Screening for RFC-1 pathological expansion in late-onset ataxias: a contribution to the differential diagnosis

We screened 62 late-onset ataxia patients for the AAGGG pathological expansion in the RFC-1 gene that, when biallelic, causes Cerebellar Ataxia, Neuropathy, Vestibular Areflexia Syndrome (CANVAS). Nine patients tested positive. Six had a previous diagnosis of sporadic adult-onset ataxia (SAOA) and three of multisystem atrophy type C (MSA-C). Further six patients were heterozygous for the pathological RFC-1 expansion, four with an initial diagnosis of MSA-C and two of SAOA. In comparison with CANVAS, MSA-C patients had faster progression and shorter disease duration to walking with aids. An abnormal DaTscan does not seem to contribute to differential diagnosis between CANVAS and MSA-C.

Risk of cancer in heterozygous relatives of patients with Fanconi anemia

PURPOSE

Fanconi anemia (FA) is a cancer-prone inherited bone marrow failure syndrome caused by biallelic pathogenic variants in one of >22 genes in the FA/BRCA DNA repair pathway. A major concern is whether the risk of cancer is increased in individuals with a single pathogenic FA gene variant.

METHODS

We evaluated the risk of cancer in the relatives of patients with FA in the National Cancer Institute Inherited Bone Marrow Failure Syndrome cohort. We genotyped all available relatives and determined the rates, types of cancer and the age of patients at cancer diagnosis. We calculated the observed-to-expected (O/E) cancer ratios using data from the Surveillance, Epidemiology, and End Results Program adjusted for age, sex, and birth cohort.

RESULTS

The risk of cancer was not increased among all FA relatives and FA heterozygotes (O/E ratios of 0.78 and 0.79, respectively). In particular, the risk of cancer was not increased among FANCA or FANCC heterozygotes (O/E ratios of 0.92 and 0.71, respectively). Relatives did not have typical FA cancers, and age at cancer diagnosis was not younger than expected.

CONCLUSION

Understanding the risk of cancer in individuals with single pathogenic FA variants is critical for counseling and management. We did not find increased risk of cancer in these individuals. These findings do not extend to the known cancer predisposition autosomal dominant FA genes, namely BRCA1, BRCA2, PALB2, BRIP1, and RAD51C.

Diversity of ATM gene variants: a population-based genome data analysis for precision medicine

BACKGROUND

Ataxia-telangiectasia (AT) is a rare autosomal recessive disorder that causes deficiency or dysfunction of the ataxia-telangiectasia mutated (ATM) protein. Not only AT patients, but also certain ATM heterozygous mutation carriers show a significantly reduced life expectancy due to cancer and ischemic heart disease; in particular, female carriers having particular alleles have an increased risk of breast cancer. The frequency of such risk heterozygotes at a population level remains to be fully determined, and evidence-based preventive medical guidelines have not yet been established.

METHODS

Using the 3.5KJPNv2 allele frequency panel of Japanese Multi Omics Reference Panel v201902, which shows single-nucleotide variant (SNV) and insertion/deletion (INDEL) allele frequencies from 3552 Japanese healthy individuals, we investigated the diversity of ATM gene variants.

RESULTS

We detected 2845 (2370 SNV and 475 INDEL) variants in the ATM gene, including 1338 (1160 SNV and 178 INDEL) novel variants. Also, we found a stop-gained SNV (NC_000008.11:g.108115650G > A (p.Trp266*)) and a disruptive-inframe-deletion (NC_000008.11:g. 108181014AAGAAAAGTATGGATGATCAAG/A (p.Ala1945_Phe1952delinsVal) and two frameshift INDELs (NC_000008.11:g.108119714CAA/C (p.Glu376fs) and NC_000008.11:g.108203577CTTATA/C (p.Ile2629fs)), which would be novel variants predicted to lead to loss of ATM functionality.

CONCLUSION

The combination of population-based biobanking and human genomics provided a novel insight of diversity of ATM gene variants at a population level. For the advancement of precision medicine, such approach will be useful to predict novel pathogenic/likely pathogenic variants in the ATM gene and to establish preventive medical guidelines for certain ATM heterozygotes pertaining to their risk of particular diseases.

Female Fabry disease patients and X-chromosome inactivation

Fabry disease is an X-linked inherited lysosomal storage disorder caused by mutations in the gene encoding α-galactosidase A (GLA). Once it was thought to affect only hemizygous males. Over the last fifteen years, research has shown that most females carrying mutated allele also develop symptoms, demonstrating a wide range of disease severity, from a virtually asymptomatic to more classical profile, with cardiac, renal, and cerebrovascular manifestations. This variable expression in females is thought to be influenced by the process of X-chromosome inactivation (XCI). The aim of this study was to assess severity of the clinical phenotype, to analyze XCI patterns, and to estimate their effect on disease manifestation in twelve female Fabry disease patients from five unrelated Polish families. Our analyses revealed that patients presented with the broad range of disease expression - from mild to severe, and their clinical involvement did not correlate with XCI profiles. Female carriers of the mutation in the GLA gene with the random XCI may present with the wide range of disease signs and symptoms. Thus, XCI is not a main factor in the phenotype variability of Fabry disease manifestation in heterozygous females.

Plasma LysoGb3: A useful biomarker for the diagnosis and treatment of Fabry disease heterozygotes

BACKGROUND

Fabry disease (FD) is a rare X-linked lysosomal storage disorder due to mutations in the α-galactosidase A gene (GLA) that result in absent or markedly reduce α-galactosidase A (α-GalA) enzymatic activity. As a result, the major glycosphingolipid substrates, globotriaosylceramide (Gb3) and globotriaosylsphingosine (LysoGb3) accumulate in plasma, urine and tissue lysosomes. In females, the diagnosis can be complicated by the fact that 40-50% of GLA-mutation confirmed heterozygotes have normal or only slightly decreased leukocyte α-GalA activities. Recently, LysoGb3 has been appreciated as a novel FD biomarker, especially for therapeutic monitoring.

METHODS

Among our GLA-mutation proven FD patients, we screened 18 heterozygotes whose leukocyte α-GalA activity was determined at initial diagnosis. For these females, we measured their serum LysoGb3 levels using highly-sensitive electrospray ionization liquid chromatography tandem mass spectrometry.

RESULTS

We identified three unrelated females in whom the accumulating LysoGb3 was increased, whereas their leukocyte α-GalA activities were in the normal range.

CONCLUSION

LysoGb3 serves as an useful biomarker to improve the diagnosis of FD heterozygotes and for therapeutic evaluation and monitoring.

Determination of optimal cutoff value to accurately identify glucose-6-phosphate dehydrogenase-deficient heterozygous female neonates

BACKGROUND

Conventional screening tests to assess G6PD deficiency use a low cutoff value of 2.10 U/gHb which may not be adequate for detecting females with heterozygous deficiency. The aim of present study was to determine an appropriate cutoff value with increased sensitivity in identifying G6PD-deficient heterozygous females.

METHODS

G6PD activity analysis was performed on 51,747 neonates using semi-quantitative fluorescent spot test. Neonates suspected with G6PD deficiency were further analyzed using quantitatively enzymatic assay and for common G6PD mutations. The cutoff values of G6PD activity were estimated using the receiver operating characteristic curve.

RESULTS

Our results demonstrated that using 2.10 U/g Hb as a cutoff, the sensitivity of the assay to detect female neonates with G6PD heterozygous deficiency was 83.3%, as compared with 97.6% using 2.55 U/g Hb as a cutoff. The high cutoff identified 21% (8/38) of the female neonates with partial G6PD deficiency which were not detected with 2.10 U/g Hb. Our study found that high cutoffs, 2.35 and 2.55 U/g Hb, would increase assay's sensitivity to identify male and female G6PD deficiency neonates, respectively.

CONCLUSIONS

We established a reliable cutoff value of G6PD activity with increased sensitivity in identifying female newborns with partial G6PD deficiency.