Bi‐allelic loss of function variant in the NRCAM gene is associated with motor‐predominant axonal polyneuropathy; the second report

Background The role of biallelic variants in the NRCAM gene underlying a neurodevelopmental disorder has been defined recently. The phenotype is mainly recognized by varying severity of global developmental delay/intellectual disability, hypotonia, spasticity, and peripheral neuropathy. Methods Here, we describe a patient with an initial diagnosis of motor‐predominant axonal polyneuropathy or a form of distal SMA. Whole‐exome sequencing (WES), in parallel with WES‐based CNV detection and assessment of homozygosity runs, was performed to identify this patient's possible genetic cause. Results Whole exome sequencing revealed a homozygous variant, c.73C > T (p.Gln25*), in the NRCAM gene, while the patient manifests a mild range of phenotypes compared to NRCAM‐related disorder. He presented only motor‐predominant axonal polyneuropathy with no other signs of central nervous system involvement. Conclusions This study is the second report of an association between biallelic NRCAM gene variants and a Mendelian disorder. The obtained clinical data, together with the molecular findings in this patient, expands the clinical and molecular spectrum of NRCAM‐related disorder and highlights its phenotypic complexity. Although patients with loss of function variants in this gene have previously presented severe clinical features, we show that type of the pathogenic variant does not necessarily determine the severity of this phenotype. In this manuscript, we are describing a new patient harboring a homozygous variant in the NRCAM gene. Biallelic variants in this gene are just recently introduced as the cause of a neurodevelopmental disorder (NDD) with varying severity (Kurolap et al., March 3, 2022). To the best of our knowledge, no other affected individuals carrying NRCAM mutations have been reported later. Interestingly, our patient manifests motor‐predominant axonal polyneuropathy with no other NDD symptoms which expands the clinical and molecular spectrum of NRCAM‐related disorder.