Exome Sequencing Reveals Novel Variants and Expands the Genetic Landscape for Congenital Microcephaly

Congenital microcephaly causes smaller than average head circumference relative to age, sex and ethnicity and is most usually associated with a variety of neurodevelopmental disorders. The underlying etiology is highly heterogeneous and can be either environmental or genetic. Disruption of any one of multiple biological processes, such as those underlying neurogenesis, cell cycle and division, DNA repair or transcription regulation, can result in microcephaly. This etiological heterogeneity manifests in a clinical variability and presents a major diagnostic and therapeutic challenge, leaving an unacceptably large proportion of over half of microcephaly patients without molecular diagnosis. To elucidate the clinical and genetic landscapes of congenital microcephaly, we sequenced the exomes of 191 clinically diagnosed patients with microcephaly as one of the features. We established a molecular basis for microcephaly in 71 patients (37%), and detected novel variants in five high confidence candidate genes previously unassociated with this condition. We report a large number of patients with mutations in tubulin-related genes in our cohort as well as higher incidence of pathogenic mutations in MCPH genes. Our study expands the phenotypic and genetic landscape of microcephaly, facilitating differential clinical diagnoses for disorders associated with most commonly disrupted genes in our cohort.

A Neuro-metabolic Syndrome that Needs to Be Discovered: A Child with Late Onset Asparagine Synthetase Deficiency

Asparagine synthetase (ASNS) deficiency is a rare inborn error of metabolism caused by a defect in ASNS—a gene encoding asparagine synthetase. It has mainly been described as a neurological phenotype manifesting as severe developmental delay, congenital microcephaly, spasticity, and refractory seizures; it is not associated with any specific dysmorphisms. ASNS deficiency leads to the inability to synthesize a nonessential amino acid in the brain, this explains why the symptoms are primarily neurological. The accumulation of aspartate/glutamate causes increased neuronal apoptosis leading to brain atrophy and increased neuronal excitability leading to seizures. Asparagine levels in plasma and cerebrospinal fluid are not reliable biomarkers for this disorder, therefore diagnosis is mainly obtained by molecular genetics. This disorder is associated with a poor prognosis and there is no treatment except supportive therapy. Prenatal diagnosis is possible. We report a case of a later onset form, c.146G > A (p.Arg49Gln) variant in the ASNS gene detected by molecular analysis using next-generation sequencing; the patient's clinical presentation included microcephaly, regression of developmental milestones, epilepsy, and hyperthermia.

Coordination of Zika Virus Infection and Viroplasm Organization by Microtubules and Microtubule-Organizing Centers

Zika virus (ZIKV) became a global health concern in 2016 due to its links to congenital microcephaly and other birth defects. Flaviviruses, including ZIKV, reorganize the endoplasmic reticulum (ER) to form a viroplasm, a compartment where virus particles are assembled. Microtubules (MTs) and microtubule-organizing centers (MTOCs) coordinate structural and trafficking functions in the cell, and MTs also support replication of flaviviruses. Here we investigated the roles of MTs and the cell’s MTOCs on ZIKV viroplasm organization and virus production. We show that a toroidal-shaped viroplasm forms upon ZIKV infection, and MTs are organized at the viroplasm core and surrounding the viroplasm. We show that MTs are necessary for viroplasm organization and impact infectious virus production. In addition, the centrosome and the Golgi MTOC are closely associated with the viroplasm, and the centrosome coordinates the organization of the ZIKV viroplasm toroidal structure. Surprisingly, viroplasm formation and virus production are not significantly impaired when infected cells have no centrosomes and impaired Golgi MTOC, and we show that MTs are anchored to the viroplasm surface in these cells. We propose that the viroplasm is a site of MT organization, and the MTs organized at the viroplasm are sufficient for efficient virus production.

Insights into the expanding phenotypic spectrum of inherited disorders of biogenic amines

Inherited disorders of neurotransmitter metabolism are rare neurodevelopmental diseases presenting with movement disorders and global developmental delay. This study presents the results of the first standardized deep phenotyping approach and describes the clinical and biochemical presentation at disease onset as well as diagnostic approaches of 275 patients from the registry of the International Working Group on Neurotransmitter related Disorders. The results reveal an increased rate of prematurity, a high risk for being small for gestational age and for congenital microcephaly in some disorders. Age at diagnosis and the diagnostic delay are influenced by the diagnostic methods applied and by disease-specific symptoms. The timepoint of investigation was also a significant factor: delay to diagnosis has decreased in recent years, possibly due to novel diagnostic approaches or raised awareness. Although each disorder has a specific biochemical pattern, we observed confounding exceptions to the rule. The data provide comprehensive insights into the phenotypic spectrum of neurotransmitter disorders.

A Fetus with Congenital Microcephaly, Microphthalmia and Cataract Was Detected with Biallelic Variants in the OCLN Gene: A Case Report

Microcephaly and microphthalmia are both rare congenital abnormalities, while concurrently, these two are even rarer. The underlying etiology would be complex interplaying between heterogeneous genetic background and the environmental pathogens, particularly during critical periods of early tissue development. Here, we reported a prenatal case with microcephaly, microphthalmia, and bilateral cataracts detected by ultrasonography and confirmed by autopsy. Various routine infection-related tests and invasive genetic testing were negative. Whole genome sequencing of fetus and parents revealed OCLN gene defects may be associated with these multiple congenital abnormalities.

The clinical spectrum and immunopathological mechanisms underlying ZIKV-induced neurological manifestations

Since the 2015 to 2016 outbreak in America, Zika virus (ZIKV) infected almost 900,000 patients. This international public health emergency was mainly associated with a significant increase in the number of newborns with congenital microcephaly and abnormal neurologic development, known as congenital Zika syndrome (CZS). Furthermore, Guillain–Barré syndrome (GBS), a neuroimmune disorder of adults, has also been associated with ZIKV infection. Currently, the number of ZIKV-infected patients has decreased, and most of the cases recently reported present as a mild and self-limiting febrile illness. However, based on its natural history of a typical example of reemerging pathogen and the lack of specific therapeutic options against ZIKV infection, new outbreaks can occur worldwide, demanding the attention of researchers and government authorities. Here, we discuss the clinical spectrum and immunopathological mechanisms underlying ZIKV-induced neurological manifestations. Several studies have confirmed the tropism of ZIKV for neural progenitor stem cells by demonstrating the presence of ZIKV in the central nervous system (CNS) during fetal development, eliciting a deleterious inflammatory response that compromises neurogenesis and brain formation. Of note, while the neuropathology of CZS can be due to a direct viral neuropathic effect, adults may develop neuroimmune manifestations such as GBS due to poorly understood mechanisms. Antiganglioside autoantibodies have been detected in multiple patients with ZIKV infection–associated GBS, suggesting a molecular mimicry. However, further additional immunopathological mechanisms remain to be uncovered, paving the way for new therapeutic strategies.

Placental Morphologic Similarities Between ZIKV-Positive and HIV-Positive Pregnant Women

Zika virus (ZIKV) caused global concern due to Brazil's unexpected epidemic, and it was associated with congenital microcephaly and other gestational intercurrences. The study aimed to analyze the placenta morphometric changes of ZIKV-infected pregnant women (ZIKV group; n = 23) compared to placentas of HIV-infected (HIV group; n = 24) and healthy pregnant women (N-control group; n = 22). It also analyzed the relationship between the morphometric results and pathological alterations on conventional microscopy, gestational trimester of infection, and presence of the congenital Zika syndrome (CZS). There was a significant increase in area (p = 0.0172), as well as a higher number of knots (p = 0.0027), sprouts (p < 0.0001), and CD163 +Hofbauer cells (HCs) (p < 0.0001) in the ZIKV group compared to the N-control group, suggesting that villous dysmaturity and HCs hyperplasia could be associated with ZIKV infections. The HIV group had a higher area (p < 0.0001), perimeter (p = 0.0001), sprouts (p < 0.0001), and CD163 + HCs (p < 0.0001) compared to the N-control group, demonstrating that the morphometric abnormalities found in the ZIKV and HIV group are probably similar. However, when ZIKV and HIV groups are compared, it was observed a higher number of sprouts (p = 0.0066) and CD163+ HCs (p < 0.0001) in the first one, suggesting that placental ZIKV congenital changes could be more pronounced.

Modifier Genes in Microcephaly: A Report on WDR62, CEP63, RAD50 and PCNT Variants Exacerbating Disease Caused by Biallelic Mutations of ASPM and CENPJ

Congenital microcephaly is the clinical presentation of significantly reduced head circumference at birth. It manifests as both non-syndromic—microcephaly primary hereditary (MCPH)—and syndromic forms and shows considerable inter- and intrafamilial variability. It has been hypothesized that additional genetic variants may be responsible for this variability, but data are sparse. We have conducted deep phenotyping and genotyping of five Pakistani multiplex families with either MCPH (n = 3) or Seckel syndrome (n = 2). In addition to homozygous causal variants in ASPM or CENPJ, we discovered additional heterozygous modifier variants in WDR62, CEP63, RAD50 and PCNT—genes already known to be associated with neurological disorders. MCPH patients carrying an additional heterozygous modifier variant showed more severe phenotypic features. Likewise, the phenotype of Seckel syndrome caused by a novel CENPJ variant was aggravated to microcephalic osteodysplastic primordial dwarfism type II (MOPDII) in conjunction with an additional PCNT variant. We show that the CENPJ missense variant impairs splicing and decreases protein expression. We also observed centrosome amplification errors in patient cells, which were twofold higher in MOPDII as compared to Seckel cells. Taken together, these observations advocate for consideration of additional variants in related genes for their role in modifying the expressivity of the phenotype and need to be considered in genetic counseling and risk assessment.

Further Delineation of Phenotype and Genotype of Primary Microcephaly Syndrome with Cortical Malformations Associated with Mutations in the WDR62 Gene

Type 2 congenital microcephaly (MCPH2) is a brain development disorder characterized by primary microcephaly with or without brain malformations. MCPH2 is caused by mutations in the WDR62 gene. We present three new patients with MCPH2 and compound heterozygous mutations in the WDR62 gene. In all the cases, the parents were healthy and unrelated. All children were clinically diagnosed with congenital microcephaly and retardation of motor and speech development. Sequencing results in the presented patients revealed five new variants in the WDR62 gene (c.4273C>T, c.1711_1712insTA, c.1777_1778delGA, c.1642+2T>G, c.194T>A) and one previously described in the German population (c.2864_2867delACAG). In two of the presented cases, variants in the SMAD4, DKC1, and ATRX genes were also found with unknown effects on the course of the disease. Moreover, in the article we collected and compared the most common clinical symptoms, dysmorphic features, and changes in radiographic examinations of the brain observed in 120 patients with recessive primary microcephaly type 2 caused by mutations in the WDR62 gene.

Prevalence of congenital microcephaly and its risk factors in an area at risk of Zika outbreaks

Background Prevalence of neonatal microcephaly in populations without Zika-epidemics is sparse. The study aimed to report baseline prevalence of congenital microcephaly and its relationship with prenatal factors in an area at risk of Zika outbreak. Methods This study included singletons born after 24 gestational weeks in 2017–2018 at four hospitals in Guangzhou, China. Microcephaly was defined as a head circumference at birth >3SD below the mean for sex and gestational age. Prevalence of microcephaly was estimated by binomial exact method. Multivariable logistic regression was used to examine the associations of microcephaly with prenatal factors. The population attributable fraction (PAF) for associated risk factors was calculated. Results Of 46,610 live births included, 154 (3.3, 95% CI 2.8–3.9 per 1000 live births) microcephalies were identified. Maternal hepatitis B virus carriers (HBV, OR 1.80, 95% CI 1.05–3.10) and primipara (OR 2.68, 95% CI 1.89–3.81) had higher risk of having a microcephalic baby. Higher prevalence of microcephaly was observed in women who had premature labor (OR 1.98, 95% CI 1.17–3.34) and had a baby with fetal growth restriction (OR 16.38, 95% CI 11.81–22.71). Four identified factors (HBV, primiparity, preterm labor, and fetal growth restriction) contributed to 66.4% of the risk of microcephaly. Conclusions The prevalence of microcephaly in Guangzhou was higher than expected. This study identified four prenatal risk factors that, together, contributed to two-thirds of the increased risk of microcephaly. This is the first reported association between maternal HBV carrier status and microcephaly.