Clinical and Genetic Characteristics of Autosomal Recessive Polycystic Kidney Disease in Oman

Abstract

Background: There is a high prevalence of rare genetic disorders in the Middle East, and their study provides unique clinical and genetic insights. Autosomal recessive polycystic kidney disease (ARPKD) is one of the leading causes of kidney and liver-associated morbidity and mortality in Oman. We describe the clinical and genetic profile of cohort of ARPKD patients. Methods: We studied patients with a clinical diagnosis of ARPKD (n=40) and their relatives (parents (n=24) and unaffected siblings (n=10)) from 32 apparently unrelated families, who were referred to the National Genetic Centre in Oman between January 2015 and December 2018. Genetic analysis of PKHD1 if not previously known was performed using targeted exon PCR of known disease alleles and Sanger sequencing. Results: A clinical diagnosis of ARPKD was made prenatally in 8 patients, 21 were diagnosed during infancy (0-1 year), 9 during early childhood (2-8 years) and 2 at later ages (9-13 years). Clinical phenotypes included polycystic kidneys, hypertension, hepatic fibrosis and splenomegaly. 24 patients had documented chronic kidney disease (median age 3 years). 24 out of the 32 families had a family history suggesting an autosomal recessive pattern of inherited kidney disease, and there was known consanguinity in 21 families (66%). A molecular genetic diagnosis with biallelic PKHD1 mutations was known in 18 patients and newly identified in 20 other patients, totalling 38 patients from 30 different families. Two unrelated patients remained genetically unsolved. The different PKHD1 missense pathogenic variants were: c.107C>T, p.(Thr36Met); c.406A>G, p.(Thr136Ala); c.4870C>T, p.(Arg1624Trp) and c.9370C>T, p.(His3124Tyr) located in exons 3, 6, 32 and 58, respectively. The c.406A>G, p.(Thr136Ala) missense mutation was detected homozygously in one family and heterozygously with a c.107C>T, p.(Thr36Met) allele in 5 other families. Overall, the most commonly detected pathogenic allele was c.107C>T; (Thr36Met), which was seen in 24 families. Conclusions: Molecular genetic screening of PKHD1 in clinically suspected ARPKD cases produced a high diagnostic rate. The limited number of PKHD1 missense variants identified in ARPKD cases suggests these may be common founder alleles in the Omani population. Cost effective targeted PCR analysis of these specific alleles can be a useful diagnostic tool for future cases of suspected ARPKD in Oman.

Rare variants in PKHD1 associated with Caroli syndrome: Two case reports

“…The variant c.2702A>C has been previously reported in a large cohort of pediatric patients with autosomal recessive polycystic kidney disease (ARPKD), at compound heterozygous status (Melchionda et al, 2016) and more recently the same variant has been reported in literature as a compound heterozygote with other missense variants, in an adult patient with chronic kidney disease (CKD) of unknown etiology, who also presented a congenital hepatic fibrosis (Connaughton et al, 2019). The second variant c.4870C>T, found in the family, has been already previously detected in patients affected by ARPKD with other clinical manifestations such as developmental and speech delay, hepatomegaly, gallbladder stones, dilated segmental intrahepatic biliary radicles (Alfares et al, 2017); as this variant has been observed with high frequency in individuals living in the Middle East region, it is supposed to have a possible founder effect (Al Alawi et al, 2020).…”