MFSD2A-associated primary microcephaly - Expanding the clinical and mutational spectrum of this ultra-rare disease.

MFSD2A, a member of the major facilitator superfamily (MFS), is a transmembrane transporter responsible for the uptake of specific essential fatty acids through the blood-brain barrier (BBB) to the brain. The transporter is crucial for early embryonic brain development and a major factor in the formation and maintenance of the BBB. Mfsd2a-knockout mice show a leakage of the BBB in early embryonic stages and develop a phenotype characterized by microcephaly, cognitive impairment, and anxiety. So far, homozygous or compound heterozygous MFSD2A mutations in humans have only been reported in 13 different families with a total of 28 affected individuals. The phenotypical spectrum of patients with MFSD2A variants is rather broad but all patients present with microcephaly and severe intellectual disability, absent or limited speech, and walking difficulties. Severely affected patients develop seizures and show brain malformations and have, above all, a profound developmental delay hardly reaching any developmental motor milestones. Here, we report on two unrelated individuals with novel homozygous variants in the MFSD2A gene, presenting with severe primary microcephaly, brain malformations, profound developmental delay, and epilepsy, including hypsarrhythmia. Our findings extend the mutational spectrum of the bi-allelic MFSD2A variants causing autosomal recessive primary microcephaly type 15 and broaden the phenotypic spectrum associated with these pathogenic variants emphasizing the role of MFSD2A in early brain development.

Clinical relevance of postzygotic mosaicism in Cornelia de Lange syndrome and purifying selection of NIPBL variants in blood.

Postzygotic mosaicism (PZM) in NIPBL is a strong source of causality for Cornelia de Lange syndrome (CdLS) that can have major clinical implications. Here, we further delineate the role of somatic mosaicism in CdLS by describing a series of 11 unreported patients with mosaic disease-causing variants in NIPBL and performing a retrospective cohort study from a Spanish CdLS diagnostic center. By reviewing the literature and combining our findings with previously published data, we demonstrate a negative selection against somatic deleterious NIPBL variants in blood. Furthermore, the analysis of all reported cases indicates an unusual high prevalence of mosaicism in CdLS, occurring in 13.1% of patients with a positive molecular diagnosis. It is worth noting that most of the affected individuals with mosaicism have a clinical phenotype at least as severe as those with constitutive pathogenic variants. However, the type of genetic change does not vary between germline and somatic events and, even in the presence of mosaicism, missense substitutions are located preferentially within the HEAT repeat domain of NIPBL. In conclusion, the high prevalence of mosaicism in CdLS as well as the disparity in tissue distribution provide a novel orientation for the clinical management and genetic counselling of families.

Genetic analysis of VCP and WASH complex genes in a German cohort of sporadic ALS-FTD patients.

Mutations of the human valosin-containing protein, p97 (VCP) and Wiskott-Aldrich syndrome protein and SCAR homolog (WASH) complex genes cause motor neuron and cognitive impairment disorders. Here, we analyzed a cohort of German patients with sporadic amyotrophic lateral sclerosis and frontotemporal lobar degeneration comorbidity (ALS/FTD) for VCP and WASH complex gene mutations. Next-generation panel sequencing of VCP, WASH1, FAM21C, CCDC53, SWIP, strumpellin, F-actin capping protein of muscle Z-line alfa 1 (CAPZA1), and CAPZB genes was performed in 43 sporadic ALS/FTD patients. Subsequent analyses included Sanger sequencing, in silico analyses, real-time PCR, and CCDC53 immunoblotting. We identified 1 patient with the heterozygous variant c.26C>T in CAPZA1, predicted to result in p.Ser9Leu, and a second with the heterozygous start codon variant c.2T>C in CCDC53. In silico analysis predicted structural changes in the N-terminus of CAPZα1, which may interfere with CAPZα:CAPZß dimerization. Though the translation initiation codon of CCDC53 is mutated, real-time PCR and immunoblotting did neither reveal any evidence for a CCDC53 haploinsufficiency nor for aberrant CCDC53 protein species. Moreover, a disease-causing C9orf72 repeat expansion mutation was later on identified in this patient. Thus, with the exception of a putatively pathogenic heterozygous c.26C>T CAPZA1 variant, our genetic analysis did not reveal mutations in VCP and the remaining WASH complex subunits.