NAD+ deficiency in human congenital malformations and miscarriage: A new model of pleiotropy

Abstract

Pleiotropy is defined as the phenomenon of a single gene locus influencing two or more distinct phenotypic traits. However, nicotinamide adenine dinucleotide (NAD+) deficiency through diet alone can cause multiple or single malformations in mice. Additionally, humans with decreased NAD+ production due to changes in pathway genes display similar malformations. Here, I hypothesize NAD+ deficiency as a pleiotropic mechanism for multiple malformation conditions, including limb-body wall complex (LBWC), pentalogy of Cantrell (POC), omphalocele-exstrophy-imperforate anus-spinal defects (OEIS) complex, vertebral-anal-cardiac-tracheoesophageal fistula-renal-limb (VACTERL) association (hereafter VACTERL), oculoauriculovertebral spectrum (OAVS), Mullerian duct aplasia-renal anomalies-cervicothoracic somite dysplasia (MURCS), sirenomelia, and urorectal septum malformation (URSM) sequence, along with miscarriages and other forms of congenital malformation. The term Congenital NAD Deficiency Disorder (CNDD) could be considered for patients with these malformations; however, it is important to emphasize there have been no confirmatory experimental studies in humans to prove this hypothesis. In addition, these multiple malformation conditions should not be considered individual entities for the following reasons: First, there is no uniform consensus of clinical diagnostic criteria and all of them fail to capture cases with partial expression of the phenotype. Second, reports of individuals consistently show overlapping features with other reported conditions in this group. Finally, what is currently defined as VACTERL is what I would refer to as a default label when more striking features such as body wall defects, caudal dysgenesis, or cloacal exstrophy are not present.

Keywords: LBWC; NAD+; OEIS; VACTERL; diabetic embryopathy; discordant twins.

FIGURE 1

Features of VACTERL present in other recurrent multiple malformation conditions. LBWC, limb‐body wall complex; MURCS, Mullerian duct aplasia‐renal anomalies‐cervicothoracic somite dysplasia; OAVS, oculoauriculovertebral spectrum; OEIS, omphalocele‐exstrophy‐imperforate anus‐spinal defects; POC, pentalogy of Cantrell; URSM, urorectal septum malformation; VACTERL, vertebral‐anal‐cardiac‐tracheoesophageal fistula‐renal‐limb

FIGURE 2

The NAD+ de novo synthesis pathway and NAD+ salvage pathway. Yellow arrows depict known genes with biallelic pathogenic variants in humans. Adapted from Shi, H., Enriquez, A., Rapadas, M., Martin, E. M. M. A., Wang, R., Moreau, J., Lim, C. K., Szot, J. O., Ip, E., Hughes, J. N., Sugimoto, K., Humphreys, D. T., McInerney‐Leo, A. M., Leo, P. J., Maghzal, G. J., Halliday, J., Smith, J., Colley, A., Mark, P. R., Collins, F., Sillence, D. O., Winlaw, D. S., Ho, J. W. K., Guillemin, G. J., Brown, M. A., Kikuchi, K., Thomas, P. Q., Stocker, R., Giannoulatou, E., Chapman. G., Duncan, E. L., Sparrow, D. B., Dunwoodie, S. L. (2017). NAD deficiency, congenital malformations, and niacin supplementation. New England Journal of Medicine, 377(6), supplementary appendix, p.16. Copyright © 2017 Massachusetts Medical Society. Reprinted with permission

FIGURE 3

(a) Phenotypes of C57BL/6J wild‐type mouse embryos at E18.5, within the maternal diet treatment groups, as indicated on the left. Each horizontal bar represents a litter and length of the bars indicates the total number of embryos per litter. All dead embryos were found to be early resorptions. Total counts and percentages of embryos within each treatment group are summarized on the right. NTF, vitamin depleted and tryptophan‐free feed; TW, tryptophan‐supplemented water, 400–600 mg/L. HYP‐hypoxia at E9.5 (8% O₂, 8 h). From Cuny, H., Rapadas, M., Gereis, J., Martin, E. M. M. A., Kirk, R. B., Shi, H., Dunwoodie, S. L. (2020). NAD deficiency due to environmental factors or gene–environment interactions causes congenital malformations and miscarriage in mice. Proceedings of the National Academy of Sciences, United States of America, 117(7), 2020, supplementary appendix, p.6, figure S3. Reprinted with permission. (b) Types of NAD deficiency malformations found in mice with dietary restrictions ± hypoxia. From Cuny, H., Rapadas, M., Gereis, J., Martin, E. M. M. A., Kirk, R. B., Shi, H., Dunwoodie, S. L. (2020). NAD deficiency due to environmental factors or gene–environment interactions causes congenital malformations and miscarriage in mice. Proceedings of the National Academy of Sciences, United States of America, 117(7), p. 3741, figure 1. Reprinted with permission

FIGURE 4

Visual analogy of recurrent multiple malformation conditions discussed here, including discordant twin anomalies, demonstrating my hypothesis these are not discrete conditions, but are part of a single entity, all unified by the mechanism of NAD+ deficiency. LBWC, limb‐body wall complex; MURCS, Mullerian duct aplasia‐renal anomalies‐cervicothoracic somite dysplasia; OAVS, oculoauriculovertebral spectrum; OEIS, omphalocele‐exstrophy‐imperforate anus‐spinal defects; POC, pentalogy of Cantrell; URSM, urorectal septum malformation; VACTERL, vertebral‐anal‐cardiac‐tracheoesophageal fistula‐renal‐limb

FIGURE 5

(a) The embryonic folding process demonstrating how the embryo grows in relation to the body stalk. The diameter of the umbilical ring (gold in the image) is the same in all three embryos of Carnegie stages 9, 11, and 13. In this way, the umbilical ring decreases in size relative to the embryo. Used with permission of Elsevier Science & Technology Journals, adapted from Hartwig, N. G., Steffelaar, J. W., Van de Kaa, C., Schueler, J. A., Vermeij‐Keers, C. (1991). Abdominal wall defect associated with persistent cloaca. The embryologic clues in autopsy. American Journal of Clinical Pathology, 96(5), p. 645, figure 5. Permission conveyed through Copyright Clearance Center, Inc. (b) Demonstration on how timing of NAD+ deficiency could impact body wall formation due to closure of body wall in a cranial to caudal fashion