Mutations in the SPARC-related modular calcium-binding protein 1 gene, SMOC1, cause waardenburg anophthalmia syndrome

Abstract

Waardenburg anophthalmia syndrome, also known as microphthalmia with limb anomalies, ophthalmoacromelic syndrome, and anophthalmia-syndactyly, is a rare autosomal-recessive developmental disorder that has been mapped to 10p11.23. Here we show that this disease is heterogeneous by reporting on a consanguineous family, not linked to the 10p11.23 locus, whose two affected children have a homozygous mutation in SMOC1. Knockdown experiments of the zebrafish smoc1 revealed that smoc1 is important in eye development and that it is expressed in many organs, including brain and somites.

Figure 1

Clinical and X-Ray Evaluation of the Patients (A) Image of the orbit of patient V.2. Note the short palpebral fissure, broad lateral eyebrows, and sparse eyelashes. (B) Transpalpebral ultrasonography (12 MHz) in the same child, showing the absence of eye or cystic remnants. (C) Hands of the same patient, with proximal placement of thumb, and F5 radial clinodactyly. (D) X-ray images of the hands, highlighting proximal placement of the thumb, F45 osseous syndactyly, F5 radial clinodactyly, and fusion of the capitate and hamate carpal bones. (E) Feet of the same child, showing an absent ray with sandal gap and pes planum. (F) X-rays of the feet showing, in addition, bilateral partial fusion of both the middle and the medial cuneiform bones.

Figure 2

Pedigree and Mutation Analysis (A) Pedigree showing consanguinity. (B) Electropherogram of part of SMOC1 exon 3 showing normal (1), heterozygous (2), and homozygous (3) c.378+1G>T mutation.

Figure 3

Expression of smoc1 in Zebrafish (A–D) Whole-mount in situ hybridization experiments showing early expression of smoc1 in the brain (arrow) and in the anterior retina (arrowhead) at 10 ss and 18 ss, respectively. (E and F) smoc1 is localized in the ventral retina, on both sides of the choroid fissure at 24 hr (E), and in the pharyngeal arches at 48 hpf (F). (A, C, E, and F) Top and left represent dorsal and frontal parts of the animal. (B) and (D) are top views. Magnification: 200×.

Figure 4

smoc1 Morpholino-Treated Embryos (A and C) smoc1 morpholino-injected embryos at 2 and 5 dpf, respectively. (B and D) Control morpholino-injected embryo at 2 dpf and wild-type embryo at 5 dpf. (B) RT-PCR (+ indicates with reverse transcriptase; - indicates without reverse transcriptase) on mRNA of noninjected embryos (-), embryos injected with smoc1 morpholino (MO), or those injected with control morpholino (MO-Ct) at 1 dpf. smoc1 knockdown revealed microphthalmia with defects in the ventral retina associated with abnormalities in brain development. Control for RNA extraction and amplification was performed with actin (PCR primers: 5′-GGGAG TGATG GTTGG CATGG-3′ and 5′-AGGAA GGAAG GCTGG AAGAG-3′).