Myopathy associated with homozygous PYROXD1 pathogenic variants detected by genome sequencing

PYROXD1-associated myopathy

PYROXD1-associated myopathy is a rare genetic form of limb-girdle muscular dystrophy (LGMD) with only 23 previous cases having been reported in the literature. The exact role of PYROXD1 in the pathophysiology of LGMD remains unclear. We describe two brothers who presented to the neuromuscular clinic with progressive weakness of their upper and lower limbs over the preceding decades. Our case highlights how recent advancements in genetic sequencing have revolutionised the diagnostic classification process for LGMD and provided opportunities to establish diagnoses for previously unclassified myopathies. We also illustrate how the increased adoption of muscle MRI to identify disease and target muscle biopsy can provide better quality and more informative samples for classification. Finally, our report details the clinical and histopathological findings found in both cases adding valuable data to the currently limited information published on PYROXD1-associated myopathy.

Crosstalk between ROCK1 and PYROXD1 regulates CAFs activation and promotes laryngeal squamous cell carcinoma metastasis

We previously found that the Rho-associated kinase 1 (ROCK1) activated Cancer-associated fibroblasts (CAFs) to promote LSCC metastasis. Accumulating evidence indicates that pyridine nucleotide-disulfide oxidoreductase domain 1 (PYROXD1) is an oncogene; however, the crosstalk between ROCK1 and PYROXD1 in LSCC metastasis remains largely unknown. Here, we found that ROCK1 could target PYROXD1. The knockdown of ROCK1 expression reduces the expression of PYROXD1, while the knockdown of PYROXD1 expression did not alter the expression of ROCK1 indicating that ROCK1 is upstream of PYROXD1. Further, LSCC cells cocultured with PYROXD1 knocked-down CAFs exhibited lower proliferation, migration, invasion and metastasis abilities. Conversely, LSCC cells cocultured with PYROXD1-overexpressing CAFs showed opposite results. In conclusion, the crosstalk between ROCK1 and PYROXD1 regulated CAFs activation and promoted LSCC metastasis.

Clinical and genetic characterization of PYROXD1-related myopathy patients from Turkey

Congenital myopathies (CMs) are a heterogeneous group of inherited muscle disorders characterized by muscle weakness at birth, while limb-girdle muscular dystrophies (LGMD) have a later onset and slower disease progression. Thus, detailed clinical phenotyping of genetically defined disease entities are required for the full understanding of genotype-phenotype correlations. A recently defined myopathic genetic disease entity is caused by bi-allelic variants in a gene coding for pyridine nucleotide-disulfide oxidoreductase domain 1 (PYROXD1) with unknown substrates. Here, we present three patients from two consanguineous Turkish families with mild LGMD, facial weakness, normal CK levels, and slow progress. Genomic analyses revealed a homozygous known pathogenic missense variant (c.464A>G, p.Asn155Ser) in family 1 with two affected females. In the affected male of family 2, we found this variant in a compound heterozygous state together with a novel frameshift variant (c.329_332delTCTG, p.Leu112Valfs*8), which is the second frameshift variant known so far in PYROXD1. We have been able to define a large homozygous region in family 1 sharing a common haplotype with family 2 in the critical region. Our data suggest that c.464A>G is a Turkish founder mutation. To gain deeper insights, we performed a systematic review of all published PYROXD1-related myopathy cases. Our analysis showed that the c.464A > G variant was found in 87% (20/23) of the patients and that it may cause either a childhood- or adult-onset phenotype, irrespective of its presence in a homozygous or compound heterozygous state. Interestingly, only four patients had elevated CK levels (up to 1000 U/L), and cardiac involvement was found in few compound heterozygous cases.

On the differential diagnosis of neuropathy in neurogenetic disorders

Neuropathy might be the presenting or accompanying sign in many neurogenetic and metabolic disorders apart from the classical-peripheral neuropathies or motor-neuron diseases. This causes a diagnostic challenge which is of particular relevance since a number of the underlying diseases could be treated. Thus, we attempt to give a clinical overview on the most common genetic diseases with clinically manifesting neuropathy.

Advances in the Genetic Testing of Neuromuscular Diseases

Genetic testing in clinical practice commonly involves next-generation sequencing and most testing has been focused on specific sets of genes that are relevant to the clinical presentation (disease specific panels). Testing has typically been performed on DNA isolated from blood leukocytes. Exome sequencing is also available on for clinical testing. Some patients are particularly challenging, with negative genetic testing including (in some cases) whole exome sequencing. For some neuromuscular patients, testing of DNA or RNA isolated from muscle may provide clues that lead to the patient's diagnosis. This article presents cases to illustrate testing algorithms that may establish cases of mosaicism of the proband or parent, mitochondrial DNA mosaicism, genomic rearrangements, or novel genetic diagnoses.