# First LDLRAP1 and Recurrent LDLR Mutations in Tunisian Families With Familial Hypercholesterolemia

## TL;DR

This study reports the first cases of autosomal recessive familial hypercholesterolemia in Tunisia, caused by mutations in the LDLRAP1 gene, and highlights the genetic diversity of the condition.

## Contribution

The first identification of LDLRAP1 mutations in Tunisian families with autosomal recessive familial hypercholesterolemia.

## Key findings

- A novel homozygous LDLRAP1 missense variant (p.Gly54Asp) was found to cause autosomal recessive FH in one family.
- A recurrent LDLR splice-site variant was identified in another family, following an autosomal dominant inheritance pattern.
- The LDLRAP1 variant was predicted to destabilize the PTB domain, likely impairing LDL receptor internalization.

## Abstract

Familial hypercholesterolemia (FH) is a genetic disorder characterised by elevated plasma LDL‐cholesterol, predisposing to premature atherosclerotic cardiovascular disease. Most cases follow an autosomal dominant pattern (ADH) caused by pathogenic variants in LDLR, APOB or PCSK9. In contrast, the rare autosomal recessive form (ARH) results from biallelic mutations in LDLRAP1, leading to defective LDL receptor‐mediated endocytosis. Despite the high rate of consanguinity in Tunisia, LDLRAP1 variants have not yet been reported in this population. In this study, Whole Exome Sequencing of two consanguineous Tunisian families, identified distinct pathogenic variants. In the first family (FH‐A), a recurrent LDLR splice‐site variant (c.1845+1G>A) was detected in both heterozygous and homozygous states, consistent with an autosomal dominant inheritance pattern. In the second family (FH‐B), a novel homozygous LDLRAP1 missense variant (c.161G>A; p.Gly54Asp) was identified, confirming autosomal recessive inheritance. In silico analyses using MutationTaster, DynaMut2, MUpro, DDGun, NetSurfP‐2.0, ConSurf and PyMOL predicted that the p.Gly54Asp substitution destabilises the PTB domain of LDLRAP1 by disrupting key hydrogen bonds and hydrophobic interactions, thereby likely impairing LDLR internalisation. According to ACMG guidelines, this variant is classified as likely pathogenic. Clinically, ARH patients exhibited early‐onset xanthomas and an unusual quadricuspid aortic valve (QAV). Targeted analysis of valvulogenesis genes (NOTCH1, GATA4, NKX2‐5, TBX5, AGTR1, BMP2) revealed no co‐segregating pathogenic variants, suggesting that QAV may result from embryonic LDL accumulation disrupting Notch1 signalling rather than a monogenic defect. Comparison with other ADH Tunisian families carrying the same LDLR mutation showed phenotypic variability, likely influenced by genetic modifiers, treatment response and environmental factors. These findings provide the first evidence of LDLRAP1‐associated ARH in Tunisia and highlight the genetic heterogeneity of FH, emphasising the importance of integrating molecular, structural and functional analyses for accurate diagnosis, personalised management and early prevention.