From phenotype to mechanism: Prenatal spectrum of NKAP mutation-related disorder and its pathogenesis inducing congenital heart disease.

NKAP mutations are associated with Hackmann-Di Donato-type X-linked syndromic intellectual developmental disorder (MRXSHD, MIM: #301039). Here, we elucidate the potential prenatal manifestation of NKAP mutation-associated disorder for the first time, alongside revealing the relationship between NKAP mutations and congenital heart defect (CHD) in the Chinese population. An NKAP mutation (NM_024528.4: c.988C>T, p.Arg330Cys) was identified in two foetuses presenting with CHD. Subsequent mechanistic exploration revealed a marked downregulation of NKAP transcription within HEK293T cells transfected with NKAP p.R330C. However, no significant change was observed at the protein level. Moreover, the mutation led to a dysregulation in the transcription of genes associated with cardiac morphogenesis, such as DHRS3, DNAH11 and JAG1. Additionally, our research determined that NKAP p.R330C affected Nkap protein intra-nuclear distribution, and binding with Hdac3. Summarily, our study strengthens NKAP mutations as a cause of CHD and prompts the reclassification of NKAP p.R330C as likely pathogenic, thereby establishing a prospective prenatal phenotypic spectrum that provides new insight into the prenatal diagnosis of CHD. Our findings also provide evidence of NKAP p.R330C pathogenicity and demonstrate the potential mechanism by which p.R330C dysregulates cardiac developmental gene transcription by altering Nkap intra-nuclear distribution and obstructing the interaction between Nkap and Hdac3, thereby leading to CHD.

Case report: genetic analysis of a novel frameshift mutation in FMR1 gene in a Chinese family.

Fragile X syndrome (FXS) [OMIM 300624] is a common X-linked inherited syndrome with an incidence only second to that of trisomy 21. More than 95% of fragile X syndrome is caused by reduced or absent fragile X intellectual disability protein 1 (FMRP) synthesis due to dynamic mutation expansion of the CGG triplet repeat in the 5'UTR and abnormal methylation of the FMR1 (fragile X messenger ribonucleoprotein 1) gene [OMIM 309550]. Less than 5% of cases are caused by abnormal function of the FMRP due to point mutations or deletions in the FMR1 gene. In a proband with clinical suspicion of FXS and no CGG duplication, we found the presence of c.585_586del (p.Lys195AsnfsTer8) in exon 7 of the FMR1 gene using whole exome sequencing (WES). This variant resulted in frameshift and a premature stop codon after 8 aberrant amino acids. This variant is a novel pathogenic mutation, as determined by pedigree analysis, which has not been reported in any database or literature.

[Application of chromosomal microarray analysis for fetuses with choroid plexus cysts].

OBJECTIVE: To assess the value of chromosomal microarray analysis (CMA) for fetuses with choroid plexus cysts (CPC) detected by prenatal ultrasonography. METHODS: Amniotic fluid chromosomal karyotype was analyzed in 104 fetuses with CPC, and copy number variations (CNVs) among the fetuses were detected by using CMA. RESULTS: Ten fetuses (9.62%) were found to have an abnormal karyotype, and 14 additional CNVs were detected in those with a normal karyotype. The fetuses were divided into isolated CPC group (n = 87) and non-isolated CPC group (n = 17) based on the presence of additional ultrasonographic abnormalities. The detection rates for karyotypic abnormalities of the two groups were 4.6% and 35.3%, respectively, whilst those for the CMA were 4.6% and 47.1%, respectively. The detection rates for karyotypic abnormalities and CMA of the non-isolated CPC group were significantly higher than those of the isolated CPC group (P < 0.05). The detection rate for CMA in the non-isolated group was significantly higher than chromosomal karyotype abnormalities (P < 0.05). Among the 8 fetuses with abnormal CMA, 4 had single umbilical artery, 3 had abnormal cardiac structure, and 2 had enhanced intestinal echo. CONCLUSION: CPC is closely associated with chromosomal abnormalities. Chromosome karyotype analysis in combination with CMA can effectively detect fetal chromosomal abnormalities and provide a basis for genetic counseling.

[Value of non-invasive prenatal testing for the detection of fetal chromosomal copy number variations].

OBJECTIVE: To explore the value of non-invasive prenatal testing (NIPT) for the detection of fetal chromosome copy number variations (CNVs). METHODS: Clinical data of 18 661 pregnant women who underwent NIPT were collected. For fetuses suspected for carrying CNVs, amniotic fluid samples were collected for chromosomal karyotyping and/or chromosomal microarray analysis (CMA). RESULTS: Among all samples, NIPT suggested that 58 fetuses carried trisomy 21, 18 carried trisomy 18, 19 carried trisomy 13, 1 carried trisomies 18 and 21. Eighty eight women accepted invasive prenatal diagnosis. The results of CMA in 59 cases were consistent with those of NIPT, which yielded a consistency rate of 67.05%. In addition, 37 cases of fetal CNVs were detected by NIPT, of which 19 (15 microdeletions and 4 microduplications) have accepted invasive prenatal diagnosis. In 14 cases, the results were consistency with those of NIPT, with a consistent rate of 73.68%. CONCLUSION: NIPT features high sensitivity and accuracy. Invasive prenatal diagnosis should be considered for CNVs detected by NIPT, and by tracing its parental origin, it can provide guidance for clinical practice.