De novo MCM6 variants in neurodevelopmental disorders: a recognizable phenotype related to zinc binding residues

The minichromosome maintenance (MCM) complex acts as a DNA helicase during DNA replication, and thereby regulates cell cycle progression and proliferation. In addition, MCM-complex components localize to centrosomes and play an independent role in ciliogenesis. Pathogenic variants in genes coding for MCM components and other DNA replication factors have been linked to growth and developmental disorders as Meier-Gorlin syndrome and Seckel syndrome. Trio exome/genome sequencing identified the same de novo MCM6 missense variant p.(Cys158Tyr) in two unrelated individuals that presented with overlapping phenotypes consisting of intra-uterine growth retardation, short stature, congenital microcephaly, endocrine features, developmental delay and urogenital anomalies. The identified variant affects a zinc binding cysteine in the MCM6 zinc finger signature. This domain, and specifically cysteine residues, are essential for MCM-complex dimerization and the induction of helicase activity, suggesting a deleterious effect of this variant on DNA replication. Fibroblasts derived from the two affected individuals showed defects both in ciliogenesis and cell proliferation. We additionally traced three unrelated individuals with de novo MCM6 variants in the oligonucleotide binding (OB)-fold domain, presenting with variable (neuro)developmental features including autism spectrum disorder, developmental delay, and epilepsy. Taken together, our findings implicate de novo MCM6 variants in neurodevelopmental disorders. The clinical features and functional defects related to the zinc binding residue resemble those observed in syndromes related to other MCM components and DNA replication factors, while de novo OB-fold domain missense variants may be associated with more variable neurodevelopmental phenotypes. These data encourage consideration of MCM6 variants in the diagnostic arsenal of NDD.

Cranial ultrasound and MRI: complementary or not in the diagnostic assessment of children with congenital CMV infection?

Whether or not cranial ultrasound (crUS) and cerebral magnetic resonance imaging (MRI) have both a place in the assessment of children with congenital cytomegalovirus infection (cCMV) remains a topic of discussion between research groups. Literature suggests that MRI is indicated only in children with abnormal crUS.In Flanders, Belgium, combined crUS and MRI was performed on 639 children with cCMV, referred for diagnostic assessment. Cranial US was classified as abnormal in the presence of striatal vasculopathy, calcifications, cysts, cystic germinolysis, and/or ventriculomegaly. MRI findings were classified as abnormal in the presence of gyration disorders, cerebellar abnormalities, ventriculomegaly, cysts, or pathologic white matter lesions.One in five children (93/480) with normal crUS showed abnormal findings on MRI. Of them, 85 (91.4%) were classified as symptomatic. In 37 of those 93 children (39.8%), classification as severely symptomatic was made based on MRI lesions alone. MRI and crUS proved to be complementary in the assessment of CNS involvement in children with cCMV. Long-term studies are needed to evaluate the importance of this finding with respect to outcome and benefit of therapy in this particular subgroup of patients with cCMV infection.Conclusion: Our findings support an enhanced role of MRI in the diagnosis of CNS involvement in children with cCMV infection. The ideal assessment should include both imaging techniques, as the strengths of each test compensate for the other's weaknesses. What is Known: • Congenital CMV infection involves the central nervous system with direct injury to and possible disruption of brain development. • Experts suggest that MRI is indicated only in children with abnormal crUS. What is New: • In almost 20% of our children with a normal cranial ultrasound, abnormalities were detected on MRI. • Our results suggest that performing both MRI and cranial US is important to obtain a complete assessment of central nervous system involvement in children with cCMV.

Neurodevelopmental outcomes of very preterm and very-low-birthweight infants in a population-based clinical cohort with a definite perinatal treatment policy

BACKGROUND

With constant changes in neonatal care practices, recent information is valuable for healthcare providers and for parental counselling. The aim of the study was to describe the neurodevelopmental outcome in a cohort of very preterm (VPT)/very-low-birthweight (VLBW) infants at 2 years corrected age (CA).

MATERIAL AND METHODS

This is a population-based cohort study of all infants born with a GA <31 weeks and/or BW < 1500 g between 2014 and 2016 admitted to the Flemish (Belgium) neonatal intensive care units. Infants had routine clinical follow-up around 2 years CA. The diagnosis of cerebral palsy (CP), visual and hearing impairments were recorded. Motor, cognitive and language outcomes were assessed using the Bayley-III. Neurodevelopmental impairment (NDI) was classified as mild (<1 standard deviation [SD]) or moderate-severe (<2SD) based on the defined categories of motor, cognitive, hearing, and vision impairments.

RESULTS

Of the 1941 admissions, 92% survived to discharge and follow-up data were available for 1089 infants (61.1%). Overall, 19.3%, 18.9% and 41.8% of infants had a motor, cognitive and language delay, respectively. CP was diagnosed in 4.3% of the infants. Mild and moderate-to-severe NDI was observed in 25.2% and 10.9% of the infants, respectively. The number of infants with a normal outcome increased from nearly 40% in the category of GA<26 weeks to 70% for infants in the category of 30─31 weeks GA.

CONCLUSION

At 2 years CA, 64% were free from NDI and 90% were free from moderate-to-severe NDI. However, a lower GA and BW are associated with higher rates of adverse neurodevelopmental outcomes at 2 years CA.

Two novel deletions in hypotonia-cystinuria syndrome

Hypotonia-cystinuria syndrome (HCS) is an autosomal recessive disorder caused by combined deletions of SLC3A1 and PREPL. Clinical features include cystinuria, neonatal hypotonia with spontaneous improvement, poor feeding in neonates, hyperphagia in childhood, growth hormone deficiency, and variable cognitive problems. Only 14 families with 6 different deletions have been reported. Patients are often initially misdiagnosed, while correct diagnosis enables therapeutic interventions. We report two novel deletions, further characterizing the clinical and molecular genetics spectrum of HCS.