Identification of the TTC26 Splice Variant in a Novel Complex Ciliopathy Syndrome with Biliary, Renal, Neurological, and Skeletal Manifestations

Identification of a novel QTL for lean meat percentage using imputed genotypes

Lean meat percentage is a critical production trait in pig breeding systems with direct implications for the sustainability of the industry. In this study, we conducted a genome-wide association study for lean meat percentage using a cohort of 850 Duroc × (Landrace × Yorkshire) crossbred pigs and we identified QTL on SSC3 and SSC18. Based on the predicted effect of imputed variants and using the PigGTEx database of molecular QTL, we prioritized candidate genes and SNPs located within the QTL regions, which may be involved in the regulation of porcine leanness. Our results indicate that a nonsense mutation in ZC3HAV1L on SSC18 has a direct effect on lean meat percentage.

Access and reattachment of biliary tree anomaly through Roux-en-Y hepaticojejunostomy: A case report

The right posterior segmental duct (RPSD) draining into the cystic duct is exceedingly rare. Ligation of the cystic duct in proximity to the junction of an aberrant right hepatic duct after a cholecystectomy can lead to life threatening complications. The present case study reveals a severed anomalous RPSD and subsequent Roux-en-Y hepaticojejunostomy procedure employed to fix biliary anomaly.

Mutated neuron navigator 3 as a candidate gene for a rare neurodevelopmental disorder

BACKGROUND

Neuron navigator 3 (NAV3) is characterized as one of the neuron navigator family (NAV1, NAV2, NAV3) proteins predominantly expressed in the nervous system. The NAV3-encoded protein comprises a conserved AAA and coiled-coil domains characteristic of ATPases, which are associated with different cellular activities.

METHODS

We describe a Saudi proband presenting a complex recessive neurodevelopmental disorder (NDD). Whole exome sequencing (WES) followed by Sanger sequencing, 3D protein modeling and RT-qPCR was performed.

RESULTS

WES revealed a bi-allelic frameshift variant (c.2604_2605delAG; p.Val870SerfsTer12) in exon 12 of the NAV3 gene. Furthermore, RT-qPCR revealed a significant decrease in the NAV3 mRNA expression in the patient sample, and 3D protein modeling revealed disruption of the overall secondary structure.

CONCLUSION

For the time, we associate a bi-allelic variant in the NAV3 gene causing NDD in humans.

A novel TTC26 variant in a patient with hexadactyly, pituitary stalk interruption, hepatopathy, nephropathy, and bilateral lip-palate cleft: A case report and expansion of the phenotype

Biallelic pathogenic variants in the TTC26 gene are known to cause BRENS (biliary, renal, neurological, skeletal) syndrome, an ultra-rare autosomal recessive condition with only few patients published to date. BRENS syndrome is characterized by hexadactyly, severe neonatal cholestasis, and involvement of the brain, heart, and kidney, however the full phenotypic and genotypic spectrum is unknown. Here, we report on a previously undescribed homozygous intronic TTC26 variant (c.1006-5 T > C) in a patient showing some of the known TTC26-associated features like hexadactyly, hypopituitarism, hepatopathy, nephropathy, and congenital heart defect. Moreover, he presented with a suspected unilateral hearing loss and bilateral cleft lip-palate. The variant is considered to affect correct splicing by the loss of the canonical acceptor splice site and activation of a cryptic acceptor splice site. Hereby, our patient represents one additional patient with BRENS syndrome carrying a previously unreported TTC26 variant. Furthermore, we confirm the involvement of the pituitary gland to be a common clinical feature of the syndrome and broaden the clinical spectrum of TTC26 ciliopathy to include facial clefts and a probable hearing involvement.

Caroli syndrome associated with atrial septal defect and polydactyly: a case report

INTRODUCTION

Caroli disease is multifocal segmental dilatation of the large intrahepatic bile ducts that connect to the main duct. It is considered a rare disease with an incidence rate of 1 in 1,000,000 births. There are two types of Caroli: the first type is the simple type, Caroli disease, which includes only cystic dilatation of the intrahepatic bile ducts. The second is called Caroli syndrome, which consists of Caroli disease and congenital hepatic fibrosis and might lead to portal hypertension leading to esophageal varices and splenomegaly. Atrial septal defect is one of the most common congenital heart diseases, occurring when the connection between the left and the right atriums fails to close. Polydactyly is one of the most common congenital malformations of the hands and feet. It manifests in excess fingers on the hands or toes.

CASE PRESENTATION

A 6-year-old Arab girl presented to the hospital with abdominal pain for the last month with abdominal enlargement. The patient was already diagnosed with Caroli disease and polydactyly (six fingers on each limb) when she was born. Investigations including complete blood count, blood smear, bone marrow biopsy, esophagoscopy, abdominal ultrasound, and computed tomography scan showed splenomegaly associated with hypersplenism, fourth-grade non-bleeding varices, intrahepatic cystic formations in the left and right lobes, and an atrial septal defect with a left-to-right shunt. The patient was scheduled for a splenectomy after she was vaccinated with the appropriate vaccines. After follow-up for a week in the hospital, complete blood count showed an improvement. A month after that, the patient had liver abscesses and biliary fistula that were treated appropriately and her symptoms resolved.

CONCLUSION

The association of liver diseases, polydactyly, and congenital heart diseases is extremely rare and was only documented few times in the literature. However, to our knowledge, atrial septal defect has never been part of this combination before. The family history also makes this case unique and strongly suggests genetic etiology.

Biallelic mutations of TTC12 and TTC21B were identified in Chinese patients with multisystem ciliopathy syndromes

Background

Abnormalities in cilia ultrastructure and function lead to a range of human phenotypes termed ciliopathies. Many tetratricopeptide repeat domain (TTC) family members have been reported to play critical roles in cilium organization and function.

Results

Here, we describe five unrelated family trios with multisystem ciliopathy syndromes, including situs abnormality, complex congenital heart disease, nephronophthisis or neonatal cholestasis. Through whole-exome sequencing and Sanger sequencing confirmation, we identified compound heterozygous mutations of TTC12 and TTC21B in six affected individuals of Chinese origin. These nonsynonymous mutations affected highly conserved residues and were consistently predicted to be pathogenic. Furthermore, ex vivo cDNA amplification demonstrated that homozygous c.1464 + 2 T > C of TTC12 would cause a whole exon 16 skipping. Both mRNA and protein levels of TTC12 were significantly downregulated in the cells derived from the patient carrying TTC12 mutation c.1464 + 2 T > C by real-time qPCR and immunofluorescence assays when compared with two healthy controls. Transmission electron microscopy analysis further identified ultrastructural defects of the inner dynein arms in this patient. Finally, the effect of TTC12 deficiency on cardiac LR patterning was recapitulated by employing a morpholino-mediated knockdown of ttc12 in zebrafish.

Conclusions

To the best of our knowledge, this is the first study reporting the association between TTC12 variants and ciliopathies in a Chinese population. In addition to nephronophthisis and laterality defects, our findings demonstrated that TTC21B should also be considered a candidate gene for biliary ciliopathy, such as TTC26, which further expands the phenotypic spectrum of TTC21B deficiency in humans.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40246-022-00421-z.

Novel homozygous pathogenic mitochondrial DNAJC19 variant in a patient with dilated cardiomyopathy and global developmental delay

BACKGROUND

Dilated cardiomyopathy with ataxia syndrome (DCMA) or 3-methylglutaconic aciduria type V is a rare global autosomal recessive mitochondrial syndrome that is clinically and genetically heterogeneous. It is characterized by early-onset dilated cardiomyopathy and increased urinary excretion of 3-methylglutaconic acid. As a result, some patients die due to cardiac failure, while others manifest with growth retardation, microcytic anemia, mild ataxia, and mild muscle weakness. DCMA is caused by variants in the DnaJ heat shock protein family (Hsp40) member C19 gene (DNAJC19), which plays an important role in mitochondrial protein import machinery in the inner mitochondrial membrane.

METHODS

We describe a single affected family member who presented with cardiomyopathy, global developmental delay, chest infection, seizures, elevated excretion of 3-methylglutaconic acid, and 3-methylglutaric acid in the urine.

RESULTS

Whole-exome sequencing followed by Sanger sequencing revealed a homozygous frameshift variant in the reading frame starting at codon 54 in exon 4 in the DNAJC19 gene (c.159del [Phe54Leufs*5]), which results in a stop codon four positions downstream. Quantitative gene expression analysis revealed that DNAJC19 mRNA expression in this patient was substantially reduced compared to the control.

CONCLUSIONS

We present a novel variant in the DNAJC19 gene that causes rare autosomal recessive mitochondrial 3-methylglutaconic aciduria type V. By comparing the current case with previously reported ones, we conclude that the disease is extremely heterogeneous for reasons that are still unknown.