Variant in NHLRC2 leads to increased hnRNP C2 in developing neurons and the hippocampus of a mouse model of FINCA disease

Novel patients with NHLRC2 variants expand the phenotypic spectrum of FINCA disease

Purpose

FINCA disease (Fibrosis, Neurodegeneration and Cerebral Angiomatosis, OMIM 618278) is an infantile-onset neurodevelopmental and multiorgan disease. Since our initial report in 2018, additional patients have been described. FINCA is the first human disease caused by recessive variants in the highly conserved NHLRC2 gene. Our previous studies have shown that Nhlrc2-null mouse embryos die during gastrulation, indicating the essential role of the protein in embryonic development. Defect in NHLRC2 leads to cerebral neurodegeneration and severe pulmonary, hepatic and cardiac fibrosis. Despite having a structure suggestive of an enzymatic role and the clinical importance of NHLRC2 in multiple organs, the specific physiological role of the protein is unknown.

Methods

The clinical histories of five novel FINCA patients diagnosed with whole exome sequencing were reviewed. Segregation analysis of the biallelic, potentially pathogenic NHLRC2 variants was performed using Sanger sequencing. Studies on neuropathology and NHLRC2 expression in different brain regions were performed on autopsy samples of three previously described deceased FINCA patients.

Results

One patient was homozygous for the pathogenic variant c.442G > T, while the other four were compound heterozygous for this variant and two other pathogenic NHLRC2 gene variants. All five patients presented with multiorgan dysfunction with neurodevelopmental delay, recurrent infections and macrocytic anemia as key features. Interstitial lung disease was pronounced in infancy but often stabilized. Autopsy samples revealed widespread, albeit at a lower intensity than the control, NHLRC2 expression in the brain.

Conclusion

This report expands on the characteristic clinical features of FINCA disease. Presentation is typically in infancy, and although patients can live to late adulthood, the key clinical and histopathological features are fibrosis, infection susceptibility/immunodeficiency/intellectual disability, neurodevelopmental disorder/neurodegeneration and chronic anemia/cerebral angiomatosis (hence the acronym FINCA) that enable an early diagnosis confirmed by genetic investigations.

Case report: novel mutations of NDUFS6 and NHLRC2 genes potentially cause the quick postnatal death of a Chinese Hani minority neonate with mitochondrial complex I deficiency and FINCA syndrome

INTRODUCTION

Mitochondrial complex I deficiency (MCID) and abbFINCA syndrome are lethal congenital diseases and cases in the neonatal period are rarely reported. Here, we identified a Chinese Hani minority neonate with rare MCID and FINCA syndrome. This study was to analyze the clinical manifestations and pathogenic gene variations, and to investigate causes of quick postnatal death of patient and possible molecular pathogenic mechanisms.

PATIENT CONCERNS

A 17-day-old patient had reduced muscle tension, diminished primitive reflexes, significantly abnormal blood gas analysis, and progressively increased blood lactate and blood glucose. Imaging studies revealed pneumonia, pulmonary hypertension, and brain abnormalities.

DIAGNOSIS

Whole-exome sequencing revealed that the NDUFS6 gene of the patient carried c. 344G > T (p.C115F) novel homozygous variation, and the NHLRC2 gene carried c. 1749C > G (p.F583L) and c. 2129C > T (p.T710M) novel compound heterozygous variation.

INTERVENTIONS AND OUTCOMES

The patient was given endotracheal intubation, respiratory support, high-frequency ventilation, antishock therapy, as well as iNO and Alprostadil to reduce pulmonary hypertension and maintain homeostatic equilibrium. However, the patient was critically ill and died in 27 days.

CONCLUSION

The patient has MCID due to a novel mutation in NDUFS6 and FINCA syndrome due to novel mutations in NHLRC2, which is the main reason for the rapid onset and quick death of the patient.

Nhlrc2 is crucial during mouse gastrulation

The loss of NHL repeat containing 2 (Nhlrc2) leads to early embryonic lethality in mice, but the exact timing is currently unknown. In this study, we determined the time of lethality for Nhlrc2 knockout (KO), C57BL/6NCrl‐Nhlrc2^{tm1a(KOMP)Wtsi}/Oulu, embryos and the in situ expression pattern of Nhlrc2 based on LacZ reporter gene expression during this period. Nhlrc2 KO preimplantation mouse embryos developed normally after in vitro fertilization. Embryonic stem (ES) cells established from KO blastocysts proliferated normally despite a complete loss of the NHLRC2 protein. Nhlrc2 KO embryos from timed matings implanted and were indistinguishable from their wildtype littermates on embryonic day (E) 6.5. On E7.5, Nhlrc2 KO embryo development was arrested, and on E8.5, only 6% of the genotyped embryos were homozygous for the Nhlrc2^{tm1a(KOMP)Wtsi} allele. Nhlrc2 KO E8.5 embryos showed limited embryonic or extraembryonic tissue differentiation and remained at the cylinder stage. Nhlrc2 expression was ubiquitous but strongest in the epiblast/ectoderm and extraembryonic ectoderm on E6.5 and E7.5. NHLRC2 is essential for early postimplantation development, and its loss leads to failed gastrulation and amniotic folding in mice. Future studies on the evolutionarily conserved NHLRC2 will provide new insights into the molecular pathways involved in the early steps of postimplantation development.

Expanding the phenotypic spectrum of FINCA (fibrosis, neurodegeneration, and cerebral angiomatosis) syndrome beyond infancy

Fibrosis, neurodegeneration, and cerebral angiomatosis (FINCA, MIM#618278) is a rare clinical condition caused by bi-allelic variants in NHL repeat containing protein 2 (NHLRC2, MIM*618277). Pulmonary disease may be the presenting sign and the few patients reported so far, all deceased in early infancy. Exome sequencing was performed on patients with childhood interstitial lung disease (chILD) and additional neurological features. The chILD-EU register database and an in-house database were searched for patients with NHLRC2 variants and clinical features overlapping FINCA syndrome. Six patients from three families were identified with bi-allelic variants in NHLRC2. Two of these children died before the age of two while four others survived until childhood. Interstitial lung disease was pronounced in almost all patients during infancy and stabilized over the course of the disease with neurodevelopmental delay (NDD) evolving as the key clinical finding. We expand the phenotype of FINCA syndrome to a multisystem disorder with variable severity. FINCA syndrome should also be considered in patients beyond infancy with NDD and a history of distinct interstitial lung disease. Managing patients in registers for rare diseases helps identifying new diagnostic entities and advancing care for these patients.