Leen Abu Safieh

Molecular characterization of Joubert syndrome in Saudi Arabia.

Joubert syndrome (JS) is a ciliopathy that is defined primarily by typical cerebellar structural and ocular motility defects. The genetic heterogeneity of this condition is significant with 16 genes identified to date. We have used a combination of autozygome‐guided candidate gene mutation analysis and exome sequencing to identify the causative mutation in a series of 12 families. The autozygome approach identified mutations in RPGRIP1L, AHI1, TMEM237, and CEP290, while exome sequencing revealed families with truncating mutations in TCTN1 and C5ORF42. Our study, the largest comprehensive molecular series on JS, provides independent confirmation of the recently reported TCTN1, TMEM237, and C5ORF42 as bona fide JS disease genes, and expands the allelic heterogeneity of this disease. Hum Mutat 33:1423–1428, 2012.

RP1 and Retinitis Pigmentosa: Report of Novel Mutations and Insight into Mutational Mechanism

Background/aim Retinitis pigmentosa (RP) is the commonest form of retinal dystrophy and is usually inherited as a monogenic trait but with remarkable genetic heterogeneity. RP1 is one of the earliest identified disease genes in RP with mutations in this gene known to act both recessively and dominantly although the mutational mechanism remains unclear. This study is part of our ongoing effort to characterise RP in Saudi Arabia at the molecular level. Methods Homozygosity mapping and candidate gene analysis. Results The authors have identified four novel mutations, all recessive, in a number of families with a typical RP phenotype. Conclusion The distribution of these novel and previously reported RP1 mutations makes it challenging to describe a unifying mutational mechanism for dominant versus recessive RP1-related RP.

Later retinal degeneration following childhood surgical aphakia in a family with recessive CRYAB mutation (p.R56W)

Purpose: To describe later retinal degeneration following childhood cataract surgery without intraocular lens implantation in a consanguineous family with developmental cataract from homozygous p.R56W mutation in CRYAB, a gene that encodes a heat-shock protein (αB-crystallin) in both retina and the lens. Methods: Prospective ophthalmologic examination and venous blood sampling for diagnostic CRYAB sequencing in the 12 available family members (7 siblings and their 2 parents, the siblings’ maternal aunt and her son, and the siblings’ maternal grandmother). Results: Those who underwent childhood cataract surgery (2 siblings, their mother, their maternal aunt) or who had visually-insignificant lens opacities (2 siblings, their maternal grandmother) were homozygous for p.R56W CRYAB mutation. Among these 7 affected family members, clinically-obvious rod-cone degeneration was present only in the only 2 adults who were aphakic since childhood from cataract surgery. Conclusions: Recessive p.R56W CRYAB mutation shows variable expressivity for lens opacity. Decades of aphakia increases retinal light exposure and may be an environmental risk factor for significant retinal degeneration in patients homozygous for the mutation.

Methylation-Specific Multiplex-Ligation-Dependent Probe Amplification as a Rapid Molecular Diagnostic Tool for Pseudohypoparathyroidism Type 1b

Pseudohypoparathyroidism type 1b (PHP1b) is a rare metabolic bone disorder characterized by isolated renal parathyroid hormone resistance. The disorder is almost always associated with an imprinting defect or deletions in the differentially methylated region of the GNAS locus located on chromosome 20q13. In addition to the epigenetic and genetic aberrations of the differentially methylated region, PHP1b can also result from a deletion of STX16, a long-range control element of methylation at the GNAS locus located centromeric of GNAS. This report describes the utilization of a recently described methylation-specific multiplex-ligation-dependent probe amplification assay for high-throughput molecular analysis of a patient with the clinical diagnosis of PHP1b. Although more patients will need to be tested to confirm this, methylation-specific multiplex-ligation-dependent probe amplification in our hands proved to be a rapid, sensitive, and fairly easy-to-interpret assay that can be used in lieu of Southern blot analysis to diagnose PHP1b.

Autozygome maps dispensable DNA and reveals potential selective bias against nullizygosity

Purpose:Copy number variants are an important source of human genome diversity. The widespread distribution of hemizygous copy number variants in the DNA of healthy humans suggests that haploinsufficiency is largely tolerated. However, little is known about the extent to which corresponding nullizygosity (two-copy deletion) is similarly tolerated.Methods:We analyzed a cohort of first cousin unions to enrich for shared parental hemizygous events and tested their Mendelian inheritance in offspring.Results:Analysis of autozygous DNA blocks (autozygome) in the offspring not only proved an efficient method of mapping “dispensable” DNA but also revealed potential selective bias against the occurrence of nullizygous changes. This bias was not restricted to genic copy number variants and was not accounted for by a high rate of miscarriages.Conclusions:The autozygome is an efficient way to map dispensable segments of DNA and may reveal selective bias against nullizygosity in healthy individuals.Genet Med 2012:14(5):515–519

Benign reactive lymphoid hyperplasia of the conjunctiva in childhood

Background/aim Our aim is to the report the clinical and histopathological features of benign reactive lymphoid hyperplasia (BRLH) of the conjunctiva in children and the outcomes of treatment. Methods A retrospective chart review was performed for children aged 0–18 years, diagnosed with conjunctival BRLH from January 2000 to December 2013 at two large ophthalmology hospitals in the Middle East. Data were collected on patient demographics, features of the lesions, the site of the lesion, location, adnexal involvement, lymph nodes involvement, local spread, histopathology and molecular genetic studies of the cases (if available), outcomes of treatment and recurrence. Results There were 24 patients with lymphoid lesions classified as conjunctival BRLH during the 12-year period evaluated in this study. The mean age at diagnosis was 11.6 years. Twenty-three patients were males (96%). Systemic medical history included three patients with bronchial asthma, one patient with Downs syndrome, one patient with generalised skeletal malformation and one patient with gastritis. The initial uncorrected visual acuity was 20/30 or better in 93.5% of the eyes. At presentation, the tumour was unilateral in 12 cases (50%). The conjunctival mass was located on the bulbar conjunctiva in all cases. The mass was present nasally in 96% of lesions. No cases (that were tested) had an infectious aetiology. PCR demonstrated monoclonality suggestive of lymphoma in two cases; however, this did not alter the final diagnosis as BRLH per histopathological criteria and clinical course, Conclusions All investigated cases of paediatric conjunctival BRLH had a benign clinical course with no local or systemic dissemination and a male predominance. Recurrence was rare, and in our cohort, it was not associated with malignant transformation.