Genetic blueprint of congenital muscular dystrophies with brain malformations in Egypt: A report of 11 families

Abstract

Congenital muscular dystrophies (CMDs) are a group of rare muscle disorders characterized by early onset hypotonia and motor developmental delay associated with brain malformations with or without eye anomalies in the most severe cases. In this study, we aimed to uncover the genetic basis of severe CMD in Egypt and to determine the efficacy of whole exome sequencing (WES)-based genetic diagnosis in this population. We recruited twelve individuals from eleven families with a clinical diagnosis of CMD with brain malformations that fell into two groups: seven patients with suspected dystroglycanopathy and five patients with suspected merosin-deficient CMD. WES was analyzed by variant filtering using multiple approaches including splicing and copy number variant (CNV) analysis. We identified likely pathogenic variants in FKRP in two cases and variants in POMT1, POMK, and B3GALNT2 in three individuals. All individuals with merosin-deficient CMD had truncating variants in LAMA2. Further analysis in one of the two unsolved cases showed a homozygous protein-truncating variant in Feline Leukemia Virus subgroup C Receptor 1 (FLVCR1). FLVCR1 loss of function has never been previously reported. Yet, loss of function of its paralog, FLVCR2, causes lethal hydranencephaly-hydrocephaly syndrome (Fowler Syndrome) which should be considered in the differential diagnosis for dystroglycanopathy. Overall, we reached a diagnostic rate of 86% (6/7) for dystroglycanopathies and 100% (5/5) for merosinopathy. In conclusion, our results provide further evidence that WES is an important diagnostic method in CMD in developing countries to improve the diagnostic rate, management plan, and genetic counseling for these disorders.

Dysregulation of FLVCR1a-dependent mitochondrial calcium handling in neural progenitors causes congenital hydrocephalus

“…Interestingly, variants in FLVCR1 have been recently described in additional newborns with profound hydrocephalus or microcephaly. 47 , 48 These case reports, together with the phenotype of Flvcr1a fl/fl ;NesCRE+ embryos, supported the crucial role for FLVCR1a in CH pathogenesis.…”

Unearthing FLVCR1a: tracing the path to a vital cellular transporter

“…Indeed, a homozygous protein truncating variant in FLVCR1 gene was identified in a patient with a clinical diagnosis of Walker Warburg Syndrome (WWS), a severe form of dystroglycanopathy-type congenital muscular dystrophy [ 57 ]. The patient presented with early onset hypotonia, profound hydrocephaly, myopathic changes on electromyography, contractures, seizures and optic nerve atrophy.…”