Intrafamilial Disease Heterogeneity in Primary Hyperoxaluria Type 1

Introduction

Primary hyperoxaluria type 1 (PH1) is known for its variable clinical course, even within families. However, the extent of this heterogeneity has not been well-studied. We aimed to analyze intrafamilial clinical heterogeneity and disease course among siblings in a large cohort of familial PH1 cases.

Methods

A retrospective registry study was performed using data from OxalEurope. All PH1 families with 2 or more affected siblings were included. A 6-point PH1 clinical outcome scoring system was developed to grade heterogeneity within a family. Intrafamilial clinical heterogeneity was defined as a score ≥2. Kaplan-Meier analyses were used to analyze differences in kidney survival between index cases and siblings.

Results

We included 88 families, encompassing 193 patients with PH1. The median interquartile range (IQR) follow-up time was 7.8 (1.9–17) years. Intrafamilial clinical heterogeneity, as defined by our score, was found in 38 (43%) PH1 families. In 54% of the families, affected siblings had a better outcome than the index case. Clinically asymptomatic siblings at the time of their diagnosis had a significantly more favorable clinical outcome based on the authors’ scoring system than siblings with clinical signs and index cases (P < 0.001). Kaplan-Meier analyses revealed that index cases reached kidney failure at an earlier age and earlier in follow-up compared to siblings (P < 0.001).

Conclusions

Intrafamilial clinical heterogeneity was found in a substantial number of familial PH1 cases. Compared to index cases, siblings had significantly better clinical outcomes and kidney survival; thereby supporting the policy of family screening to diagnose affected siblings early to improve their prognosis.