Clinical Description
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 [Al-Baradie et al 2002, Kohlhase et al 2002, Kohlhase et al 2003, Borozdin et al 2004a, Borozdin et al 2004b, Kohlhase et al 2005, Borozdin et al 2007].
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).
Of 69 affected individuals from 23 families with a SALL4 pathogenic variant, 13% show the triad of Duane anomaly, radial ray malformation, and sensorineural hearing loss originally described for Okihiro syndrome; 45% have Duane anomaly and radial defects; and 21% have radial defects only. To date, more than 100 individuals with a pathogenic variant in SALL4 have been identified [Al-Baradie et al 2002, Kohlhase et al 2002, Kohlhase et al 2003, Borozdin et al 2004a, Borozdin et al 2004b, Kohlhase et al 2005, Borozdin et al 2007, Vanlerberghe et al 2019, van de Putte et al 2020, and others]. The following description of the phenotypic features associated with this condition is based on these reports.
Ocular. Duane anomaly is the most common ocular finding. Other ocular anomalies include iris, retinal, and choroidal colobomata, cataract, optic disc hypoplasia, and microphthalmia (structural eye anomalies are rare).
Musculoskeletal. Radial ray anomalies 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). Other reported upper-extremity anomalies include concomitant shortening of ulnae, syndactyly, radial clubhand, carpal bone anomalies, shortened humeri, and hypoplasia of deltoid muscles. Lower-extremity anomalies include talipes, clubfoot, tibial hemimelia, and syndactyly of toes. Fused vertebrae have also been reported.
Renal anomalies include mild malrotation, ectopia, crossed renal ectopia, horseshoe kidney, renal hypoplasia, renal agenesis, vesicoureteral reflux, and bladder diverticula.
Cardiac. Congenital heart malformations include ventricular septal defect, atrial septal defect, and tetralogy of Fallot. Cardiac conduction defects are also reported but are less common than in TBX5-related HOS.
Ears/hearing. Sensorineural and/or conductive deafness can occur. Ear anomalies include abnormal pinnae, slit-like opening of auditory canals, and small ears.
Gastrointestinal features can include anal stenosis and imperforate anus.
Characteristic facial features reported in some individuals include epicanthal folds, widely spaced eyes, depressed nasal bridge, and hemifacial microsomia.
Pituitary. Growth hormone deficiency, postnatal growth deficiency, pituitary hypoplasia
Development and cognition are normal.
Other
Genotype-Phenotype Correlations
Most SALL4 loss-of-function variants are private or have been observed in no more than three independent families. The phenotype of larger deletions (not extending into other genes) is not significantly different from that caused by almost all truncating single-nucleotide variants, and these are expected to result in nonsense-mediated mRNA decay.
The only clearly pathogenic missense variant identified to date in an individual with malformations (c.2663A>G, p.His888Arg) affects an essential coordinating amino acid and is associated with central midline defects (single upper incisor, pituitary hypoplasia, widely spaced eyes). It is predicted to result in an increase of DNA binding capacity [Miertus et al 2006].
The only truncating pathogenic variant predicted to escape nonsense-mediated mRNA decay is associated with extensive clinical variability and severe hemifacial microsomia in one affected member of the reported family [Terhal et al 2006].
Some pathogenic missense variants have been reported to result in a gain of function, and those variants have been reported to cause premature ovarian failure alone, without developmental disorder (see Genetically Related Disorders) [Wang et al 2019].
Penetrance
Penetrance is approximately 95% but may be lower for certain pathogenic variants.
In two reported families. An individual known (on the basis of pedigree position) to have the SALL4 pathogenic variant is unaffected; an individual with a proven SALL4 pathogenic variant shows no signs of a SALL4-related disorder [Hayes et al 1985, Kohlhase et al 2002]. In the latter family, however, the phenotype was mild in all individuals with the pathogenic variant (i.e., presenting with only thenar hypoplasia and Duane anomaly).
Of 69 family members known in 2004 to have a SALL4 pathogenic variant, only one (1.4%) was clinically unaffected [J Kohlhase, personal observation]. No further case of non-penetrance is known to the author.
Nomenclature
One of the earliest reports of Duane anomaly occurring together with radial ray defects is that of Ferrell et al [1966] (earlier reports are cited in OMIM). Further families were reported by Temtamy et al [1975] and Okihiro et al [1977]. Temtamy & McKusick [1978] named the syndrome Duane/radial dysplasia syndrome (DR syndrome, later modified to Duane-radial ray syndrome [DRRS]). The term "Okihiro syndrome" was first used by Hayes et al [1985].
The term "acro-renal-ocular syndrome" was used in 1984 to describe a family with autosomal dominant inheritance of thumb abnormalities, renal malformations, and ocular coloboma, ptosis, and Duane anomaly [Halal et al 1984].
Holt-Oram syndrome has also been referred to as heart-hand syndrome, a nonspecific designation that could apply to any number of conditions with involvement of these structures.