Clinical features of Bardet-Biedl syndrome

Phenotypic expression of Bardet-Biedl syndrome in patients homozygous for the common M390R mutation in the BBS1 gene

PURPOSE

To characterize the phenotype of Bardet-Biedl syndrome (BBS) patients homozygous for the BBS1 M390R mutation.

METHODS

Three patients [PT1, F, 27 years old (yo) at last examination, 14-year follow-up (F/U) PT2, F, 15-yo PT3, M, 15-yo, both 1-year F/U] underwent eye exams, Goldmann visual fields (GVFs), dark- (DA) and light-adapted (LA) electroretinograms (ERGs), spectral domain optical coherence tomography (SD-OCT) and fundus autofluorescence (FAF). Vision and systemic history were also collected.

RESULTS

All patients had night blindness, hyperopic astigmatism, ptosis or mild blepharospasm, foot polydactyly, 5th finger clinodactyly, history of headaches, and variable, diet-responsive obesity. Two had asthma, PT1 was developmentally delayed, PT2 had Asperger-like symptoms, and PT3 had normal cognition. At age 14, acuity was 20/100 in PT1, who had nystagmus since age 2, 20/40 in PT2 and 20/30 in PT3. By 27yo PT1 progressed to 20/320, by 15 yo PT2 was 20/60 and PT3 remained stable. PT1 had well preserved peripheral GVFs, with minimal progression over 10 years of F/U. PT2 and PT3 presented with ring scotomas and I4e<5°. All patients had severe generalized visual sensitivity depression. ERGs were consistently recordable (also rod ERG in PT3 after 60 min DA), but progressed to non-recordable in PT1. Mixed DA ERGs exhibited electronegativity. In PT3, this was partly due to a bleaching effect during bright-flash DA averaging, partly to ON≫OFF LA response compromise. PT2 and 3 had, on SD-OCTs, generalized macular thinning, normal retinal lamination, and widespread photoreceptor outer/inner segment attenuation except foveally, and multiple rings of abnormal FAF configuring a complex bull's eye-pattern. PT1 had macular atrophy. All patients also had peripapillary nerve fiber layer thickening.

CONCLUSIONS

The observed phenotype matches very closely that reported in patients by Azari et al. (IOVS 2006) and in the Bbs1-M390R knock-in mouse model, and expands it to the characterization of important ERG response characteristics that provide insight in the pathogenesis of retinopathy in these patients. Our findings confirm the consistent pathogenicity of the BBS1 M390R mutation.

A review of the literature of Bardet-Biedl disease and report of three cases associated with metabolic syndrome and diagnosed after the age of fifty

Bardet-Biedl syndrome (BBS) is a genetic autosomal-recessive disease (formerly grouped with Laurence-Moon-Biedl syndrome but considered today as a separate entity) characterized by abdominal obesity, mental retardation, dysphormic extremities (syndactyly, brachydactyly or polydactyly), retinal dystrophy or pigmentary retinopathy, hypogonadism or hypogenitalism (limited to male patients) and kidney structural abnormalities or functional impairment. The expression and severity of the various clinical BBS features show inter- and intrafamilial variability. This study focuses on three cases of familial BBS--two sisters and one brother (66, 64 and 51 years of age, respectively)--with the main cardinal findings of the disease plus a classic 'metabolic syndrome' (characterized by abdominal obesity, atherogenic dyslipidaemia, raised blood pressure, insulin resistance with or without glucose intolerance, and prothrombotic risk and proinflammatory states). One female patient (not affected by reproductive dysfunction) had three healthy offspring, while the other two patients were unmarried. Another severely affected brother died at 70 years of age; two other brothers are lean but affected by nephropathy, retinopathy, slight mental retardation, polydactyly, hypertension and thrombotic diseases, and had healthy offspring. BBS is a rather rare but severe syndrome that is often mis- or undiagnosed. Ophthalmologists, endocrinologists and nephrologists should be aware of BBS because of its adverse prognosis--early onset of blindness, associated findings of metabolic syndrome and increased vascular risk, and severe renal impairment (the most frequent cause of reduced survival and death early in life).

Three children with a syndrome of obesity and overgrowth, atypical psychosis, and seizures: a problem in neuropsychopharmacology

Three children presented with a complex syndrome of atypical psychotic and extremely immature behavior, obesity and overgrowth, borderline retardation, and seizures (prominent in two). Weight overgrowth exceeded height overgrowth and was stratospheric (up to 8 SD above mean). Obesity seemed related to lack of satiety. The cases fit no known condition: hypothalamic damage, Sotos' syndrome, and Prader-Willi syndrome were excluded. Empirical treatment with anticonvulsants (carbamazepine and acetazolamide) together with psychotropic agents (selective serotonin reuptake inhibitors and risperidone) controlled seizures, improved behavior, and stopped weight gain in each patient. We have not found this syndrome previously described. The etiology is unknown: perinatal encephalopathy could be a factor in the two patients with prominent seizures; in the third, familial major affective disorder is implicated. Medication responses suggest a low-serotonin state underlying the lack of satiety, an imbalance of serotonin and noradrenergic modulation in the hypothalamus, and epileptogenic disorders (or affective disorder responsive to anticonvulsants in one case) involving these same systems.

Bardet-Biedl syndrome

This case report describes the presentation of a patient with Bardet-Biedl syndrome. Bardet-Biedl Syndrome is an autosomal recessive condition that includes retinal dystrophy, dystrophic extremities (commonly polydactyly), obesity, hypogenitalism, and renal disease. Cognitive deficit has also been considered part of the syndrome. The historically associated Laurence-Moon syndrome includes spastic paraparesis but not the obesity and polydactyly. They are now considered separate conditions. The most common feature of Bardet-Biedl syndrome is retinal dystrophy. The appearance of the retina in the condition is quite variable with typical retinitis pigmentosa being present in only a minority of cases. The associated optic atrophy can be primary in nature and might play a role in the decreased central vision. Diagnosis of the condition is important for visual prognosis and low vision management. The renal disease often goes undetected until specific radiological testing is done after diagnosis of Bardet-Biedl syndrome. This is significant in that early death often occurs in this condition because of the renal disease.

Evaluation and molecular characterization of EHD1, a candidate gene for Bardet-Biedl syndrome 1 (BBS1)

Bardet-Biedl Syndrome (BBS) is an autosomal recessive disorder characterized by developmental abnormalities including mental retardation, obesity, retinitis pigmentosa, polydactyly, short stature, and hypogenitalism. To date, five BBS loci have been identified. BBS1, located on 11q13, is reported to be the most prevalent form of BBS in the Caucasian population. A positional cloning approach is being used to identify the gene responsible for BBS1. EHD1, a new member of the EH-domain containing proteins, was identified in this study as lying within the BBS1 disease interval. RNA analysis of many tissues revealed that expression of EHD1 is ubiquitous, with elevated levels in the testis. The genomic structure of EHD1 was elucidated by direct BAC sequencing. Following identification of the intron/exon boundaries, mutational analysis was performed by single strand conformation polymorphism and direct sequencing of affected individuals from several large kindreds linked to the BBS1 locus, as well as a cohort of unrelated probands. No disease-causing mutations were identified in this analysis, but several polymorphisms were found.

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.

Alström syndrome. Report of 22 cases and literature review

OBJECTIVE

The authors report 22 cases of Alström syndrome (AS), which is the largest series to date. Only 37 cases have been reported in the world literature since 1959. The authors review the clinical features and compare these with the overlapping condition of Bardet-Biedl syndrome. Their aim is to clarify the AS phenotype and to increase awareness of the early features.

DESIGN

A retrospective case series.

PARTICIPANTS

All patients (22) with a diagnosis of AS admitted to the authors' hospital in the past 10 years were included in this review.

INTERVENTION

This is principally a review of ocular features, but other features are recorded and discussed.

MAIN OUTCOME MEASURES

Features noted included age at onset of visual symptoms, presence of photophobia, visual acuity, and electroretinogram findings. Nonocular features recorded included cardiac status, weight and height, hearing, and presence of diabetes mellitus.

RESULTS

Cardiomyopathy presenting in infancy has only been recognized recently to be a feature of AS. Of the authors' cases, 18 of 22 had infantile cardiomyopathy. In the authors' tertiary referral institution, there is an ascertainment bias toward younger patients and especially those with pathology that is other than ocular pathology. In addition, AS is difficult to recognize in childhood without the development of infantile cardiomyopathy. Alström syndrome often is not recognized until diabetes mellitus develops in the second or third decade. Initially, a diagnosis of cone-rod dystrophy, achromatopsia, Leber's congenital amaurosis, or Bardet-Biedl syndrome may be made. In AS, there is a severe infantile retinal dystrophy. The electroretinogram is absent or attenuated with better preserved rod than cone function. The retinal dystrophy is progressive with the patient's visual acuity of 6/60 or less by 10 years of age and no light perception by 20 years of age.

CONCLUSIONS

A diagnosis of AS should be considered in infantile cone and rod retinal dystrophy, particularly if the weight is above the 90th percentile (16 of 18 cases) or if there is an infantile cardiomyopathy (18 of 22 cases).