Relevance of Extending FGFR3 Gene Analysis in Osteochondrodysplasia to Non-Coding Sequences: A Case Report

Skeletal dysplasia, also called osteochondrodysplasia, is a category of disorders affecting bone development and children's growth. Up to 552 genes, including fibroblast growth factor receptor 3 (FGFR3), have been implicated by pathogenic variations in its genesis. Frequently identified causal mutations in osteochondrodysplasia arise in the coding sequences of the FGFR3 gene: c.1138G>A and c.1138G>C in achondroplasia and c.1620C>A and c.1620C>G in hypochondroplasia. However, in some cases, the diagnostic investigations undertaken thus far have failed to identify the causal anomaly, which strengthens the relevance of the diagnostic strategies being further refined. We observed a Caucasian adult with clinical and radiographic features of achondroplasia, with no common pathogenic variant. Exome sequencing detected an FGFR3(NM_000142.4):c.1075+95C>G heterozygous intronic variation. In vitro studies showed that this variant results in the aberrant exonization of a 90-nucleotide 5' segment of intron 8, resulting in the substitution of the alanine (Ala359) for a glycine (Gly) and the in-frame insertion of 30 amino acids. This change may alter FGFR3's function. Our report provides the first clinical description of an adult carrying this variant, which completes the phenotype description previously provided in children and confirms the recurrence, the autosomal-dominant pathogenicity, and the diagnostic relevance of this FGFR3 intronic variant. We support its inclusion in routinely used diagnostic tests for osteochondrodysplasia. This may increase the detection rate of causal variants and therefore could have a positive impact on patient management. Finally, FGFR3 alteration via non-coding sequence exonization should be considered a recurrent disease mechanism to be taken into account for new drug design and clinical trial strategies.

Clinical heterogeneity of NADSYN1-associated VCRL syndrome

The NADSYN1 gene [MIM*608285] encodes the NAD synthetase 1 enzyme involved in the final step of NAD biosynthesis, crucial for cell metabolism and organ embryogenesis. Perturbating the role of NAD biosynthesis results in the association of vertebral, cardiac, renal, and limb anomalies (VCRL). This condition was initially characterized as severe with perinatal lethality or developmental delay and complex malformations in alive cases. Sixteen NADSYN1-associated patients have been published so far. This study illustrates the wide phenotypic variability in NADSYN1-associated NAD deficiency disorder. We report the clinical and molecular findings in three novel cases, two of them being siblings with the same homozygous variant and presenting with either a very severe prenatal lethal or a mild phenotypic form. In addition to an exhaustive literature, we validate the expansion of the spectrum of NAD deficiency disorder. Our findings indicate that NAD deficiency disorder should be suspected not only in the presence of the full spectrum of VCRL, but even a single of the aforementioned organs is affected. Decreased plasmatic levels of NAD should then strongly encourage the screening for any of the genes responsible for a NAD deficiency disorder.

Risk estimation of uniparental disomy of chromosome 14 or 15 in a fetus with a parent carrying a non-homologous Robertsonian translocation. Should we still perform prenatal diagnosis?

OBJECTIVE

Uniparental disomy (UPD) testing is currently recommended during pregnancy in fetuses carrying a balanced Robertsonian translocation (ROB) involving chromosome 14 or 15, both chromosomes containing imprinted genes. The overall risk that such a fetus presents a UPD has been previously estimated to be around ~0.6-0.8%. However, because UPD are rare events and this estimate has been calculated from a number of studies of limited size, we have reevaluated the risk of UPD in fetuses for whom one of the parents was known to carry a nonhomologous ROB (NHROB).

METHOD

We focused our multicentric study on NHROB involving chromosome 14 and/or 15. A total of 1747 UPD testing were performed in fetuses during pregnancy for the presence of UPD(14) and/or UPD(15).

RESULT

All fetuses were negative except one with a UPD(14) associated with a maternally inherited rob(13;14).

CONCLUSION

Considering these data, the risk of UPD following prenatal diagnosis of an inherited ROB involving chromosome 14 and/or 15 could be estimated to be around 0.06%, far less than the previous estimation. Importantly, the risk of miscarriage following an invasive prenatal sampling is higher than the risk of UPD. Therefore, we do not recommend prenatal testing for UPD for these pregnancies and parents should be reassured.