A Novel Frameshift CHD4 Variant Leading to Sifrim-Hitz-Weiss Syndrome in a Proband with a Subclinical Familial t(17;19) and a Large dup(2)(q14.3q21.1)

The genetic complexity of neurodevelopmental disorders (NDD), combined with a heterogeneous clinical presentation, makes accurate assessment of their molecular bases and pathogenic mechanisms challenging. Our purpose is to reveal the pathogenic variant underlying a complex NDD through identification of the "full" spectrum of structural genomic and genetic variants. Therefore, clinical phenotyping and identification of variants by genome and exome sequencing, together with comprehensive assessment of these and affected candidate genes, were carried out. A maternally-inherited familial translocation [t(17;19)(p13.1;p13.3)mat] disrupting the GSG1 like 2 gene (GSG1L2), a 3.2 Mb dup(2)(q14.3q21.1) encompassing the autosomal dominant OMIM phenotype-associated PROC and HS6ST1 gene, and a novel frameshift c.4442del, p.(Gly1481Valfs*21) variant within exon 30 of the Chromodomain helicase DNA binding protein 4 (CHD4) have been identified. Considering the pathogenic potential of each variant and the proband's phenotype, we conclude that this case basically fits the Sifrim-Hitz-Weiss syndrome or CHD4-associated neurodevelopmental phenotype. Finally, our data highlight the need for identification of the "full" spectrum of structural genomic and genetic variants and of reverse comparative phenotyping, including unrelated patients with variants in same genes, for improved genomic healthcare of patients with NDD.

Prenatal diagnosis and ultrasonographic findings of partial trisomy of chromosome 6q: A case report and review of the literature

RATIONALE

Partial trisomy of the long arm of chromosome 6 syndrome is a rare chromosomal disorder with distinctive phenotypic expressivity, in which cytogenetic abnormalities are usually reported in infancy and childhood. Ultrasonographic findings on trisomy of the distal long arm of chromosome 6 in previous studies are limited.

PATIENT CONCERNS

A 32-year-old, gravida 6, para 1, pregnant woman who had 4 spontaneous abortions underwent a clinical ultrasound examination at 26 weeks of gestation.

DIAGNOSES

Ultrasonographic findings were microcephaly, an acoustic image of a transparent septum, a flat nasal bridge, right pulmonary artery stenosis, and a single umbilical artery. Cytogenetic and single-nucleotide polymorphism array analyses were performed to estimate genetic factors of this diagnosis by amniocentesis.

INTERVENTIONS

After genetic counseling, the patient and her husband opted to terminate the pregnancy.

OUTCOMES

Cytogenetic examination of the fetus showed the karyotype 46,XX,der(20)t(6;20)(q24;p13). The single-nucleotide polymorphism (SNP) array showed a 22.104-Mb duplication of 6q24.3q27 and a 0.784-Mb deletion of 20p13.

LESSONS

Ultrasonographic findings of fetal abnormalities, including microcephaly, an acoustic image of a transparent septum, a flat nasal bridge, right pulmonary artery stenosis, and a single umbilical artery, may be related to a 22.104-Mb duplication of 6q24.3q27 and a 0.784-Mb deletion of 20p13. More ultrasonographic and genotype studies are required to extend the phenotypic characterization of partial trisomy 6q syndrome.

Clinical diagnosis of neurofibromatosis type I in multiple family members due to cosegregation of a unique balanced translocation with disruption of the NF1 locus: Testing considerations for accurate diagnosis

Neurofibromatosis type 1 (NF1) is an autosomal dominant disorder that causes a predisposition to develop tumors along the peripheral nervous system. The NF1 gene, located at 17q11.2, has the highest mutation rate among known human genes and about half of NF1 patients have de novo pathogenic variants. We present a case of clinical NF1 diagnoses in multiple family members with phenotypes ranging from mild to severe. Chromosome analysis of the 3-year-old female proband with NF1 resulted in an abnormal karyotype that was inherited from her mother: 46,XX,t(4;17)(q21.3;q11.2) mat. However, no NF1 genetic variants were identified by either NGS analysis of NF1 DNA coding regions, deletion-duplication studies, or by cytogenomic microarray copy number analysis. Follow-up chromosome studies of the proband's two male siblings demonstrated cosegregation of the same balanced translocation and a clinical diagnosis of NF1. Based on the cosegregation of the translocation with the NF1 clinical presentation in this family, we hypothesized that the NF1 gene may have been disrupted by this unique rearrangement. Subsequent fluorescence in situ hybridization (FISH) analysis of the metaphase cells of an affected sibling revealed a disruption of the NF1 gene confirming the underlying basis of the clinical NF1 presentation in this family. The utilization of traditional cytogenetic as well as evolving molecular methods was not only pivotal in the diagnosis of NF1 and management for this family, but is also pertinent to other patients with a family history of NF1.