Novel biallelic splice-site BBS1 variants in Bardet-Biedle syndrome: a case report of the first Japanese patient

Bardet–Biedl syndrome associated with novel compound heterozygous variants in BBS12 gene

BACKGROUND

Bardet-Biedl syndrome (BBS) is a rare autosomal recessive ciliopathy characterized by 6 primary features of rod-cone dystrophy, central obesity, polydactyly, cognitive impairment, hypogonadism and/or genitourinary malformations, and kidney abnormalities. At least 21 genes associated with BBS have been reported. To date, BBS associated with BBS12 variants has never been described in the Japanese population. We report a Japanese infant female with BBS with compound heterozygous BBS12 variants.

METHODS

In addition to the pediatric examination, fundus photography, full-field electroretinogram(ffERG) and whole exome sequencing (WES) were underwent.

RESULTS

The infant exhibited obesity, polydactyly, cognitive impairment, genitourinary malformations, and kidney dysfunction. At the age of 2 years, ffERG revealed severe reduction in both rod- and cone-mediated electroretinographic responses consistent with a severe form of rod-cone dystrophy, with minimal retinal abnormalities. WES revealed novel compound heterozygous BBS12 variants (c.591T > A, p.Tyr197* and c.1372dupA, p.Thr458Asnfs*5) in the infant. Her parents carried each of the variants, as confirmed by Sanger sequencing.

CONCLUSIONS

The current observations will contribute to an expanded understanding of genotype-phenotype associations in BBS12-associated BBS.

Identification of a Novel Homozygous Missense (c.443A>T:p.N148I) Mutation in BBS2 in a Kashmiri Family with Bardet-Biedl Syndrome

Background

Bardet-Biedl syndrome (BBS) is a rare autosomal recessive inherited disorder with distinctive clinical feature such as obesity, degeneration of retina, polydactyly, and renal abnormalities. The study was aimed at finding out the disease-causing variant/s in patients exhibiting clinical features of BBS.

Methods

The identification of disease-causing variant was done by using whole exome sequencing on Illumina HiSeq 4000 platform involving the SeqCap EZ Exome v3 kit (Roche NimbleGen). The identified variant was further validated by Sanger sequencing.

Results

WES revealed a novel homozygous missense mutation (NM_031885: c.443A>T:p.N148I) in exon 3 of the BBS2 gene. Sanger sequencing confirmed this variant as homozygous in both affected subjects and heterozygous in obligate parents, demonstrating autosomal recessive inheritance pattern. To the best of our knowledge, this variant was not present in literature and all publically available databases. The candidate variant is predicted to be pathogenic by a set of in-silico softwares.

Conclusion

Clinical and genetic spectrum of BBS and BBS-like disorders is not completely defined in the Pakistani as well as in Kashmiri population. Therefore, more comprehensive genetic studies are required to gain insights into genotype-phenotype associations to facilitate carrier screening and genetic counseling of families with such disorders.

Vitamin A deficiency after prolonged intake of an unbalanced diet in a Japanese hemodialysis patient

BACKGROUND

In industrialized countries, vitamin A deficiency (VAD) is extremely rare, except association with bariatric surgeries and hepatobiliary disorders. It is unusual that VAD develops during hemodialysis due to reduced glomerular filtration of vitamin A-binding protein. We reported the case of a 58-year-old Japanese male hemodialysis patient diagnosed with VAD.

CASE PRESENTATION

The patient undergoing hemodialysis for more than 15 years presented with progressive photophobia and night blindness and was ophthalmologically examined. He denied a history of cancer or hepatobiliary disease and reported that he loved eating prepackaged noodle bowls and foods, with prolonged low intake of fruits/vegetables. He had good visual acuity. Fundus images showed numerous white dots in the midperipheral retinae, but no degenerative changes. In baseline full-field electroretinography (ERG), b-wave responses were extremely reduced in rod ERG, a-wave amplitudes in standard-flash/strong-flash ERG were reduced to 20-25% of our controls, a- and b-wave amplitudes in cone ERG were reduced to 40-50% of the controls. Whole-exome sequencing identified no pathogenic variant for any inherited retinal disorder. He was diagnosed with VAD because of reduced serum vitamin A levels and treated with retinol palmitate. Two months after treatment commencement, the serum vitamin A level was within the normal range. Full-field ERG showed that the scotopic ERG responses markedly improved compared with baseline.

CONCLUSIONS

This is the first report of VAD associated with undernutrition in the Japanese hemodialysis population.

Clinical characteristics and ultra-widefield fundus image analysis of two siblings with Bardet-Biedl syndrome type 1 p.Met390Arg variant

Purpose

To present the case of two siblings with a genetic diagnosis of Bardet Biedl syndrome (BBS) type 1, yet different clinical profiles and disease manifestations.

Observations

Sequencing analysis revealed a p.Met390Arg pathogenic variant in the BBS1 gene of both patients, as well as several additional variants of uncertain significance Patient 1 was 41 years old, had three primary (cone-rod dystrophy, hypogonadism, and truncal obesity) and three secondary (arterial hypertension, strabismus, and astigmatism) BBS features. He also had insulin resistance, as well as low levels of total testosterone and cortisol. Patient 2 was 43 years old, had two primary (cone-rod dystrophy and truncal obesity), and four secondary (arterial hypertension, diabetes mellitus, strabismus, and astigmatism) BBS features. Both patients had severe maculopathy; however, patient 1 had bone-spicules that extended up to the mid-periphery, in a perivenular pattern, and significant vascular attenuation with "ghost vessel" appearance towards the temporal periphery, a feature that was absent on patient 2.

Conclusions and Importance

The intrafamilial phenotypic variability among our patients supports the hypothesis that BBS is a disease with genetic, hormonal, and environmental triggers interacting to produce phenotypic variability. Although our report may not establish a definite relationship between environmental and genetic influences, their role should be explored in future studies.