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Meckel-Gruber syndrome is a severe autosomal, recessively inherited disorder characterized by bilateral renal cystic dysplasia, developmental defects of the central nervous system (most commonly occipital encephalocele), hepatic ductal dysplasia and cysts and polydactyly1,2,3. MKS is genetically heterogeneous, with three loci mapped: MKS1, 17q21-24 (ref. 4); MKS2, 11q13 (ref. 5) and MKS3 (ref. 6). We have refined MKS3 mapping to a 12.67-Mb interval (8q21.13-q22.1) that is syntenic to the Wpk locus in rat, which is a model with polycystic kidney disease, agenesis of the corpus callosum and hydrocephalus7,8. Positional cloning of the Wpk gene suggested a MKS3 candidate gene, TMEM67, for which we identified pathogenic mutations for five MKS3-linked consanguineous families. MKS3 is a previously uncharacterized, evolutionarily conserved gene that is expressed at moderate levels in fetal brain, liver and kidney but has widespread, low levels of expression. It encodes a 995–amino acid seven-transmembrane receptor protein of unknown function that we have called meckelin.

Fanconi anemia (FA) is an autosomal recessive chromosomal instability disorder caused by mutations in one of seven known genes (FANCA,C,D2,E,F,G and BRCA2). Mutations in the FANCA gene are the most prevalent, accounting for two-thirds of FA cases. Affected individuals have greatly increased risks of acute myeloid leukemia (AML). This raises the question as to whether inherited or acquired mutations in FA genes might be involved in the development of sporadic AML. Quantitative fluorescent PCR was used to screen archival DNA from sporadic AML cases for FANCA deletions, which account for 40% of FANCA mutations in FA homozygotes. Four heterozygous deletions were found in 101 samples screened, which is 35-fold higher than the expected population frequency for germline FANCA deletions (P

Somatic mosaicism due to reversion of a pathogenic allele to wild type has been described in several autosomal recessive disorders. The best known mechanism involves intragenic mitotic recombination or gene conversion in compound heterozygous patients, whereby one allele serves to restore the wild-type sequence in the other. Here we document for the first time functional correction of a pathogenic microdeletion, microinsertion and missense mutation in homozygous Fanconi anaemia (FA) patients resulting from compensatory secondary sequence alterations in cis. The frameshift mutation 1615delG in FANCA was compensated by two additional single base-pair deletions (1637delA and 1641deIT); another FANCA frameshift mutation, 3559insG, was compensated by 3580insCGCTG; and a missense mutation in FANCC (1749T→G, Leu496Arg) was altered by 1748C→T, creating a cysteine codon. Although in all three cases the predicted proteins were different from wild type, their cDNAs complemented the characteristic hypersensitivity of FA cells to crosslinking agents, thus establishing a functional correction to wild type.

Neurodegenerative disorders with high brain iron include Parkinson disease, Alzheimer disease and several childhood genetic disorders categorized as neuroaxonal dystrophies. We mapped a locus for infantile neuroaxonal dystrophy ( INAD) and neurodegeneration with brain iron accumulation (NBIA) to chromosome 22q12-q13 and identified mutations in PLA2G6, encoding a calcium-independent group VI phospholipase A(2), in NBIA, INAD and the related Karak syndrome. This discovery implicates phospholipases in the pathogenesis of neurodegenerative disorders with iron dyshomeostasis. United States Department of Health & Human Services National Institutes of Health (NIH) - USA NIH Eunice Kennedy Shriver National Institute of Child Health & Human Development (NICHD)-R01HD050832 United States Department of Health & Human Services National Institutes of Health (NIH) - USA NIH National Center for Research Resources (NCRR)-M01RR000334 United States Department of Health & Human Services National Institutes of Health (NIH) - USA NIH National Eye Institute (NEI)-R01EY012353 United States Department of Health & Human Services National Institutes of Health (NIH) - USA NIH National Human Genome Research Institute (NHGRI)-N01HG065403 United States Department of Health & Human Services National Institutes of Health (NIH) - USA NIH National Institute on Aging (NIA)-P30AG008017 United States Department of Health & Human Services National Institutes of Health (NIH) - USA NIH National Center for Research Resources (NCRR)-M01 RR000334 United States Department of Health & Human Services National Institutes of Health (NIH) - USA NIH National Eye Institute (NEI)-R01 EY012353-07, R01 EY012353 United States Department of Health & Human Services National Institutes of Health (NIH) - USA NIH National Human Genome Research Institute (NHGRI)-N01HG65403 United States Department of Health & Human Services National Institutes of Health (NIH) - USA NIH National Institute on Aging (NIA)-P30 AG008017 United States Department of Health & Human Services National Institutes of Health (NIH) - USA NIH Eunice Kennedy Shriver National Institute of Child Health & Human Development (NICHD)-R01 HD050832-01A1, R01 HD050832 Fondazione Telethon-GTF04002

Fanconi anaemia (FA) is an autosomal recessive disorder associated with diverse developmental abnormalities, bone-marrow failure and predisposition to cancer. FA cells show increased chromosome breakage and hypersensitivity to DNA cross-linking agents such as diepoxybutane and mitomycin C. Somatic-cell hybridisation analysis of FA cell lines has demonstrated the existence of at least five complementation groups (FA-A to FA-E), the most common of which is FA-A. This genetic heterogeneity has been a major obstacle to the positional cloning of FA genes by classical linkage analysis. The FAC gene was cloned by functional complementation, and localised to chromosome 9q22.3 (ref. 2), but this approach has thus far failed to yield the genes for the other complementation groups. We have established a panel of families classified as FA-A by complementation analysis, and used them to search for the FAA gene by linkage analysis. We excluded the previous assignment by linkage of an FA gene to chromosome 20q, and obtained conclusive evidence for linkage of FAA to microsatellite markers on chromosome 16q24.3. Strong evidence of allelic association with the disease was detected with the marker D16S303 in the Afrikaner population of South Africa, indicating the presence of a founder effect.

Infantile cholestatic diseases can be caused by mutations in a number of genes involved in different hepatocyte molecular pathways. Whilst some of the essential pathways have a well understood function, such as bile biosynthesis and transport, the role of the others is not known. Here we report the findings of a clinical, biochemical and molecular study of a family with three patients affected with a severe infantile cholestatic disease. A novel homozygous frameshift germline mutation (c.587delG) in the AKR1D1 gene; which encodes the enzyme Δ 4-3-oxosteroid 5β–reductase that is required for synthesis of primary bile acids and is crucial for establishment of normal bile flow, was found in all 3 patients. Although the initial bile acid analysis was inconclusive, subsequent testing confirmed the diagnosis of a bile acid biogenesis disorder. An additional novel homozygous frameshift mutation (c.3391delC) was detected in SKIV2L in one of the patients. SKIV2L encodes a homologue of a yeast ski2 protein proposed to be involved in RNA processing and mutations in SKIV2L were recently described in patients with Tricohepatoenteric syndrome (THES). A combination of autozygosity mapping and whole-exome-sequencing allowed the identification of causal mutations in this family with a complex liver phenotype. Although the initial 2 affected cousins died in the first year of life, accurate diagnosis and management of the youngest patient led to successful treatment of the liver disease and disease-free survival.

Nat. Genet. 38, 752–754 (2006); published online 18 June 2006; corrected after print 17 July 2006 In the version of this article initially published, the authors neglected to acknowledge sample contributions. Samples were obtained from the “Cell line and DNA bank from patients affected by genetic diseases” collection at the Giannina Gaslini Institute (http://www.gaslini.org/labdppm.htm) supported by Italian Telethon grants (project #GTF04002).