Prenatal diagnosis of X-linked hydrocephalus in a family with a novel mutation in L1CAM gene

X-linked hydrocephalus genes: Their proximity to telomeres and high A + T content compared to Parkinson's disease

Proximity to telomeres (i) and high adenine and thymine (A + T) content (ii) are two factors associated with high mutation rates in human chromosomes. We have previously shown that >100 human genes when mutated to cause congenital hydrocephalus (CH) meet either factor (i) or (ii) at 91% matching, while two factors are poorly satisfied in human genes associated with familial Parkinson's disease (fPD) at 59%. Using the sets of mouse, rat, and human chromosomes, we found that 7 genes associated with CH were located on the X chromosome of mice, rats, and humans. However, genes associated with fPD were in different autosomes depending on species. While the contribution of proximity to telomeres in the autosome was comparable in CH and fPD, high A + T content played a pivotal contribution in X-linked CH (43% in all three species) than in fPD (6% in rodents or 13% in humans). Low A + T content found in fPD cases suggests that PARK family genes harbor roughly 3 times higher chances of methylations in CpG sites or epigenetic changes than X-linked genes.

Case Report: Two Novel L1CAM Mutations in Two Unrelated Chinese Families With X-Linked Hydrocephalus

L1 cell adhesion molecule is a type I transmembrane glycoprotein belonging to the immunoglobulin superfamily. Pathogenic mutations of L1CAM can cause L1 syndrome, referred to as a variety of disease spectrums characterized by hydrocephalus. In the present study, we reported two novel variants of L1CAM in two unrelated Chinese families with fetal hydrocephalus history. The woman of family 1, with three consecutive adverse birth histories of male fetuses with hydrocephalus, was identified by an exome sequence with a heterozygous mutation in the L1CAM gene, NM_000425.4: c.1696_1703 + 14del (p. S566Vfs*35), which was predicted to be pathogenic. It is predicted to disrupt RNA splicing and likely leads to an absent or disrupted protein product. In family 2, the mother, previously with once a voluntary termination of pregnancy owning to the fetus with hydrocephalus, was pregnant with a fetus with hydrocephalus in her second pregnancy. After fetal blood sampling, a pathogenic deletion of 1511bp in L1CAM, chromosome X: 153131395-153132905(hg19/GRCh37)/NM_000425.4: c.2043_2432-121del1511 leading to deletion of fibronectin type-III repeats I-II, was identified in the fetus with hydrocephalus inherited from the mother by an exome sequence. On her third pregnancy, a healthy female fetus was born without the L1CAM variant by preimplantation genetic testing for the monogenic disorder. This study emphasizes the importance of ultrasonic manifestation and family history of fetal hydrocephalus for L1CAM diagnosis. Our study expands the genotypes of L1CAM and aids the genetic counseling of fetal hydrocephalus and even preimplantation genetic testing for the monogenic disorder.

Adducted thumb may not be mandatory for prenatal diagnosis of X-linked hydrocephalus in early second trimester

OBJECTIVE

X-linked hydrocephalus (XLH), the most common genetic hydrocephalus, is caused by mutation of the L1 cell adhesion molecule (L1CAM). A fetus/neonate with this disorder frequently shows an adducted thumb, which has been employed as a helpful finding in the prenatal diagnosis of XLH.

MATERIALS AND METHODS

We describe a male fetus with hydrocephalus without an adducted thumb: the pregnancy was terminated at 21 weeks' gestation on the parents' request. Direct sequencing of the umbilical cord revealed L1CAM mutation, which confirmed the diagnosis of XLH.

RESULTS

Our literature review demonstrated that while an adducted thumb was observed in almost all fetuses with this disorder after 24 weeks' gestation, it was noted in only 57% (8/14) of fetuses/neonates at less than 24 weeks: it was absent in 43%.

CONCLUSION

Even if an adducted thumb is not observed, XLH should not be ruled out, especially in early gestation.

Prenatal diagnosis of a nonsense mutation in the L1CAM gene resulting in congenital hydrocephalus: A case report and literature review

Congenital hydrocephalus is frequently caused by mutations in the L1 cell adhesion molecule (L1CAM) gene. The purpose of the present study was to identify possible causes of fetal hydrocephalus in a Chinese family. The samples from the parents and the hydrocephalic fetus were collected. Whole-exome sequencing and in-depth mutation analysis were performed. The identified variant, c.1267C>T.(p.Q423X), is situated on exon 11 of L1CAM gene (chromosome X:153134975). The fetus was confirmed to be hemizygous for the nonsense mutation and the mother was a heterozygous carrier. The mutation turns a glutamine into a premature stop codon at amino acid position 423. In conclusion, in the present study, a nonsense mutation in the L1CAM gene was identified during the prenatal diagnosis of a congenital hydrocephalic fetus from a Chinese family. The diagnosis highlighted the necessity of genetic screening for prenatal diagnosis.

L1CAM variants cause two distinct imaging phenotypes on fetal MRI

Data on fetal MRI in L1 syndrome are scarce with relevant implications for parental counseling and surgical planning. We identified two fetal MR imaging patterns in 10 fetuses harboring L1CAM mutations: the first, observed in 9 fetuses was characterized by callosal anomalies, diencephalosynapsis, and a distinct brainstem malformation with diencephalic–mesencephalic junction dysplasia and brainstem kinking. Cerebellar vermis hypoplasia, aqueductal stenosis, obstructive hydrocephalus, and pontine hypoplasia were variably associated. The second pattern observed in one fetus was characterized by callosal dysgenesis, reduced white matter, and pontine hypoplasia. The identification of these features should alert clinicians to offer a prenatal L1CAM testing.