Hypothesis: Central digit hypoplasia

Abstract

Limb deficiencies are a common birth defect. A malformations surveillance program among many newborns, stillborn fetuses, and malformed fetuses in elective terminations can identify a sufficient number of infants with the same set of abnormalities to characterize a specific limb deficiency phenotype. The active malformations surveillance program was carried out among 289,365 births at Brigham and Women's Hospital in Boston over a 41-year period (1972-2012). The research assistants identified the affected infants and fetuses from reading the findings recorded in each newborn's medical record by the examining pediatricians and consultants and by the pathologists in autopsies. One hundred ninety-four newborn infants and fetuses were found to have a limb deficiency either as an isolated abnormality or as one of multiple malformations. We identified three phenotypes of limb deficiency. We present here the seventeen infants and fetuses with "central digit hypoplasia," a term we suggest for this phenotype: hypoplasia of the thumb and fifth finger with nubbins of soft tissue in place of fingers 2, 3, and 4 at the level of the metacarpal-phalangeal joint. Central digit hypoplasia is to be distinguished primarily from the terminal transverse limb defect that ends at the wrist. In symbrachydactyly, the middle and distal phalanges of the fingers and toes are hypoplastic. In addition, central digit hypoplasia should be distinguished from the amniotic band syndrome, the most common and incorrect diagnosis suggested by the pediatricians and the consultants in this survey.The affected infant and her/his parents benefit from more accurate and specific counseling.

Hypothesis: Symbrachydactyly

“…The recognized causes among the infants of nontransferred mothers were: (1) mendelian disorders ( n = 14); (2) associated chromosome abnormalities ( n = 17); and (3) recognized syndromes ( n = 18) (Table 1). The specific phenotypes identified were: (1) amniotic band syndrome ( n = 38), based on the presence of constriction rings, crusted ends of digits, strands of tissue attached to limbs and crusted ends of one or more fingers or toes (Bamford, 1992; Moerman et al, 1992); (2) terminal transverse limb defects (TTLD) ( n = 18) ending at either the proximal forearm or at the wrist in one arm or the forefoot with residual digit‐like nubbins (Holmes & Nasri, 2022); (3) central digit hypoplasia ( n = 17), a term developed for the unilateral deformity in which there are nubbins in place of fingers 2, 3, and 4 and hypoplasia of the thumb and fifth finger (Gardiner & Holmes, 2012; Holmes & Nasri, 2022); (4) symbrachydactyly ( n = 14), the focus of this report. In addition, there were 58 infants and fetuses with either isolated or multiple limb deficiencies for whom a diagnosis was not established.…”

“…The nails may be present, hypoplastic or absent. This definition of symbrachydactyly excludes specifically: terminal transverse limb defects, the hand deformity of the Poland Anomaly, atypical split-hand (Figure 3) and the phenotype of central digit hypoplasia (Holmes & Nasri, 2022), a term suggested for the phenotype of hypoplasia of digits 1 and 5 with nubbins for fingers 2, 3, and 4 (Fig- ure 4). These four different phenotypes have been included in a broader definition of symbrachydactyly (Buck-Gramcko, 1999;Goodell et al, 2016;Imagawa, 1980;Ogino et al, 1989;Woodside & Light, 2016) (Figure 5).…”

Personal journeys to and in human genetics and dysmorphology

“…9. In developing a classification of limb deficiency, we identified three uncommon or "new" phenotypes: terminal transverse limb defects with nubbins, central digit hypoplasia, and symbrachydactyly (12). 10.…”

Surgical Reconstruction of Type IV Hypoplasia of the Thumb (Floating Thumb) in Infants: A Retrospective Analysis of Functional Outcomes and Radiographic Alignment

“…Thumb hypoplasia or absence in pediatric patients poses a complex challenge in reconstructive surgery, demanding inventive approaches to restore both form and function [1,2]. The classification of thumb hypoplasia, as proposed by previous studies, encompasses 5 distinct types: type I to type V [3,4].…”