Exome sequencing and cis-regulatory mapping identify mutations in MAK, a gene encoding a regulator of ciliary length, as a cause of retinitis pigmentosa.

A fundamental challenge in analyzing exome-sequence data is distinguishing pathogenic mutations from background polymorphisms. To address this problem in the context of a genetically heterogeneous disease, retinitis pigmentosa (RP), we devised a candidate-gene prioritization strategy called cis-regulatory mapping that utilizes ChIP-seq data for the photoreceptor transcription factor CRX to rank candidate genes. Exome sequencing combined with this approach identified a homozygous nonsense mutation in male germ cell-associated kinase (MAK) in the single affected member of a consanguineous Turkish family with RP. MAK encodes a cilium-associated mitogen-activated protein kinase whose function is conserved from the ciliated alga, Chlamydomonas reinhardtii, to humans. Mutations in MAK orthologs in mice and other model organisms result in abnormally long cilia and, in mice, rapid photoreceptor degeneration. Subsequent sequence analyses of additional individuals with RP identified five probands with missense mutations in MAK. Two of these mutations alter amino acids that are conserved in all known kinases, and an in vitro kinase assay indicates that these mutations result in a loss of kinase activity. Thus, kinase activity appears to be critical for MAK function in humans. This study highlights a previously underappreciated role for CRX as a direct transcriptional regulator of ciliary genes in photoreceptors. In addition, it demonstrates the effectiveness of CRX-based cis-regulatory mapping in prioritizing candidate genes from exome data and suggests that this strategy should be generally applicable to a range of retinal diseases.

Sapropterin dihydrochloride treatment in Turkish hyperphenylalaninemic patients under age four.

Sapropterin enhances phenylalanine hydroxylase activity, thus lowering blood phenylalanine (Phe) concentration while increasing protein tolerance in sapropterin-responsive patients. Initiation of sapropterin treatment in responsive patients as early as possible, especially during the time when brain development is fastest, allows intake of more natural protein as well as micro- and macronutrients. Initiation of sapropterin treatment in the newborn period can make exclusive breastfeeding possible. Reports on the efficacy and safety of sapropterin in phenylketonuria (PKU) children under age four are limited in the literature. The purpose of this study is to evaluate the efficacy and safety of sapropterin treatment in infants and children with hyperphenylalaninemia (HPA) and to assess whether genotype analyses are of help in the prediction of responsiveness in these children. Clinical features as well as dietary characteristics were examined in 44 patients undergoing sapropterin treatment. Molecular genetic analysis was performed in 28 of these patients. Phe tolerance increased a median of 2.26-fold (0.88-4.23), from a median of 47.5 mg/kg/day to a median of 114 mg/kg/day (p<0.001). Phe levels could not be kept within normal limits in 5 patients, and thus treatment was stopped due to unsatisfactory metabolic control. In 9 patients, sapropterin treatment was started prior to the initiation of a Phe-restricted diet. Sapropterin treatment was found to be safe and efficacious in patients under age four. Although the BH4 loading test and molecular genetic analysis proved to be useful in detecting responsive patients, these analyses did not enable us to make predictions as to long-term responsiveness.

Two Turkish siblings with MEGDEL syndrome due to novel SERAC1 gene mutation.

Association of 3-methylglutaconic aciduria with impaired oxidative phosphorylation, deafness, encephalopathy, leigh-like lesions on brain imaging, progressive spasticity and dystonia defined as a distinct entity under the name of MEGDEL syndrome. It is an autosomal recessive disorder due to mutation in the serine active site-containing protein 1 (SERAC1). SERAC1 is localized at the interface between the mitochondria and the endoplasmic reticulum in the mitochondria-associated membrane fraction that is essential for phospholipid exchange. It was identified as a key player in the phosphatidylglycerol remodeling that is essential for both mitochondrial function and intracellular cholesterol trafficking. Here we report two new Turkish sibling patients affected with MEGDEL syndrome due to SERAC1 gene mutation. The patients were presented with 3-methylglutaconic acid and 3-methylglutaric aciduria, microcephaly, growth retardation, dysmorphic features, severe sensorineural deafness, progressive spasticity, dystonia, seizures, basal ganglia involvement. Metabolic acidosis, mild hyperammonemia and lactic acidemia were accompanied with clinical findings in newborn period.

Retinitis pigmentosa caused by mutations in the ciliary MAK gene is relatively mild and is not associated with apparent extra-ocular features.

PURPOSE: Defects in MAK, encoding a protein localized to the photoreceptor connecting cilium, have recently been associated with autosomal recessive retinitis pigmentosa (RP). The aim of this study is to describe our detailed clinical observations in patients with MAK-associated RP, including an assessment of syndromic symptoms frequently observed in ciliopathies. METHODS: In this international collaborative study, 11 patients carrying nonsense or missense mutations in MAK were clinically evaluated, including extensive assessment of the medical history, slit-lamp biomicroscopy, ophthalmoscopy, kinetic perimetry, electroretinography (ERG), spectral-domain optical coherence tomography (SD-OCT), autofluorescence imaging and fundus photography. Additionally, we used a questionnaire to evaluate the presence of syndromic features and tested the olfactory function. RESULTS: MAK-associated RP is not associated with syndromic features, not even with subclinical dysfunction of the olfactory apparatus. All patients experienced typical RP symptoms of night blindness followed by visual field constriction. Symptoms initiated between childhood and the age of 43 (mean: 23 years). Although some patients experienced vision loss, the visual acuity remained normal in most patients. ERG and ophthalmoscopy revealed classic RP characteristics, and SD-OCT demonstrated thinning of the overall retina, outer nuclear layer and photoreceptor-pigment epithelium complex. CONCLUSION: Nonsense and missense mutations in MAK give rise to a non-syndromic recessive RP phenotype without apparent extra-ocular features. When compared to other retinal ciliopathies, MAK-associated RP appears to be relatively mild and shows remarkable resemblance to RP1-associated RP, which could be explained by the close functional relation of these proteins.

Association of CFH Y402H polymorphism with both forms of advanced age-related macular degeneration in Turkish patients.

PURPOSE: The purpose of this study was to investigate the association between complement factor H Y402H polymorphism and age-related macular degeneration (AMD) development in a cohort of Turkish patients. METHODS: A total of 182 individuals, including 95 individuals with unrelated late age-related macular degeneration and 87 age-matched healthy individuals as a control group were genotyped with polymerase chain reaction followed by restriction enzyme digestion and direct sequence analysis. The statistical analysis was performed with statistical software R 2.9.2 and epicalc package. RESULTS: The Y402H variant in the CFH gene was found to be associated with late AMD in our study population. Genotypic frequencies were highly different between all patients and control individuals compared for the heterozygotes carrying the risk allele C (AMD patients (CT) 70.5%, control individuals (CT) 54.02%; χ(2)= 5.285, d.f. = 1, p = 0.02). When all AMD patients were compared with the healthy control group, TC heterozygotes showed a significantly increased risk of AMD (O.R = 2.32, CI% 1.23-4.35). CONCLUSION: This study suggests that the CFH Y402H polymorphism is associated with increased risk for both types of end-stage AMD in Turkish patients.