Molecular genetic studies and delineation of the oculocutaneous albinism phenotype in the Pakistani population

Abstract

BackgroundOculocutaneous albinism (OCA) is caused by a group of genetically heterogeneous inherited defects that result in the loss of pigmentation in the eyes, skin and hair. Mutations in the TYR, OCA2, TYRP1 and SLC45A2 genes have been shown to cause isolated OCA. No comprehensive analysis has been conducted to study the spectrum of OCA alleles prevailing in Pakistani albino populations.MethodsWe enrolled 40 large Pakistani families and screened them for OCA genes and a candidate gene, SLC24A5. Protein function effects were evaluated using in silico prediction algorithms and ex vivo studies in human melanocytes. The effects of splice-site mutations were determined using an exon-trapping assay.ResultsScreening of the TYR gene revealed four known (p.Arg299His, p.Pro406Leu, p.Gly419Arg, p.Arg278*) and three novel mutations (p.Pro21Leu, p.Cys35Arg, p.Tyr411His) in ten families. Ex vivo studies revealed the retention of an EGFP-tagged mutant (p.Pro21Leu, p.Cys35Arg or p.Tyr411His) tyrosinase in the endoplasmic reticulum (ER) at 37°C, but a significant fraction of p.Cys35Arg and p.Tyr411His left the ER in cells grown at a permissive temperature (31°C). Three novel (p.Asp486Tyr, p.Leu527Arg, c.1045-15 T > G) and two known mutations (p.Pro743Leu, p.Ala787Thr) of OCA2 were found in fourteen families. Exon-trapping assays with a construct containing a novel c.1045-15 T > G mutation revealed an error in splicing. No mutation in TYRP1, SLC45A2, and SLC24A5 was found in the remaining 16 families. Clinical evaluation of the families segregating either TYR or OCA2 mutations showed nystagmus, photophobia, and loss of pigmentation in the skin or hair follicles. Most of the affected individuals had grayish-blue colored eyes.ConclusionsOur results show that ten and fourteen families harbored mutations in the TYR and OCA2 genes, respectively. Our findings, along with the results of previous studies, indicate that the p.Cys35Arg, p.Arg278* and p.Gly419Arg alleles of TYR and the p.Asp486Tyr and c.1045-15 T > G alleles of OCA2 are the most common causes of OCA in Pakistani families. To the best of our knowledge, this study represents the first documentation of OCA2 alleles in the Pakistani population. A significant proportion of our cohort did not have mutations in known OCA genes. Overall, our study contributes to the development of genetic testing protocols and genetic counseling for OCA in Pakistani families.

Molecular outcomes, clinical consequences, and genetic diagnosis of Oculocutaneous Albinism in Pakistani population

“…Usually the alleles of TYR result in the retention of encoded tyrosinase in the ER1830. Here, we also observed retention of OCA2 proteins harboring missense and truncating alleles in the ER (Fig.…”

Neuropathy target esterase impairments cause Oliver–McFarlane and Laurence–Moon syndromes

“…Primers were designed using Primer3 and listed in online supplementary table S2. PCR amplification and DNA sequencing was performed as described previously 27. Mutation nomenclature was assigned in accordance with GenBank accession number NM_001166111.1 with nucleotide position 1 corresponding to the A of the ATG initiation codon.…”

Genetic Studies of TYRP1 and SLC45A2 in Pakistani Patients with Nonsyndromic Oculocutaneous Albinism

“…Identifying the genetic causes of OCA, conducting genetic testing, detecting carriers, and improving patients' understanding of the implications and consequences of the disorder through genetic counseling are essential, especially in populations that commonly practice inbreeding (Hussain and Bittles, 1998). The Pakistani population is one such example; however, genetic information regarding OCA in this population is limited (Jaworek et al, 2012). To the best of our knowledge, only one allele of OCA3 (TYRP1) and no mutations in OCA4 (SLC45A2) have been documented in the Pakistani population (Forshew et al, 2005;Jaworek et al, 2012).…”