Bi-allelic variants in neuronal cell adhesion molecule cause a neurodevelopmental disorder characterized by developmental delay, hypotonia, neuropathy/spasticity.

Cell adhesion molecules are membrane-bound proteins predominantly expressed in the central nervous system along principal axonal pathways with key roles in nervous system development, neural cell differentiation and migration, axonal growth and guidance, myelination, and synapse formation. Here, we describe ten affected individuals with bi-allelic variants in the neuronal cell adhesion molecule NRCAM that lead to a neurodevelopmental syndrome of varying severity; the individuals are from eight families. This syndrome is characterized by developmental delay/intellectual disability, hypotonia, peripheral neuropathy, and/or spasticity. Computational analyses of NRCAM variants, many of which cluster in the third fibronectin type III (Fn-III) domain, strongly suggest a deleterious effect on NRCAM structure and function, including possible disruption of its interactions with other proteins. These findings are corroborated by previous in vitro studies of murine Nrcam-deficient cells, revealing abnormal neurite outgrowth, synaptogenesis, and formation of nodes of Ranvier on myelinated axons. Our studies on zebrafish nrcamaΔ mutants lacking the third Fn-III domain revealed that mutant larvae displayed significantly altered swimming behavior compared to wild-type larvae (p < 0.03). Moreover, nrcamaΔ mutants displayed a trend toward increased amounts of α-tubulin fibers in the dorsal telencephalon, demonstrating an alteration in white matter tracts and projections. Taken together, our study provides evidence that NRCAM disruption causes a variable form of a neurodevelopmental disorder and broadens the knowledge on the growing role of the cell adhesion molecule family in the nervous system.

Transaldolase Deficiency: A New Case Expands the Phenotypic Spectrum.

Transaldolase (TALDO) deficiency has various clinical manifestations including liver dysfunction, hepatosplenomegaly, anemia, thrombocytopenia, and dysmorphic features. We report a case presenting prenatally with hyperechogenic bowel and intrauterine growth restriction. The infant was born small for gestational age, with cutis laxa and hypertrichosis. Postnatally, meconium plug was identified, complicated with intestinal obstruction necessitating laparotomy, partial resection of the intestine, and ileostomy. Liver biopsy revealed cholangiolar proliferation and portal fibrosis. He also suffered from persistent congenital thrombocytopenia requiring platelet transfusions and severe hypothyroidism with normal anatomical and structural gland responding only to the combination of T3 and T4 treatment. Neurologically, severe hypotonia and anisocoria were noted at the age of 2 months. Brain MRI was normal. Shortly after the abdominal surgery, a rapid liver failure ensued, which eventually led to his death. Specific metabolic tests ruled out glycosylation disorders, yet urine analysis using 1H NMR showed accumulation of sedoheptulose which was previously described in patients with transaldolase deficiency. Sequencing of the gene-encoding transaldolase (TALDO1) revealed a homozygous stop mutation c.669C>G; p.Tyr223*. In conclusion, we present an infant with a novel homozygous mutation in TALDO1, causing TALDO deficiency, and extend the clinical characteristics of this rare syndrome.