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BackgroundOliver-McFarlane syndrome is characterised by trichomegaly, congenital hypopituitarism and retinal degeneration with choroidal atrophy. Laurence-Moon syndrome presents similarly, though with progressive spinocerebellar ataxia and spastic paraplegia and without trichomegaly. Both recessively inherited disorders have no known genetic cause.MethodsWhole-exome sequencing was performed to identify the genetic causes of these disorders. Mutations were functionally validated in zebrafish pnpla6 morphants. Embryonic expression was evaluated via in situ hybridisation in human embryonic sections. Human neurohistopathology was performed to characterise cerebellar degeneration. Enzymatic activities were measured in patient-derived fibroblast cell lines.ResultsEight mutations in six families with Oliver-McFarlane or Laurence-Moon syndrome were identified in the PNPLA6 gene, which encodes neuropathy target esterase (NTE). PNPLA6 expression was found in the developing human eye, pituitary and brain. In zebrafish, the pnpla6 curly-tailed morphant phenotype was fully rescued by wild-type human PNPLA6 mRNA and not by mutation-harbouring mRNAs. NTE enzymatic activity was significantly reduced in fibroblast cells derived from individuals with Oliver-McFarlane syndrome. Intriguingly, adult brain histology from a patient with highly overlapping features of Oliver-McFarlane and Laurence-Moon syndromes revealed extensive cerebellar degeneration and atrophy.ConclusionsPreviously, PNPLA6 mutations have been associated with spastic paraplegia type 39, Gordon-Holmes syndrome and Boucher-Neuhäuser syndromes. Discovery of these additional PNPLA6-opathies further elucidates a spectrum of neurodevelopmental and neurodegenerative disorders associated with NTE impairment and suggests a unifying mechanism with diagnostic and prognostic importance.

Abstract Background Oculocutaneous 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. Methods We 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. Results Screening 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. Conclusions Our 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.

Alleles associated with lower levels of LDL cholesterol (LDL-C) have recently been associated with an increased risk of type 2 diabetes (T2D), highlighting the complex relationship between LDL-C and diabetes. This observation begs the question of whether LDL-C-raising alleles are associated with a decreased risk of T2D. This issue was recently addressed in a large familial hypercholesterolemia (FH) screening study, which reported a lower prevalence of self-reported diabetes in FH subjects than in age-matched relatives without FH. To extend this observation, we tested the association of FH with diabetes status and glycemia in a large Amish population enriched for the FH-associated APOB R3527Q variant that included 640 APOB R3527Q carriers and 4,683 noncarriers. Each copy of the R3527Q T allele was associated with a 74.9 mg/dL increase in LDL-C. There was little difference in T2D prevalence between subjects with (5.2%) and without (4.5%) the R3527Q allele (P = 0.23), and there was no association between R3527Q variant and impaired fasting glucose, fasting glucose or insulin, or oral glucose tolerance test-derived measures. Our data provide no evidence supporting an association between the APOB R3527Q variant and T2D or glycemia and highlight the asymmetry of the LDL-C-T2D relationship and/or the gene/variant-dependent specificity of the LDL-C-T2D association. [ABSTRACT FROM AUTHOR]