joints, short stature, and early onset of severe osteoarthritis. It is associated with a heterozygous mutation in the ACAN gene, resulting in a Val‐Met replacement in the C‐type lectin domain of aggrecan. To understand the cellular pathogenesis of this condition, we studied the chondrogenic differentiation of patient bone marrow mesenchymal stromal cells (BM‐MSCs). We also looked at cartilage derived from induced pluripotent stem cells (iPSCs) generated from patient fibroblasts. Our results revealed several characteristics of the differentiated chondrocytes that help to explain the disease phenotype and susceptibility to cartilage injury. First, patient chondrogenic pellets had poor structural integrity but were rich in glycosaminoglycan. Second, it was evident that large amounts of aggrecan accumulated within the endoplasmic reticulum of chondrocytes differentiated from both BM‐MSCs and iPSCs. In turn, there was a marked absence of aggrecan in the extracellular matrix. Third, it was evident that matrix synthesis and assembly were globally dysregulated. These results highlight some of the abnormal aspects of chondrogenesis in these patient cells and help to explain the underlying cellular pathology. The results suggest that FOCD is a chondrocyte aggrecanosis with associated matrix dysregulation. The work provides a new in vitro model of osteoarthritis and cartilage degeneration based on the use of iPSCs and highlights how insights into disease phenotype and pathogenesis can be uncovered by studying differentiation of patient stem cells.

A novel approach using long-read sequencing and ddPCR to investigate gonadal mosaicism and estimate recurrence risk in two families with developmental disorders

De novo mutations contribute significantly to severe early‐onset genetic disorders. Even if the mutation is apparently de novo, there is a recurrence risk due to parental germ line mosaicism, depending on in which gonadal generation the mutation occurred.

Detailed analysis of HTT repeat elements in human blood using targeted amplification-free long-read sequencing

Amplification of DNA is required as a mandatory step during library preparation in most targeted sequencing protocols. This can be a critical limitation when targeting regions that are highly repetitive or with extreme guanine–cytosine (GC) content, including repeat expansions associated with human disease. Here, we used an amplification‐free protocol for targeted enrichment utilizing the CRISPR/Cas9 system (No‐Amp Targeted sequencing) in combination with single molecule, real‐time (SMRT) sequencing for studying repeat elements in the huntingtin (HTT) gene, where an expanded CAG repeat is causative for Huntington disease. We also developed a robust data analysis pipeline for repeat element analysis that is independent of alignment of reads to a reference genome. The method was applied to 11 diagnostic blood samples, and for all 22 alleles the resulting CAG repeat count agreed with previous results based on fragment analysis. The amplification‐free protocol also allowed for studying somatic variability of repeat elements in our samples, without the interference of PCR stutter. In summary, with No‐Amp Targeted sequencing in combination with our analysis pipeline, we could accurately study repeat elements that are difficult to investigate using PCR‐based methods.

A novel ECEL1 mutation expands the phenotype of distal arthrogryposis multiplex congenita type 5D to include pretibial vertical skin creases

Arthrogryposis multiplex congenita (AMC) is a heterogeneous disorder characterized by multiple joint contractures often in association with other congenital abnormalities. Pretibial linear vertical creases are a rare finding associated with arthrogryposis, and the etiology of the specific condition is unknown. We aimed to genetically and clinically characterize a boy from a consanguineous family, presenting with AMC and pretibial vertical linear creases on the shins. Whole exome sequencing and variant analysis revealed homozygous novel missense variants of ECEL1 (c.1163Tu2009>u2009C, p.Leu388Pro, NM_004826) and MUSK (c.2572Cu2009>u2009T, p.Arg858Cys, NM_005592). Both variants are predicted to have deleterious effects on the protein function, with amino acid positions highly conserved among species. The variants segregated in the family, with healthy mother, father, and sister being heterozygous carriers and the index patient being homozygous for both mutations. We report on a unique patient with a novel ECEL1 homozygous mutation, expanding the phenotypic spectrum of Distal AMC Type 5D to include vertical linear skin creases. The homozygous mutation in MUSK is of unknown clinical significance. MUSK mutations have previously shown to cause congenital myasthenic syndrome, a neuromuscular disorder with defects in the neuromuscular junction.

Generation of induced pluripotent stem cells (ARO-iPSC1-11) from a patient with autosomal recessive osteopetrosis harboring the c.212 + 1G > T mutation in SNX10 gene

Pathogenic sequence variants in the Sorting Nexin 10 (SNX10) gene have been associated with autosomal recessive osteopetrosis (ARO) in human. In this study, an induced pluripotent stem cell (iPSC) line (ARO-iPSC1-11) was generated from an ARO patient carrying the homozygous c.212+1G>T mutation in SNX10, using a retroviral-based reprogramming protocol. Characterization confirmed that the generated iPSCs expressed pluripotency markers, displayed normal karyotype, showed pluripotent differentiation capacity and retained the targeted mutation. Disease modeling with this ARO patient-specific iPSC line will shed further light on the critical role of the SNX10 mutation in ARO development.

Unravelling the mystery behind sudden death in the young - a wake-up call for nationwide autopsy-based approach: authors' reply.

Unravelling the mystery behind sudden death in the young : a wake-up call for nationwide autopsy-based approach - Authors reply

Sex is a moderator of the association between NOS1AP sequence variants and QTc in two long QT syndrome founder populations : a pedigree-based measured genotype association analysis

BackgroundSequence variants in the NOS1AP gene have repeatedly been reported to influence QTc, albeit with moderate effect sizes. In the long QT syndrome (LQTS), this may contribute to the substantial QTc variance seen among carriers of identical pathogenic sequence variants. Here we assess three non-coding NOS1AP sequence variants, chosen for their previously reported strong association with QTc in normal and LQTS populations, for association with QTc in two Swedish LQT1 founder populations.MethodsThis study included 312 individuals (58% females) from two LQT1 founder populations, whereof 227 genotype positive segregating either Y111C (nxa0=xa0148) or R518* (nxa0=xa079) pathogenic sequence variants in the KCNQ1 gene, and 85 genotype negatives. All were genotyped for NOS1AP sequence variants rs12143842, rs16847548 and rs4657139, and tested for association with QTc length (effect size presented as mean difference between derived and wildtype, in ms), using a pedigree-based measured genotype association analysis. Mean QTc was obtained by repeated manual measurement (preferably in lead II) by one observer using coded 50xa0mm/s standard 12-lead ECGs.ResultsA substantial variance in mean QTc was seen in genotype positives 476xa0±xa036xa0ms (Y111C 483xa0±xa034xa0ms; R518* 462xa0±xa034xa0ms) and genotype negatives 433xa0±xa024xa0ms. Female sex was significantly associated with QTc prolongation in all genotype groups (pxa0<xa00.001). In a multivariable analysis including the entire study population and adjusted for KCNQ1 genotype, sex and age, NOS1AP sequence variants rs12143842 and rs16847548 (but not rs4657139) were significantly associated with QT prolongation, +18xa0ms (pxa0=xa00.0007) and +17xa0ms (pxa0=xa00.006), respectively. Significant sex-interactions were detected for both sequent variants (interaction term rxa0=xa00.892, pxa0<xa00.001 and rxa0=xa00.944, pxa0<xa00.001, respectively). Notably, across the genotype groups, when stratified by sex neither rs12143842 nor rs16847548 were significantly associated with QTc in females (both pxa0=xa00.16) while in males, a prolongation of +19xa0ms and +8xa0ms (pxa0=xa00.002 and pxa0=xa00.02) was seen in multivariable analysis, explaining up to 23% of QTc variance in all males.ConclusionsSex was identified as a moderator of the association between NOS1AP sequence variants and QTc in two LQT1 founder populations. This finding may contribute to QTc sex differences and affect the usefulness of NOS1AP as a marker for clinical risk stratification in LQTS.