Dominant monoallelic variant in the PAK2 gene causes Knobloch syndrome type 2

Phenotypic Expansion of Knobloch Syndrome Type 2 in an Individual With a De Novo PAK2 Variant

P21-activated kinase 2 (PAK2) is a serine/threonine kinase essential for a variety of cellular processes including signal transduction, cellular survival, proliferation, and migration. A recent report proposed monoallelic PAK2 variants cause Knobloch syndrome type 2 (KNO2)-a developmental disorder primarily characterized by ocular anomalies. Here, we identified a novel de novo heterozygous missense variant in PAK2, NM_002577.4:c.1273G>A, p.(D425N), by genome sequencing in an individual with features consistent with KNO2. Notable clinical phenotypes observed in this individual were global developmental delay, congenital retinal detachment, mild cerebral ventriculomegaly, hypotonia, failure to thrive, pyloric stenosis, feeding intolerance, patent ductus arteriosus, and mild facial dysmorphism. The p.(D425N) variant lies within the protein kinase domain and is predicted to be functionally damaging by in silico analysis. Previous clinical genetic testing did not report this variant due to unknown relevance of PAK2 variants at the time of testing, highlighting the importance of reanalysis. Our findings substantiate the candidacy of PAK2 variants in KNO2 and expand the KNO2 clinical phenotypic spectrum.

Retinal detachment in a neonate with congenital chylothorax and purpura fulminans associated with the PAK2 genetic variant: A case report

INTRODUCTION AND IMPORTANCE

A potential relationship between bilateral retinal detachment, chylothorax, and purpura fulminans in a female neonate with a PAK2 gene variant is not commonly reported. This emphasizes the significance of early ophthalmologic assessment in neonates with congenital chylothorax.

CASE PRESENTATION

A full-term female infant weighing 2.775 kg was delivered by cesarean section due to breech presentation. Prenatal imaging revealed fetal bilateral pleural effusion, suggestive of chylothorax. The neonate developed respiratory distress and purpura fulminans after birth. The absence of the red reflex in the right eye prompted a detailed ophthalmologic examination using a portable slit lamp and an indirect ophthalmoscope. The right eye revealed an ectatic pupil with posterior synechia extending from approximately 6 o'clock to 9 o'clock. Fundus examination of both eyes revealed funnel retinal detachment with multiple chronic features. A small amount of retina was draped between 4 and 7 o'clock, which may have been attached. Further ophthalmologic investigation under anesthesia, using B-scan ultrasonography and intravenous fluorescein angiography, confirmed bilateral retinal detachment. Genetic investigations revealed a PAK2 c.1115A>T, p.(Asp372Val) variant.

CLINICAL DISCUSSION

In addition to presenting our case report, we reviewed other recent case reports similar to ours. Retinal detachment and bilateral pleural effusions in neonates with Knobloch syndrome have been recently reported, but without purpura fulminans. Retinal detachment in neonates can result from both congenital and acquired conditions, and requires a thoughtful approach to establish the diagnosis and provide future counseling.

CONCLUSION

Bilateral retinal detachment, chylothorax, and purpura fulminans in a neonate with a PAK2 genetic variant is uncommon. This case underscores the importance of early ophthalmologic assessment and genetic testing for both neonates and their family members.

Hereditary Vitreoretinopathies: Molecular Diagnosis, Clinical Presentation and Management

Hereditary vitreoretinopathies (HVRs), also known as hereditary vitreoretinal degenerations comprise a heterogeneous group of inherited disorders of the retina and vitreous, collectively and variably characterised by vitreal abnormalities, such as fibrillary condensations, liquefaction or membranes, as well as peripheral retinal abnormalities, vascular changes in some, an increased risk of retinal detachment and early-onset cataract formation. The pathology often involves the vitreoretinal interface in some, while the major underlying abnormality is vascular in others. Recent advances in molecular diagnosis and identification of the responsible genes and have improved our understanding of the pathogenesis, risks and management of the HVRs. Clinically, HVRs can be classified according to the presence or absence of skeletal or other systemic abnormalities, retinal dysfunction or retinal vascular abnormalities [2]. There are some discrepancies in the literature regarding which diseases are included under the overarching term 'hereditary vitreoretinopathies'. Conditions such as Stickler syndrome, Wagner syndrome and familial exudative vitreoretinopathy are generally included, while others such as autosomal dominant neovascular inflammatory vitreoretinopathy (ADNIV) and autosomal dominant vitreoretinochoroidapathy (ADVIRC) may not. In this review, we will discuss some historical aspects, the molecular pathogenesis, clinical features and management of diseases and syndromes commonly considered as HVRs.

Chinese Family With Knobloch Syndrome Associated With a Novel PAK2 Variant Leading to Reduced Phosphorylation Levels

BACKGROUND

Biallelic variants of COL18A1 cause Knobloch syndrome (KNO), a rare genetic disorder, characterized by oculopathy and structural defects. Recently, several studies have suggested that novel de novo missense variants in PAK2 may be associated with KNO; however, there are few case reports. This study aimed to investigate a patient with KNO who initially presented with seizures and expand the PAK2 genotype and phenotype spectrum.

METHODS

This study included a Chinese family with a proband who primarily presented with epilepsy and developmental delay. Whole-exome sequencing and Sanger sequencing were performed to analyze potential variants. Structural modeling was performed to assess the impact of the variant on the protein structure. In vitro, a mutant plasmid was constructed and transfected into 293T cells to conduct phosphorylation assays, and phosphorylation levels at Ser141 of PAK2 were assessed. The PAK kinase inhibitor FRAX597 was used to confirm the specificity of the western blot results.

RESULTS

A de novo variant of PAK2 gene, NM_002577.4: c.1049G>A (p.Arg350Lys) was found in the patient but not in his parents or sister. This variant was found to be located in the kinase domain and may alter the hydrogen-bond network, potentially affecting kinase activity. In vitro functional experiments demonstrated that the variant may lead to reduced protein levels. Moreover, Western blot analysis showed a significant decrease in the phosphorylation level at Ser141 compared to the wild-type plasmid, indicating that the variant may lead to decreased PAK2 phosphorylation levels.

CONCLUSION

The clinical manifestations in this patient may be associated with a novel PAK2 variant, and the atypical presentation of KNO suggests that PAK2-related KNO may have a broader phenotypic spectrum.

Antenatal phenotype associated with PAK2 pathogenic variants: bilateral pleural effusion as a warning sign

Fetal pleural effusions can arise in various contexts with different prognosis. They have been reported in fetuses presenting with hereditary or acquired conditions. One particularly rare genetic disorder, known as Knobloch syndrome, seems to emerge as a potential new cause of fetal pleural effusions, associated with severe outcomes. Knobloch syndrome 1 can be caused by biallelic variants in COL18A1. It is primarily characterized by its ophthalmic features, including severe vitreoretinal degeneration with retinal detachment and macular abnormalities. Neurological defects such as encephalocele and developmental delay, along with skeletal and renal malformations, are also associated with the syndrome. The Knobloch syndrome 2 is caused by monoallelic variants in the kinase domain of PAK2. It is less described and seems to also be associated with cardiac and respiratory damage in addition to the Knobloch syndrome 1 phenotype. PAK2 is a ubiquitous protein with a major implication in regulation and remodeling of the cytoskeleton and numerous other cellular pathways. Knobloch-associated variants seem to cause a loss of the kinase function of the protein. Even if the ophthalmic defects are almost constant, PAK2-associated Knobloch syndrome has slightly different features from Knobloch syndrome 1 in which pulmonary and lymphatic damages are still unseen. In a prenatal trio exome sequencing, we identified a novel de novo PAK2 missense variant, NM_002577.4:c.836 A > C, p.(Gln279Pro), classified as likely pathogenic in a 24 weeks of gestation fetus whose only sign was severe bilateral pleural effusion. From a literature review of patients, we recognize this sign as an important antenatal indicator of Knobloch syndrome 2, as it was the first sign identifiable in 2 out of 5 patients. This adds new evidence for the implication of this gene in fetal pleural effusions, with potentially severe outcomes.

New kinase-deficient PAK2 variants associated with Knobloch syndrome type 2

The p21-activated kinase (PAK) family of proteins regulates various processes requiring dynamic cytoskeleton organization such as cell adhesion, migration, proliferation, and apoptosis. Among the six members of the protein family, PAK2 is specifically involved in apoptosis, angiogenesis, or the development of endothelial cells. We report a novel de novo heterozygous missense PAK2 variant, p.(Thr406Met), found in a newborn with clinical manifestations of Knobloch syndrome. In vitro experiments indicated that this and another reported variant, p.(Asp425Asn), result in substantially impaired protein kinase activity. Similar findings were described previously for the PAK2 p.(Glu435Lys) variant found in two siblings with proposed Knobloch syndrome type 2 (KNO2). These new variants support the association of PAK2 kinase deficiency with a second, autosomal dominant form of Knobloch syndrome: KNO2.

3q29 duplications: A cohort of 46 patients and a literature review

Duplications of the 3q29 cytoband are rare chromosomal copy number variations (CNVs) (overlapping or recurrent ~1.6 Mb 3q29 duplications). They have been associated with highly variable neurodevelopmental disorders (NDDs) with various associated features or reported as a susceptibility factor to the development of learning disabilities and neuropsychiatric disorders. The smallest region of overlap and the phenotype of 3q29 duplications remain uncertain. We here report a French cohort of 31 families with a 3q29 duplication identified by chromosomal microarray analysis (CMA), including 14 recurrent 1.6 Mb duplications, eight overlapping duplications (>1 Mb), and nine small duplications (<1 Mb). Additional genetic findings that may be involved in the phenotype were identified in 11 patients. Focusing on apparently isolated 3q29 duplications, patients present mainly mild NDD as suggested by a high rate of learning disabilities in contrast to a low proportion of patients with intellectual disabilities. Although some are de novo, most of the 3q29 duplications are inherited from a parent with a similar mild phenotype. Besides, the study of small 3q29 duplications does not provide evidence for any critical region. Our data suggest that the overlapping and recurrent 3q29 duplications seem to lead to mild NDD and that a severe or syndromic clinical presentation should warrant further genetic analyses.

A de novo variant in PAK2 detected in an individual with Knobloch type 2 syndrome

P21-activated kinase 2 (PAK2) is a serine/threonine kinase essential for a variety of cellular processes including signal transduction, cellular survival, proliferation, and migration. A recent report proposed monoallelic PAK2 variants cause Knobloch syndrome type 2 (KNO2)-a developmental disorder primarily characterized by ocular anomalies. Here, we identified a novel de novo heterozygous missense variant in PAK2, NM_002577.4:c.1273G>A, p.(D425N), by whole genome sequencing in an individual with features consistent with KNO2. Notable clinical phenotypes include global developmental delay, congenital retinal detachment, mild cerebral ventriculomegaly, hypotonia, FTT, pyloric stenosis, feeding intolerance, patent ductus arteriosus, and mild facial dysmorphism. The p.(D425N) variant lies within the protein kinase domain and is predicted to be functionally damaging by in silico analysis. Previous clinical genetic testing did not report this variant due to unknown relevance of PAK2 variants at the time of testing, highlighting the importance of reanalysis. Our findings also substantiate the candidacy of PAK2 variants in KNO2 and expand the KNO2 clinical spectrum.

Whole exome sequencing and polygenic assessment of a Swedish cohort with severe developmental language disorder

Developmental language disorder (DLD) overlaps clinically, genetically, and pathologically with other neurodevelopmental disorders (NDD), corroborating the concept of the NDD continuum. There is a lack of studies to understand the whole genetic spectrum in individuals with DLD. Previously, we recruited 61 probands with severe DLD from 59 families and examined 59 of them and their families using microarray genotyping with a 6.8% diagnostic yield. Herein, we investigated 53 of those probands using whole exome sequencing (WES). Additionally, we used polygenic risk scores (PRS) to understand the within family enrichment of neurodevelopmental difficulties and examine the associations between the results of language-related tests in the probands and language-related PRS. We identified clinically significant variants in four probands, resulting in a 7.5% (4/53) molecular diagnostic yield. Those variants were in PAK2, MED13, PLCB4, and TNRC6B. We also prioritized additional variants for future studies for their role in DLD, including high-impact variants in PARD3 and DIP2C. PRS did not explain the aggregation of neurodevelopmental difficulties in these families. We did not detect significant associations between the language-related tests and language-related PRS. Our results support using WES as the first-tier genetic test for DLD as it can identify monogenic DLD forms. Large-scale sequencing studies for DLD are needed to identify new genes and investigate the polygenic contribution to the condition.

Knobloch syndrome - a rare collagenopathy, revealing peripheral avascular retina

INTRODUCTION

Pediatric rhegmatogenous retinal detachments, especially those presenting at birth or soon afterward, have a high likelihood of syndromic associations that can be confirmed by genetic testing.

MATERIALS AND METHODS

A 5-month-old child was found to have high myopia in the right eye (RE) with highly tessellated fundus, opalescent vitreous, and peripheral thinning. Left eye had a shallow retinal detachment for which he underwent belt buckling. The baby had an occipital skin tag. A provisional diagnosis of Stickler syndrome was made.

RESULTS

On 1-month follow-up, left eye retina was attached and 360° laser barrage was done. Fluorescein angiography was done which revealed peripheral avascular retina in both eyes. MRI and genetic testing were suggestive of syndromic association. Genetic testing revealed pathogenic mutation in COL 18A1 suggestive of Knobloch syndrome in the baby, and both parents were found to be carriers of the same mutation. However, brain MRI showed features not pathognomonic of Knobloch syndrome.

CONCLUSION

Although Knobloch syndrome is associated with vitreoretinal degeneration and high risk of retinal detachment, there seems to be no recommendation for prophylaxis in the other eye and therefore we preferred to observe the RE closely. A unique feature noted in our case was the peripheral avascular zone (PAZ). The PAZ could be contributed by multiple factors such as high myopia, or due to endostatin deficiency (which is a derivative of collagen XVIII) or an underlying WNT signalling abnormality.

The molecular basis of p21-activated kinase-associated neurodevelopmental disorders: From genotype to phenotype

Although the identification of numerous genes involved in neurodevelopmental disorders (NDDs) has reshaped our understanding of their etiology, there are still major obstacles in the way of developing therapeutic solutions for intellectual disability (ID) and other NDDs. These include extensive clinical and genetic heterogeneity, rarity of recurrent pathogenic variants, and comorbidity with other psychiatric traits. Moreover, a large intragenic mutational landscape is at play in some NDDs, leading to a broad range of clinical symptoms. Such diversity of symptoms is due to the different effects DNA variations have on protein functions and their impacts on downstream biological processes. The type of functional alterations, such as loss or gain of function, and interference with signaling pathways, has yet to be correlated with clinical symptoms for most genes. This review aims at discussing our current understanding of how the molecular changes of group I p21-activated kinases (PAK1, 2 and 3), which are essential actors of brain development and function; contribute to a broad clinical spectrum of NDDs. Identifying differences in PAK structure, regulation and spatio-temporal expression may help understanding the specific functions of each group I PAK. Deciphering how each variation type affects these parameters will help uncover the mechanisms underlying mutation pathogenicity. This is a prerequisite for the development of personalized therapeutic approaches.