Neuropathy target esterase impairments cause Oliver-McFarlane and Laurence-Moon syndromes.

BACKGROUND: Oliver-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. METHODS: Whole-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. RESULTS: Eight 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. CONCLUSIONS: Previously, 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.

Laurence-Moon-Biedl syndrome with vaginal atresia.

A 15-year-old girl presented with the rare Laurence-Moon-Biedl syndrome, accompanied by vaginal atresia, and cervical dysgenesis. She was treated by hysterectomy and construction of a neovagina with bilateral pudendal thigh flaps. Two brothers and a sister (one of twins) were unaffected but the remaining brother also had the disease.

Hydrometrocolpos and polydactyly: a common neonatal presentation of Bardet-Biedl and McKusick-Kaufman syndromes.

McKusick-Kaufman syndrome (MKKS) is a rare, recessively inherited syndrome reported mainly in young children and is characterised by vaginal atresia with hydrometrocolpos, postaxial polydactyly, and congenital heart defect. Bardet-Biedl syndrome (BBS) is the generic name for a genetically heterogeneous group of autosomal recessive disorders characterised by retinal dystrophy or retinitis pigmentosa (appearing usually between 10 and 20 years of age), postaxial polydactyly, obesity, nephropathy, and mental disturbances, or, occasionally, mental retardation. Typically, MKKS is diagnosed (and reported) in very young children, whereas the diagnosis of BBS often is delayed to the teenage years. We report here a series of nine patients diagnosed in infancy with MKKS because of the presence of vaginal atresia and postaxial polydactyly, who later developed obesity and retinal dystrophy, thus turning out to be instances of BBS. The overlap of BBS and MKKS is a real diagnostic pitfall and its importance has to be stressed, for genetic counselling, for clinical management and follow up, and for molecular approaches. The diagnosis of MKKS should be considered with caution in all published cases described exclusively in the neonatal period and in those with mental retardation. We strongly recommend all children seen in infancy with a diagnosis of MKKS to be re-evaluated for RP and other signs of BBS.

The cloning and developmental expression of unconventional myosin IXA (MYO9A) a gene in the Bardet-Biedl syndrome (BBS4) region at chromosome 15q22-q23.

Bardet-Biedl Syndrome (BBS) is a heterogeneous, autosomal recessive disorder characterized by mental retardation, obesity, retinitis pigmentosa, syndactyly and/or polydactyly, short stature, and hypogenitalism and is caused by mutations at a number of distinct loci. Using a positional cloning approach for identifying the BBS4 (chromosome 15) gene, we identified and cloned an unconventional myosin gene, myosin IXA (HGMW-approved symbol MYO9A). Since mutations in unconventional myosins are known to cause several human diseases, and since mutations of unconventional myosin VIIa cause retinal degeneration, we evaluated myosin IXA as a candidate for BBS. We exploited PCR-based techniques to clone a 8473-nt cDNA for myosin IXA. A 7644-bp open reading frame predicts a protein with all the hallmarks of class IX unconventional myosins. Human Northern blot analysis and in situ hybridization of mouse embryos reveal that myosin IXA is expressed in many tissues consistent with BBS. Intron/exon boundaries were identified, and myosin IXA DNA and RNA from BBS4 patients were evaluated for mutation.

Selection for carriers of recessive diseases: a common phenomenon?

Several autosomal recessive disorders are present in high frequency in isolated populations because of either multiple allelic mutations or mutations in different genes. These observations are best explained by selection, which may be an important mechanism in the determination of the distribution of genetic disorders.

The ovo gene required for cuticle formation and oogenesis in flies is involved in hair formation and spermatogenesis in mice.

The Drosophila svb/ovo gene gives rise to differentially expressed transcripts encoding a zinc finger protein. svb/ovo has two distinct genetic functions: shavenbaby (svb) is required for proper formation of extracellular projections that are produced by certain epidermal cells in late-stage differentiation; ovo is required for survival and differentiation of female germ cells. We cloned a mouse gene, movo1 encoding a nuclear transcription factor that is highly similar to its fly counterpart in its zinc-finger sequences. In mice, the gene is expressed in skin, where it localizes to the differentiating cells of epidermis and hair follicles, and in testes, where it is present in spermatocytes and spermatids. Using gene targeting, we show that movo1 is required for proper development of both hair and sperm. movo1(-/-) mice are small, produce aberrant hairs, and display hypogenitalism, with a reduced ability to reproduce. These mice also develop abnormalities in kidney, where movo1 is also expressed. Our findings reveal remarkable parallels between mice and flies in epidermal appendage formation and in germ-cell maturation. Furthermore, they uncover a phenotype similar to that of Bardet-Biedl syndrome, a human disorder that maps to the same locus as human ovo1.

Cloning of a novel C-terminal kinesin (KIFC3) that maps to human chromosome 16q13-q21 and thus is a candidate gene for Bardet-Biedl syndrome.

Kinesins are a large superfamily of microtubule motors that mediate specific motile processes. In a previous study, we identified 11 kinesin family members in the retina and retinal pigment epithelium (RPE) of the striped bass, Morone saxatilus. We have now identified, cloned, and sequenced the human homologue (KIFC3) of the most abundantly expressed retinal kinesin from that study, the C-terminal kinesin FKIF2. An antibody raised against an FKIF2 peptide cross-reacted with an approximately 80-kDa protein in human retina, RPE, kidney, and lung. Since microtubule-dependent processes are critical to the function and morphogenesis of the photoreceptors and RPE, the abundantly expressed KIFC3 was considered to be a potential candidate gene for causing human retinal degeneration. Chromosomal localization of the KIFC3 gene revealed that it maps to chromosome 16q13-q21, within the critical region for a Bardet-Biedl syndrome locus (BBS2). Bardet-Biedl syndrome is a genetically heterogeneous, autosomal recessive disorder characterized by retinal dystrophy, polydactyly, obesity, hypogonadism, renal abnormalities, and mental retardation. The chromosomal localization and expression pattern of KIFC3 suggest that it may be an excellent candidate for families linked to BBS2.

A transcript map of an 800-kb region on human chromosome 11q13, part of the candidate region for SCA5 and BBS1.

The exon-amplification method was used to identify putative transcribed sequences from an 800-kb region that includes the genes for phospholipase Cbeta3 and PYGM on human chromosome 11q13. The clone contig consisted of ten cosmids, three bacterial artificial chromosomes, and one P1 artificial chromosome. A total of 83 exons were generated of which 23 were derived from known genes and expressed sequence tags (ESTs). Five different EST cDNA clones were identified and mapped on the contig. One is a homolog of the human p70S6 kinase (p70s6 k) gene whose function involves the translational regulation of ribosomal protein synthesis and thereby impacts on ribosomal biogenesis. The gene for p70s6 k is expressed universally, including within adipose cells and retina, and it could play a role in Bardet-Biedl syndrome type 1, which has been mapped to 11q13.

Intrafamilial variation of the phenotype in Bardet-Biedl syndrome.

AIMS: To describe the variation of the phenotype within families with several individuals with Bardet-Biedl syndrome. METHODS: The phenotypes of affected siblings in 11 Scandinavian families with two or more members who had at least three of the features: retinal dystrophy, polydactyly, obesity, hypogenitalism, and mental retardation, were compared [corrected]. Individuals without retinal dystrophy were excluded. RESULTS: Intrafamilial variation of expressivity of the features obesity, polydactyly, abnormal radiograms of the extremities, hypogenitalism, short stature, paraplegia, and dental abnormalities was found. The retinal dystrophy varied with respect to both the onset of symptoms and the course of the disease. The morphology of the fundus, however, was consistent within the families. The disorder showed statistically significant genetic linkage to the BBS4 locus on chromosome 15 in the affected siblings in two of the families, but the clinical features in these patients did not differ from the other cases of Bardet-Biedl syndrome. CONCLUSION: Comparison of siblings with the Bardet-Biedl syndrome showed variation of the typical features. In addition, the course of retinal dystrophy varied. No distinctive clinical features were found to separate the BBS4 phenotype from the remaining patients.

Evaluation of the human gene encoding recoverin in patients with retinitis pigmentosa or an allied disease.

PURPOSE: To determine whether defects in the human recoverin gene cause retinitis pigmentosa (RP) or an allied disease such as Usher syndrome, Leber congenital amaurosis, or the Bardet-Biedl syndrome. METHODS: Single-strand conformation polymorphism analysis and direct genomic sequencing techniques were used to screen 596 unrelated patients, comprising 167 patients with dominant RP, 168 with recessive RP, and 261 with an allied disease. RESULTS: Four sequence variants were discovered. The first was a missense change (Ala200Thr) found in one family with autosomal dominant RP and in one family with autosomal recessive RP; it did not segregate with disease. The second was a silent, single-base variation affecting codon Ser24 with a minor allele frequency of approximately 0.5%. The third was a silent, single-base variation affecting codon Va1122. The fourth was a single-nucleotide substitution in intron 2, 11 bp upstream of exon 3. CONCLUSIONS: The authors found no evidence that mutations in the recoverin gene are a cause of RP or another of the hereditary retinal diseases studied. The human phenotype associated with mutations of the recoverin gene remains unknown.

Bardet-Biedl syndrome: a molecular and phenotypic study of 18 families.

The autosomal recessive disorder Bardet-Biedl syndrome is characterised by retinal degeneration, polydactyly, obesity, mental retardation, hypogenitalism, renal dysplasia, and short stature. It is heterogeneous with at least four gene loci (BBS1-4) having been mapped to date. We have studied 18 multiply affected families noting the presence of both major and minor manifestations. Using a fluorescently based PCR technique, we genotyped each family member and assigned linkage to one of the four loci. Given this degree of heterogeneity we hoped to find phenotypic differences between linkage categories. We found 44% of families linked to 11q13 (BBS1) and 17% linked to 16q21 (BBS2). Only one family was linked to 15q22 (BBS4) and none to 3p12. We conclude that BBS1 is the major locus among white Bardet-Biedl patients and that BBS3 is extremely rare. Only subtle phenotypic differences were observed, the most striking of which was a finding of taller affected offspring compared with their parents in the BBS1 category. Affected subjects in the BBS2 and 4 groups were significantly shorter than their parents. Twenty eight percent of pedigrees did not show linkage to any known locus, evidence for at least a fifth gene. We conclude that the different genes responsible for Bardet-Biedl syndrome may influence growth characteristics such as height.

Full-field electroretinograms in individuals with the Laurence-Mood-Bardet-Biedl syndrome.

PURPOSE: To evaluate rod and cone function in individuals with the Laurence-Moon-Bardet-Biedl syndrome. METHODS: We obtained a full-field electroretinograms in 36 patients. If responses less than 10 microV were recorded with single white flashes a special techniques with narrow band filter and computer averaging was used. RESULTS: No rod responses to dim blue light could be obtained in any of the patients. Residual cone flicker responses were measurable in 28 of the individuals. Those with amplitudes < 0.05 microV were significantly older than those with amplitudes > 1.00 microV. The ERG pattern was consistent within affected pairs of siblings in 8 families. CONCLUSION: The retinal dystrophy in Laurence-Moon-Bardet-Biedl syndrome is primarily a rod-cone dystrophy, but even cone flicker amplitudes are severely reduced with further progression with age. There is no intrafamilial variability of the electroretinograms in affected siblings.

Electroretinographic alterations in the Laurence-Moon-Bardet-Biedl phenotype.

Maximal 0.5-Hz and cone 30-Hz ERG responses were recorded from 19 patients showing a Laurence-Moon-Bardet-Biedl (LMDD) phenotype. Off-line averaging of 80 to 100 iterations was routinely performed. When needed, our previously described low-noise techniques and off-line fast Fourier transform procedures were used. The maximal ERG response was non-detectable in 52.6% of cases. About half of the recordable signals were below 5% of the lower normal amplitudes. Cone 30-Hz ERGs were measurable in 64.7% of cases. Of these, 63% of tracings were below 5% of the lower normal range. In most cases no dystrophic pattern was definable, due to severe reduction of both signals. Statistical analyses showed no correlation between ERG amplitudes and residual visual field areas. Clinical and electroretinographic observations suggest that retinopathy in most LMBB patients is a widespread form of degeneration, initially affecting rods but rapidly involving cones as well. However, there are also cases with a clear-cut cone-rod pattern, with fairly well preserved maximal ERG responses. The lack of correlation between maximal ERG responses and visual field residual areas, different from non-syndromic retinitis pigmentosa (RP) patients, could be related either to a low reliability of visual field testing in LMBB patients or to mechanisms accounting for the ongoing retinal degeneration in LMBB syndrome that are different from those of pure RP. Variable findings are in line with the documented genetic heterogeneity of the syndrome.