A 47-year-old woman was referred to the nephrology department in February 2017, in order to initiate haemodialysis for end-stage renal disease (ESRD).
She was diagnosed with severe hypertension and chronic kidney disease (CKD) at age 20. She was born from an inbred union of a North African family and several cases of hypertension, myopia, and severe kidney disease occurred in the extended family. Her past medical history was unremarkable except for obesity. The genealogical tree (Figure 2) showed several loops of consanguinity predisposing to recessive disease. Her brother died at age 5 and one of her sisters died from stroke at age 18 due to severe hypertension. A maternal cousin, also born from an inbred union, presented with myopia, nephrotic syndrome, ESRD, requiring dialysis and renal transplantation at age 20.
At diagnosis, serum creatinine was 1.4 mg/dL. Urinary sediment was within normal limits, while a moderate mixed proteinuria was detected with a protein/creatinine ratio of 1.5 g/g. Auto-immunity screening was negative, but complement was not investigated. Renal ultrasound revealed no abnormalities. Renal magnetic resonance imaging (MRI) ruled out renal arterial stenosis, but no other tests aimed to exclude secondary hypertension were available in the patient's medical record. Angiotensin-converting enzyme inhibitor was started as the only treatment.
Five years after diagnosis, a serum creatinine of 2.79 mg/dL justified a kidney biopsy. Light microscopy (Figure 3) showed six glomeruli, five of which were within normal limits while one presented advanced sclerosis. Lesions of mild interstitial fibrosis and tubular atrophy were described. Arteries showed moderate arteriosclerosis (Figure 4). Immunofluorescence staining and electron microscopy have not been performed because frozen and glutaraldehyde fixed tissue were not available. An episode of pre-eclampsia occurred during the same year, leading to delivery at 26 weeks and post-natal death of twins.
Concurrently, an isolated cholestasis appeared. Viral serologies and immunological screening were negative. No alpha-1 anti-trypsin (AAT) deficiency was detected. Magnetic resonance imaging (MRI) showed hepatosplenomegaly and hepatic elastography values were consistent with severe fibrosis (64 kPa). Two consecutives liver biopsies showed micro-vacuolar steatosis and periportal fibrosis. Twelve years after diagnosis, because of increasing in liver enzymes and persistent severe itching, a third liver biopsy was performed. It revealed lesions of chronic cholestasis with focal acute cholangitis and peri-portal fibrosis highly suggestive of grade B biliary cirrhosis according to the Child-Pugh score.
Due to irreversible deterioration of renal function and poorly controlled hypertension, the patient started haemodialysis at 48 years of age.
A genetic work-up was performed during pre-transplant screening due to an early-onset of ESRD and liver fibrosis of unknown origin.
Clinical exome sequencing was performed on the patient's DNA using in-house SeqCap EZ choice XL capture (Roche Nimblegen, WI, USA) targeting the coding exons of 3989 genes associated with Mendelian disorders. Libraries were sequenced on an Illumina NovaSeq 6000. Variant filtering and interpretation were carried out through Highlander (https://sites.uclouvain.be/highlander/). In particular, 424 genes involved in kidney disease (i.e., cortico-resistant nephrotic syndrome/focal segmental glomerular sclerosis [FSGS], ciliopathies, etc.) were analysed (gene list available upon request). Variant classification was accomplished according to American College of Medical Genetics (ACMG) guidelines. Genetic analysis showed that the patient was homozygous for the c.626C>T (p.Pro209Leu) (P209L) variant in the TTC21B gene (NM_024753.5) (Figure 5A). The presence of this variant was validated by Sanger sequencing in the patient and her cousin who developed ESRD (Figure 5B). This variant is present with a frequency of 0.012% (34/282510 alleles) and has never been seen in the homozygous state in the gnomAD frequency database (https://gnomad.broadinstitute.org/). Several prediction tools (SIFT, MutationTaster, FATHMM, PolyPhen-2, LRT) agree with the prediction that this change is likely to be deleterious. Moreover, it has been previously reported as pathogenic in several studies. For these reasons, this variant has been classified as pathogenic (class V).
Combined liver-renal transplantation was performed at 50 of age. Basiliximab has been used as induction therapy, while methylprednisolone, tacrolimus and mofetil mycophenolate have been employed for maintenance. The immediate post-operative period was completely unremarkable. However, few months later the patient developed New Onset Diabetes After Transplantation (NODAT) and pulmonary tuberculosis that recovered without complications after treatment with isoniazid, rifampicin and ethambutol. Both liver and renal graft outcomes remained excellent 24 months after transplantation. The patient experienced substantial improvement in quality of life as she reported repeatedly during transplant follow-up.
At last follow-up, the patient's serum creatinine was 1.4 mg/dL, proteinuria was indetectable (<0.05 g/g creatinine), and urinary sediment was unremarkable. Cytolytic enzymes were within the normal limits (Alanine aminotransferase 20 U/L, Aspartate aminotransferase 26 U/L), as well as albumin (43 g/L) and prothrombin time (10.9 sec; INR 1.04).
Blood pressure was on target without any hypotensive treatment.