Anonychia and absence of distal phalanges in a patient with apparently balanced t(17;21)(q24.2;g11.2)

Abstract

Anonychia involving all 20 digits is a rare malformation which can occur alone or as part of several syndromes (Type B brachydactyly, Laband syndrome, deafnessonchodystrophy, facio-audio-synphalangism, anonychia-ectrodactyly, etc.). The distal phalanges are often absent or hypoplastic. Both autosomal dominant and autosomal recessive anonychia/onchodystrophy have been reported. None of the genes for syndromic or non-syndromic anonychia have been mapped.We report an infant with 20 digit anonychia, absence of terminal phalanges, and minor facial anomalies (mild micrognathia, small mouth, slightly beaked nose with broad nasal bridge). She was the product of a pregnancy complicated only by advanced maternal age and elevated maternal serum HCG. Amniocentesis showed her karyotype to be 46XX t(17;21)(q24.2;q11.2). This was an apparently balanced de novo translocation. Parental chromosomes were normal. Prenatal ultrasound and fetal echocardiography were interpreted as normal and the patient was born at term with a weight of 3496g, length of 47cm and OFC 35.5 cm. Examination in the newborn period showed absence of all nails and distal phalanges (confirmed on X-ray) with the above-mentioned minor facial anomalies. There were no features to suggest any of the known anonychia syndromes. Repeat karyotype confirmed the apparently balanced translocation. On follow-up at 3 months of age, her general health, growth and psychomotor development were normal.The occurrence of anonychia in a patient with an apparently balanced translocation could be due to a subtle microdeletion or duplication, altered function of a gene or genes near the breakpoints, or could be coincidental. The normal growth and development of the patient as well as the absence of previous reports of anonychia in patients with duplications or deletions involving 17q or 21q make subtle chromosomal imbalance less likely. Disruption of a gene near the breakpoint could have a dominant effect or perhaps unmask a recessive gene on the other allele. Chromosome studies in other patients with anonychia could lead to mapping of a gene for nail development.