Ventricular septal defects (VSDs) are recognized as one of the commonest congenital heart diseases (CHD), accounting for up to 40% of all cardiac malformations, and occur as isolated CHDs as well as together with other cardiac and extracardiac congenital malformations in individual patients and families. The genetic etiology of VSD is complex and extraordinarily heterogeneous. Chromosomal abnormalities such as aneuploidy and structural variations as well as rare point mutations in various genes have been reported to be associated with this cardiac defect. This includes both well-defined syndromes with known genetic cause (e.g., DiGeorge syndrome and Holt-Oram syndrome) and so far undefined syndromic forms characterized by unspecific symptoms. Mutations in genes encoding cardiac transcription factors (e.g., NKX2-5 and GATA4) and signaling molecules (e.g., CFC1) have been most frequently found in VSD cases. Moreover, new high-resolution methods such as comparative genomic hybridization enabled the discovery of a high number of different copy number variations, leading to gain or loss of chromosomal regions often containing multiple genes, in patients with VSD. In this chapter, we will describe the broad genetic heterogeneity observed in VSD patients considering recent advances in this field.

The SALL4 gene encodes a transcription factor that is essential for early embryonic cellular differentiation of the epiblast and primitive endoderm. It is required for the development of neural tissue, kidney, heart, and limbs. Pathogenic SALL4 variants cause Duane-radial ray syndrome (Okihiro syndrome), acro-renal-ocular syndrome, and Holt-Oram syndrome. We report a family with vertical transmission of a SALL4 pathogenic variant leading to radial hypoplasia and kidney dystopia in several generations with additional growth hormone deficiency (GHD) in the proband. Our male proband was born at the 39th week of gestation. He was born small for gestational age (SGA; birth weight 2,550 g, -2.2 SDS; length 47 cm, -2.0 SDS). He had bilateral asymmetrical radial ray malformation (consisting of radial hypoplasia, ulnar flexure, and bilateral aplasia of the thumb) and pelvic kidney dystopia, but no cardiac malformations, clubfoot, ocular coloboma, or Duane anomaly. He was examined for progressive short stature at the age of 3.9 years, where his IGF-1 was 68 μg/L (-1.0 SD), and growth hormone (GH) after stimulation 6.2 μg/L. Other pituitary hormones were normal. A brain CT revealed normal morphology of the cerebral midline and the pituitary. He had a dental anomaly - a central mandibular ectopic canine. MRI could not be done due to the presence of metal after multiple corrective plastic surgeries of his hands. His mother's and father's heights are 152.3 cm (-2.4 SD) and 177.8 cm (-0.4 SD), respectively. His father has a milder malformation of the forearm. The affected paternal grandfather (height 164 cm; -2.3 SD) has a radial ray defect with missing opposition of the thumb. The family reports a similar phenotype of radial dysplasia in the paternal grandfather's mother. The proband started GH therapy at age 6.5 years when his height was 109 cm (-2.8 SDS) and he experienced catch-up growth as expected in GHD. Puberty started spontaneously at the age of 12.5 years. At age 13, his height was 158.7 cm (-0.2 SDS). Whole-exome sequencing revealed a nonsense variant in the SALL4 gene c.1717C>T (p.Arg573Ter) in the proband, his father, and paternal grandfather. This is the first observation of a patient with a congenital upper limb defect due to a pathogenic SALL4 variant who has isolated GHD with no apparent cerebral or facial midline anomaly and has been successfully treated with growth hormone.

Spalt-like 4 (SALL4) maintains vertebrate embryonic stem cell identity and is required for the development of multiple organs, including limbs. Mutations in SALL4 are associated with Okihiro syndrome, and SALL4 is also a known target of thalidomide. SALL4 protein has a distinct preference for AT-rich sequences, recognised by a pair of zinc fingers at the C-terminus. However, unlike many characterised zinc finger proteins, SALL4 shows flexible recognition with many different combinations of AT-rich sequences being targeted. SALL4 interacts with the NuRD corepressor complex which potentially mediates repression of AT-rich genes. We present a crystal structure of SALL4 C-terminal zinc fingers with an AT-rich DNA sequence, which shows that SALL4 uses small hydrophobic and polar side chains to provide flexible recognition in the major groove. Missense mutations reported in patients that lie within the C-terminal zinc fingers reduced overall binding to DNA but not the preference for AT-rich sequences. Furthermore, these mutations altered association of SALL4 with AT-rich genomic sites, providing evidence that these mutations are likely pathogenic. SALL4-related disorders include Duane-radial ray syndrome (DRRS, Okihiro syndrome), acro-renal-ocular syndrome (AROS), and SALL4-related Holt-Oram syndrome (HOS) – three phenotypes previously thought to be distinct entities. DRRS is characterized by uni- or bilateral Duane anomaly and radial ray malformation that can include thenar hypoplasia and/or hypoplasia or aplasia of the thumbs, hypoplasia or aplasia of the radii, shortening and radial deviation of the forearms, triphalangeal thumbs, and duplication of the thumb (preaxial polydactyly). AROS is characterized by radial ray malformations, renal abnormalities (mild malrotation, ectopia, horseshoe kidney, renal hypoplasia, vesicoureteral reflux, bladder diverticula), ocular coloboma, and Duane anomaly. Rarely, pathogenic variants in SALL4 may cause clinically typical HOS (i.e., radial ray malformations and cardiac malformations without additional features). The diagnosis of a SALL4-related disorder is established in a proband with suggestive findings and a heterozygous pathogenic variant in SALL4 identified by molecular genetic testing. Treatment of manifestations: Surgery as needed for strabismus from Duane anomaly, malformations of the forearms, and congenital heart defects; management of renal anomalies per nephrologist and/or urologist; antiarrhythmic medications or pacemaker for those with conduction defects or heart block; cardiologist can assist in determining the need for anticoagulants and antibiotic prophylaxis for bacterial endocarditis; hearing aids as needed; consideration of growth hormone therapy for children with growth deficiency; treatment of pituitary hypoplasia per endocrinologist. Surveillance: Ophthalmologic exam with frequency as recommended by ophthalmologist; monitor renal function in those with renal anomalies, even if renal function is normal initially; periodic renal ultrasound evaluation if renal position anomalies could cause obstruction; periodic echocardiographic surveillance may be recommended for individuals with certain congenital heart defects; in those at risk for conduction defects, EKG at least annually with consideration of annual Holter monitor in those with known conduction defects; at least annual blood counts in those with a history of thrombocytopenia and leukocytosis; audiologic evaluation as needed; assessment of growth and for signs and symptoms of pituitary hypoplasia at each visit. Agents/circumstances to avoid: Drugs affecting the kidney if renal function is impaired, or the inner ear if hearing is impaired; certain medications may be contraindicated in those with arrhythmias. SALL4-related disorders are inherited in an autosomal dominant manner. The proportion of cases caused by a de novo pathogenic variant is approximately 40%-50%. Each child of an individual with a SALL4-related disorder has a 50% chance of inheriting the pathogenic variant. Prenatal testing for a pregnancy at increased risk is possible if the pathogenic variant has been identified in an affected family member.

In the present study, clinical manifestations of two Chinese Okihiro syndrome families were analyzed, and genetic detections were performed on the two probands by exome sequencing and verified by Sanger sequencing for family members to determine the biological pathogenesis. Prenatal diagnoses were provided for three high-risk fetuses. The affected members exhibited a wildly spectrum of phenotypes, including ultrasound abnormalities of skeletal system (radius deformity and abnormal posture), and cardiac system (persistent common arterial trunk and ventricular septal defect) in the prenatal period of family 1, the severe phenotypes (grossly shortened and deformed forearm, Duane's anomaly and hearing loss), and the mild ones (usually only thenar dysplasia, or short radius styloid process). Two SALL4 variants, c.844delC p.(Q282Kfs*8) and c.2210delG p.(G737Vfs*23), have been identified respectively in two probands, and c.2210delG of SALL4 gene was unreported previously. The two variants were verified in all affected individuals, not in normal family members. Genotyping results of three fetuses indicated that one fetus was normal, and the two fetuses with heterozygous variation were affected. The two variants of SALL4 gene, c.844delC p.(Q282Kfs*8) and c.2210delG p.(G737Vfs*23), were the molecular pathological cause of Okihiro syndrome in the present study and enriched the spectrum of SALL4 variants. Our study provides accurate prenatal genetic diagnosis for the two families to avoid the birth of affected children. 本研究收集2个汉族Okihiro综合征家系患者的临床表现，应用外显子组测序对2个家系的先证者进行检测，Sanger测序对家系成员进行基因型分析，以确定生物学发病机制，并为家系中的3个高危胎儿提供产前诊断。2个家系的患者表现出广泛的表型，尤其是家系1的先证者在胎儿期就发现超声异常（桡骨畸形、姿势异常、永存动脉干和室间隔缺损等心脏畸形），其余患者表现从严重表型（前臂严重缩短和变形、杜安异常、听力障碍），到不太明显的情况（仅有大鱼际发育不良、桡骨茎突较短小）。外显子组测序在2个家系的先证者中分别发现SALL4基因变异：c.844delC p.（Q282Kfs*8）和c.2210delG p.（G737Vfs*23），其中c.2210delG p.（G737Vfs*23）为新变异。家系验证发现患者成员均携带变异，正常成员中均未检测到。同时，3个高危胎儿中共检出1例正常基因型胎儿，2例携带杂合变异胎儿并终止妊娠。本研究通过外显子组测序和Sanger测序明确了2个Okihiro综合征家系的分子病理学原因，丰富了Okihiro综合征在围产期的临床表现和SALL4基因突变图谱，同时为3个高危胎儿提供产前诊断，有效降低生育患儿的风险。.

Okihiro syndrome is an autosomal dominant condition characterized by Duane anomaly and radial ray defects. The present study aimed to analyze the clinical manifestations of a patient with Okihiro syndrome and perform genetic testing on the proband and his family to determine the biological pathogenesis. Clinical data were collected from the proband and his family and genomic DNA was extracted from peripheral blood. Whole exome sequencing was performed by high‑throughput sequencing and mutation sites of the proband and his parents were validated by Sanger sequencing. The proband was diagnosed with Okihiro syndrome, which is characterized by bone abnormality in the arms and hands (radial ray malformation, absence of thumbs) and sensorineural hearing loss. A pathogenic heterozygous c.3060delG variant was identified in exon 4 of spalt‑like transcription factor 4 (SALL4) gene in the proband. This is a frameshift mutation that changes increases the length of SALL4 protein from 1,053 to 1,076 amino acids. The variant was classed as a de novo mutation because the parents of the proband showed no variation at this site. This variant is not included in the ClinVar database and, to the best of our knowledge, has not previously been reported. The de novo heterozygous c.3060delG variant was the molecular pathological cause of Okihiro syndrome in the present study and expanded the database of known SALL4 variants.