The clinical value of optical genome mapping in the rapid characterization of RB1 duplication and 15q23q24.2 triplication, for more appropriate prenatal genetic counselling.

BACKGROUND: Despite recent advances in prenatal genetic diagnosis, medical geneticists still face considerable difficulty in interpreting the clinical outcome of copy-number-variant duplications and defining the mechanisms underlying the formation of certain chromosomal rearrangements. Optical genome mapping (OGM) is an emerging cytogenomic tool with proved ability to identify the full spectrum of cytogenetic aberrations. METHODS: Here, we report on the use of OGM in a prenatal diagnosis setting. Detailed breakpoint mapping was used to determine the relative orientations of triplicated and duplicated segments in two unrelated foetuses harbouring chromosomal aberrations: a de novo 15q23q24.2 triplication and a paternally inherited 13q14.2 duplication that overlapped partially with the RB1 gene. RESULTS: OGM enabled us to suggest a plausible mechanism for the triplication and confirmed that the RB1 duplication was direct oriented and in tandem. This enabled us to predict the pathogenic consequences, refine the prognosis and adapt the follow-up and familial screening appropriately. CONCLUSION: Along with an increase in diagnostic rates, OGM can rapidly highlight genotype-phenotype correlations, improve genetic counselling and significantly influence prenatal management.

IN VIVO OBSERVATION OF RETINAL VASCULAR DEPOSITS USING ADAPTIVE OPTICS IMAGING IN FABRY DISEASE.

PURPOSE: To report a novel finding in patients with Fabry disease, that is, the observation by adaptive optics ophthalmoscopy of intracellular lipidic deposits in retinal vessels. METHODS: Observational two-center case series. Eighteen patients with genetically proven Fabry disease underwent flood-illumination adaptive optics ophthalmoscopy imaging (rtx1; Imagine Eyes, Orsay, France) of retinal vessels. RESULTS: Fourteen patients (78% of all patients; 7 of the 10 women and 7 of the 8 men) showed paravascular punctuate or linear opacities in both eyes. In the least-affected patients, these were seen only in the wall of precapillary arterioles as discrete spots of 5 µm to 10 µm large, whereas in those more severely affected, capillaries and first-order vessels were also involved with diffuse opacification of the wall. These deposits sometime showed a striated pattern, suggesting colocalization with vascular smooth muscle cells. CONCLUSION: Adaptive optics ophthalmoscopy of retinal vessels may be of interest for patients with Fabry disease, providing noninvasive, gradable evaluation of microvascular involvement.

Strong increase of leukocyte apha-galactosidase A activity in two male patients with Fabry disease following oral chaperone therapy.

BACKGROUND: Fabry disease (OMIM 301500) is an X-linked disorder caused by alpha-galactosidase A (α-Gal A) deficiency. The administration of a pharmacologic chaperone (migalastat) in Fabry patients with amenable mutations has been reported to improve or stabilize organ damages and reduce lyso-Gb3 plasma level. An increase of α-Gal A activity has been observed in vitro in cells expressing amenable GLA mutations when incubated with migalastat. The impact of the drug on α-Gal A in vivo activity has been poorly studied. METHODS: We conducted a retrospective analysis of two unrelated male Fabry patients with p.Asn215Ser (p.N215S) variant. RESULTS: We report the important increase of α-Gal A activity in blood leukocytes reaching normal ranges of activity after about 1 year of treatment with migalastat. Cardiac parameters improved or stabilized with the treatment. CONCLUSION: We confirm in vivo the effects of migalastat that have been observed in N215S carriers in vitro. The increase of α-Gal A activity may be the strongest marker for biochemical efficacy. The normalization of enzyme activity could become the new therapeutic target to achieve.