Prenatal sonographic findings in confirmed cases of Wolf-Hirschhorn syndrome

Prenatal evaluation of genetic variants in fetuses with small head circumference: A single-center retrospective study

OBJECTIVES

To comprehensively evaluate the contributions of numerical chromosomal abnormality, copy number variant (CNV), and sequence variant (SV) to fetuses with small head circumference in a Chinese cohort using chromosome microarray analysis and whole exome sequencing.

METHODS

A total of 157 fetuses with small heads defined as head circumference < - 2 standard deviation (SD) were recruited between October 2014 and March 2023. We used the ultrasonic measurement parameter Z-score to define small head as possible microcephaly (3 < Z ≤ -2), microcephaly (-5 < Z ≤ -3), or pathologic microcephaly (Z ≤ -5). Ultrasound findings and genetic results were analyzed.

RESULTS

The overall diagnostic yield of chromosomal abnormalities by microarray analysis was 13 %. Whole exome sequencing revealed eight novel variants and two interesting candidate genes and provided a 25.4 % incremental yield compared with microarray analysis. Of the detected SVs, 56 % were de novo and the most common inheritance pattern was autosomal dominant inheritance presented in 11/16 fetuses. Compared with isolated small heads, non-isolated small heads had a significantly higher detection rate of chromosomal abnormalities (16 % vs. 3.0 %, P = 0.049) but not SVs (24 % vs. 5.5 %, P = 0.126). Subgroup analysis showed that intracranial anomalies had a similar high detection rate of SVs in fetuses with all small heads subgroups while no chromosomal abnormalities and causative SVs were found in fetuses with isolated possible microcephaly.

CONCLUSIONS

Ultrasound findings of small fetal head circumference < 3 SD below the mean, especially those with intracranial structural abnormalities, indicate the need for genetic counseling. Genetic variants, mainly copy number variants and SV, may be responsible for the substantial proportion of small fetal head circumference, while most are de novo. Whole exome sequencing and microarray analysis are effective diagnostic approaches for this population.

Genetic Counseling of Fetal Microcephaly

Fetal microcephaly is a small head with various losses of cerebral cortical volume. The affected cases may suffer from a wide range in severity of impaired cerebral development from slight to severe mental retardation. It can be an isolated finding or with other anomalies depending on the heterogeneous causes including genetic mutations, chromosomal abnormalities, congenital infectious diseases, maternal alcohol consumption, and metabolic disorders during pregnancy. It is often a lifelong and incurable condition. Thus, early detection of fetal microcephaly and identification of the underlying causes are important for clinical staff to provide appropriate genetic counseling to the parents and accurate management.