HSP60 chaperone deficiency disrupts the mitochondrial matrix proteome and dysregulates cholesterol synthesis.

OBJECTIVE: Mitochondrial proteostasis is critical for cellular function. The molecular chaperone HSP60 is essential for cell function and dysregulation of HSP60 expression has been implicated in cancer and diabetes. The few reported patients carrying HSP60 gene variants show neurodevelopmental delay and brain hypomyelination. Hsp60 interacts with more than 260 mitochondrial proteins but the mitochondrial proteins and functions affected by HSP60 deficiency are poorly characterized. METHODS: We studied two model systems for HSP60 deficiency: (1) engineered HEK cells carrying an inducible dominant negative HSP60 mutant protein, (2) zebrafish HSP60 knockout larvae. Both systems were analyzed by RNASeq, proteomics, and targeted metabolomics, and several functional assays relevant for the respective model. In addition, skin fibroblasts from patients with disease-associated HSP60 variants were analyzed by proteomics. RESULTS: We show that HSP60 deficiency leads to a differentially downregulated mitochondrial matrix proteome, transcriptional activation of stress responses, and dysregulated cholesterol biosynthesis. This leads to lipid accumulation in zebrafish knockout larvae. CONCLUSIONS: Our data provide a compendium of the effects of HSP60 deficiency on the mitochondrial matrix proteome. We show that HSP60 is a master regulator and modulator of mitochondrial functions and metabolic pathways. HSP60 dysfunction also affects cellular metabolism and disrupts the integrated stress response. The effect on cholesterol synthesis explains the effect of HSP60 dysfunction on myelination observed in patients carrying genetic variants of HSP60.

Refining the phenotype of SINO syndrome: A comprehensive cohort report of 14 novel cases.

BACKGROUND: SINO syndrome (Spastic paraplegia, Intellectual disability, Nystagmus and Obesity) is a rare autosomal dominant condition caused by heterozygous variants in KIDINS220. A total of 12 individuals are reported, comprising eight with SINO and four with an autosomal recessive condition attributed to bi-allelic KIDINS220 variants. METHODS: In our international cohort, we have comprised 14 individuals, carrying 13 novel pathogenic KIDINS220 variants in heterozygous form. We assessed clinical and molecular data of our cohort and previously reported individuals and based on functional experiments reached a better understanding of the pathogenesis behind KIDINS220-related disease. RESULTS: Using fetal tissue and in vitro assays, we demonstrate that the variants generate KIDINS220 truncated forms that mislocalize in punctate intracellular structures, with decreased levels of the full-length protein, suggesting a trans-dominant negative effect. 92% had their diagnosis within three years, with symptoms of developmental delay, spasticity, hypotonia, lack of eye contact and nystagmus. We identified a KIDINS220 variant associated with fetal hydrocephalus and show that 58% of examined individuals present brain ventricular dilatation. We extend the phenotypic spectrum of SINO syndrome to behavioral manifestations not previously highlighted. CONCLUSION: Our study provides further insights into the clinical spectrum, etiology and predicted functional impact of KIDINS220 variants.

The role of pathogenic TCF12 variants in children with coronal craniosynostosis-a systematic review with addition of two novel cases.

Craniosynostosis constitutes one of the most common congenital cranial malformations, affecting approximately 6/10,0000 live births. A genetic etiology has long been known for several forms of syndromic craniosynostosis, including pathogenic variants in TWIST1 and FGFR3 in children with Saethre-Chotzen and Muenke syndrome. Over the last decade, reports of genetic aberrations in TCF12 in children with craniosynostosis have emerged, in particular in cases with premature closure of the coronal suture(s). In this study, we, therefore, systematically reviewed the rapidly growing knowledge of TCF12-related coronal craniosynostosis, clearly illustrating its high degree of genotype and phenotype variability. With the two novel cases presented, at least 113 cases of TCF12-related coronal craniosynostosis have currently been reported. By pooling data from several prospectively collected undifferentiated craniosynostosis cohorts (ntotal = 770), we estimate a prevalence of pathogenic TCF12 variants of at least 2%. Overall, pathogenic germline variants in TCF12 are relatively frequent in children with coronal craniosynostosis, accounting for ∼10-20% of TWIST1- and FGFR1/2/3-negative cases, with even higher rates for bicoronal and syndromic cases. Genetic counseling is recommended for all children with craniosynostosis, and involvement of the coronal suture(s) should precipitate TCF12 testing.

Status epilepticus in POLG disease: a large multinational study.

We aimed to provide a detailed phenotypic description of status epilepticus (SE) in a large cohort of patients with POLG disease and identify prognostic biomarkers to improve the management of this life-threatening condition. In a multinational, retrospective study with data on patients with POLG disease from seven European countries, we identified those who had SE. The age of SE onset, accompanying clinical, laboratory, imaging and genetic findings were analysed. One hundred and ninety-five patients with genetically confirmed POLG disease were recruited, of whom 67% (130/194) had epilepsy. SE was identified in 77% (97/126), with a median age of SE onset of 7 years. SE was the presenting symptom of the disease in 43% (40/93) of those with SE, while 57% (53/93) developed SE during the disease course. Convulsive SE was reported in 97% (91/94) followed by epilepsia partialis continua in 67% (56/84). Liver impairment 78% (74/95), ataxia 69% (60/87), stroke-like episodes 57% (50/88), were the major comorbidities. In the majority (66%; 57/86) with SE this became refractory or super-refractory. The presence of seizures was associated with significantly higher mortality compared to those without (P ≤ 0.001). The median time from SE debut to death was 5 months. SE is a major clinical feature of POLG disease in early and juvenile to adult-onset disease and can be the presenting feature or arise as part of a multisystem disease. It is associated with high morbidity and mortality, with the majority of patients with SE going on to develop refractory or super-refractory SE.

Novel Alu insertion in the ZEB2 gene causing Mowat-Wilson syndrome.

Alu elements are short, interspersed elements located throughout the genome, playing a role in human diversity, and occasionally causing genetic diseases. Here, we report a novel Alu insertion causing Mowat-Wilson syndrome, a rare neurodevelopmental disorder, in an 8-year-old boy displaying the typical clinical features for Mowat-Wilson syndrome. The variant was not initially detected in genome sequencing data, but through deep phenotyping, which pointed to only one plausible candidate gene, manual inspection of genome sequencing alignment data enabled us to identify a de novo heterozygous Alu insertion in exon 8 of the ZEB2 gene. Nanopore long-read sequencing confirmed the Alu insertion, leading to the formation of a premature stop codon and likely haploinsufficiency of ZEB2. This underscores the importance of deep phenotyping and mobile element insertion analysis in uncovering genetic causes of monogenic disorders as these elements might be overlooked in standard next-generation sequencing protocols.

Variants in ZFX are associated with an X-linked neurodevelopmental disorder with recurrent facial gestalt.

Pathogenic variants in multiple genes on the X chromosome have been implicated in syndromic and non-syndromic intellectual disability disorders. ZFX on Xp22.11 encodes a transcription factor that has been linked to diverse processes including oncogenesis and development, but germline variants have not been characterized in association with disease. Here, we present clinical and molecular characterization of 18 individuals with germline ZFX variants. Exome or genome sequencing revealed 11 variants in 18 subjects (14 males and 4 females) from 16 unrelated families. Four missense variants were identified in 11 subjects, with seven truncation variants in the remaining individuals. Clinical findings included developmental delay/intellectual disability, behavioral abnormalities, hypotonia, and congenital anomalies. Overlapping and recurrent facial features were identified in all subjects, including thickening and medial broadening of eyebrows, variations in the shape of the face, external eye abnormalities, smooth and/or long philtrum, and ear abnormalities. Hyperparathyroidism was found in four families with missense variants, and enrichment of different tumor types was observed. In molecular studies, DNA-binding domain variants elicited differential expression of a small set of target genes relative to wild-type ZFX in cultured cells, suggesting a gain or loss of transcriptional activity. Additionally, a zebrafish model of ZFX loss displayed an altered behavioral phenotype, providing additional evidence for the functional significance of ZFX. Our clinical and experimental data support that variants in ZFX are associated with an X-linked intellectual disability syndrome characterized by a recurrent facial gestalt, neurocognitive and behavioral abnormalities, and an increased risk for congenital anomalies and hyperparathyroidism.