Agenesis, that is, failure of the kidney to develop during embryogenesis and development.

Type B1 brachydactyly (BDB1) is the most severe type of human brachydactyly, and shows high penetrance and variable expressivity. Hypoplastic or absent distal phalanges and nails of digits 2 through 5 in the hands and feet are cardinal phenotypic features of BDB1. The middle phalanges of digits 2 through 5 are usually short and may form a bony fusion with the corresponding hypoplastic distal phalanges. The deformed thumbs are often flat, broad, or bifid. A rarer feature of BDB1 is cutaneous syndactyly affecting both fingers and toes (summary by Lv et al., 2009).

Partial duplication of the distal phalanx of the thumb. Depending on the severity, the appearance on x-ray can vary from a notched phalanx (the duplicated bone is almost completely fused with the phalanx) to a partially fused appearance of the two bones.

Aplasia (absence) of the distal phalanges.

Increased width of the distal phalanx of thumb.

Coloboma is an ocular birth defect resulting from abnormal development of the eye during embryogenesis. It is defined as a congenital defect in any ocular tissue, typically presenting as absent tissue or a gap, at a site consistent with aberrant closure of the optic fissure. Failure of fusion can lead to coloboma of one or multiple regions of the inferior portion of the eye affecting any part of the globe traversed by the fissure, from the iris to the optic nerve, including the ciliary body, retina, and choroid. Coloboma is also frequently associated with small (microphthalmic) or absent (anophthalmic) eyes as part of an interrelated spectrum of developmental eye anomalies, and can affect either one or both eyes (summary by Kelberman et al., 2014). Genetic Heterogeneity of Ocular Coloboma A recessive form of ocular coloboma (216820) is caused by mutation in the SALL2 gene (602219) on chromosome 14q11.