Oculocutaneous albinism and bleeding diathesis due to a novel deletion in the HPS3 gene

Abstract

Hermansky-Pudlak syndrome (HPS) is a group of rare autosomal recessive disorders characterized by oculocutaneous albinism (OCA) and bleeding diathesis. To date, 11 HPS types have been reported (HPS-1 to HPS-11), each defined by disease-causing variants in specific genes. Variants in the HPS1 gene were found in approximately 15% of HPS patients, most of whom harbor the Puerto Rican founder mutation. In this study, we report six affected individuals from three nonconsanguineous families of Ashkenazi Jewish descent, who presented with OCA and multiple ecchymoses and had normal platelet number and size. Linkage analysis indicated complete segregation to HPS3. Sequencing of the whole coding region and the intron boundaries of HPS3 revealed a heterozygous c.1163+1G>A variant in all six patients. Long-range PCR amplification revealed that all affected individuals also carry a 14,761bp deletion that includes the 5'UTR and exon 1 of HPS3, encompassing regions with long interspersed nuclear elements. The frequency of the c.1163+1G>A splice site variant was found to be 1:200 in the Ashkenazi Jewish population, whereas the large deletion was not detected in 300 Ashkenazi Jewish controls. These results present a novel HPS3 deletion mutation and suggest that the prevalence of HPS-3 in Ashkenazi Jews is more common than previously thought.

Keywords: Ashkenazi Jewish; HPS-3; HPS3; Hermansky–Pudlak syndrome; deletion; oculocutaneous albinism.

FIGURE 1

Clinical manifestations of Hermansky–Pudlak syndrome (HPS)-3 patients. HPS-3 patients have variable hypopigmentation of skin and hair, as shown in probands 4 and 5 (B-II:8 and B-II:9, respectively) (A–B), and some show multiple ecchymoses due to a bleeding diathesis in HPS patients (proband 5) (C).

FIGURE 2

Pedigrees and Haplotype analysis of the six probands’ families. Pedigrees include genotyping results shown as wild type (w.t.), large deletion (Ldel) or splice site mutation (+1G>A), and the inherited chromosomes; each allele illustrated with different patterns. Five polymorphic markers from clones located very close and on both sides of the HPS3 gene were used. From top to bottom: AC092979, AC021059059 (5′-upstream of the HPS3 gene), AC131209 (Intra genic-IG), AC093001, AC073522 (3′-downstream of the gene). Arrows pint to the affected member in each family.

FIGURE 3

Identification of a large deletion in HPS3. (A) Top: Scheme of the HPS3 deletion and multiplex PCR amplification assay with three primers: delF and delR across the deletion and inR within the deletion. Chromatogram of the deletion breakpoint sequence. Bottom: Schematic basis of the deleted allele, which shows deletion of the 5′ UTR and exon 1. The deletion occurs between two LINE-1 repeats (black box). (B) Multiplex PCR amplification yield a lower 300 bp band (del1F + delR) and upper 450 bp band (delF + inR) for the normal and mutant allele, respectively. Asterisk denotes nonspecific bands (faint band ∼600 bp). M, marker (100 kb ladder); bp, base pairs.

FIGURE 4

Molecular analysis of the compound heterozygous probands. (A) HPS3 mRNA expression in fibroblasts from four different WT controls, Hermansky–Pudlak syndrome (HPS)-1 (patient with biallelic mutations in HPS1), HPS-3 (patient with biallelic mutations in HPS3), and HPS-5 (patient with biallelic mutations in HPS5). Proband 3 is B-II:5 and with HPS-3 disorder. HPS3 mRNA expression is reduced in patients with biallelic mutations in HPS3 as compared with control. (B) Western blotting from the mentioned above samples probing for HPS-5 aiming to evaluate BLOC-2 stability; β (beta) Actin was used as a control to normalize results. (C) Western blotting quantification of B, showing that HPS-5 protein is decreased in HPS-3 patient, proband II:5) to approximately 40% compared with WT.