[Clinical features and genetic testing of a Chinese pedigree affected with Smith-Lemli-Opitz syndrome].

OBJECTIVE

To analyze the clinical features and genetic variants of two patients from a pedigree affected with Smith-Lemli-Opitz syndrome and explore their genotype-phenotype correlation.

METHODS

Clinical data and family history of the pedigree were collected. Whole exome sequencing was carried out to identify the potential variants. Suspected variants were verified by Sanger sequencing of the family members.

RESULTS

The proband and her sister both presented with feeding difficulty, facial dysmorphism, seizures, and mental and speech retardation. The third child of this family presented with feeding difficulty, poor weight gain and severe malnutrition after birth. He had died of unknown cause at 6 months without genetic testing. The fourth child was a healthy boy. Genetic testing showed that both the proband and her sister have carried c.127G>T (p.Val43Phe) and c.820_825del (p.Asn274_Val275del) compound heterozygous variants of the DHCR7 gene (NM_001360.2), but the fourth child carried neither of the variants. The two variants were unreported in the literature and disease-related databases, and were not included in the 1000G and gnomAD databases. The c.820_825del variant may affect the sterol-sensitive region of the DHCR7 protein, which can lead to deletion of two amino acids at positions 247 and 275, causing truncation of the DHCR7 protein. It is speculated that this may affect the stability of protein's spatial conformation, thereby decrease the activity of the enzyme. The c.127G>T variant may affect the first transmembrane region of the protein, which is involved in the transmembrane transport of proteins. Multiple software predicted it to be harmful. Conservation analysis suggested that the three amino acids all locate in a highly conserved region of the protein. In consideration of the clinical phenotype, family history and result of genetic testing, we speculated that both patients had Smith-Lemli-Opitz syndrome due to variants of the DHCR7 gene.

CONCLUSION

This pedigree has enriched the phenotypic and genotypic data of Smith-Lemli-Opitz syndrome, which clarified the genetic etiology of the patients and provided a basis for genetic counseling of this pedigree.