Abstract
The term small for gestational age (SGA) refers to infants whose birth weights and/or lengths are at least two standard deviation (SD) units less than the mean for gestational age. This condition affects approximately 3%–10% of newborns. Causes for SGA birth include environmental factors, placental factors such as abnormal uteroplacental blood flow, and inherited genetic mutations. In the past two decades, an enhanced understanding of genetics has identified several potential causes for SGA. These include mutations that affect the growth hormone (GH)/insulin-like growth factor (IGF)-1 axis, including mutations in the IGF-1 gene and acid-labile subunit (ALS) deficiency. In addition, select polymorphisms observed in patients with SGA include those involved in genes associated with obesity, type 2 diabetes, hypertension, ischemic heart disease and deletion of exon 3 growth hormone receptor (d3-GHR) polymorphism. Uniparental disomy (UPD) and imprinting effects may also underlie some of the phenotypes observed in SGA individuals. The variety of genetic mutations associated with SGA births helps explain the diversity of phenotype characteristics, such as impaired motor or mental development, present in individuals with this disorder. Predicting the effectiveness of recombinant human GH (hGH) therapy for each type of mutation remains challenging. Factors affecting response to hGH therapy include the dose and method of hGH administration as well as the age of initiation of hGH therapy. This article reviews the results of these studies and summarizes the success of hGH therapy in treating this difficult and genetically heterogenous disorder.
Highlights
The term small for gestational age (SGA) refers to infants whose birth weights and/or lengths are at least two standard deviation (SD) units less than the mean for gestational age
This paper aims to illustrate the variety of genetic mutations that are associated with SGA births while concurrently describing how other phenotype characteristics of the patient, such as motor or mental development, can vary depending on which mutation was inherited
The results showed a higher frequency of the 235Thr allele in both mothers (0.60 for SGA versus 0.36 for controls) and infants (0.59 for SGA versus 0.38 for controls) who were associated with SGA births [54]
Summary
The term small for gestational age (SGA) refers to infants whose birth weights and/or lengths are at least two standard deviation (SD) units less than the mean for gestational age. Definition and epidemiology of small for gestational age (SGA) Despite past inconsistencies in defining small for gestational age (SGA) (as reviewed by Saenger et al [1]) the International Societies of Pediatric Endocrinology and the Growth Hormone Research Society, as well as the International Small for Gestational Age Advisory Board, recently recommended that the term refer to infants whose birth weights and/or lengths are at least two standard deviation (SD) units less than the mean for gestational age [2,3]. Significant research related to genetic mutations that influence SGA has been conducted, and this article reviews the results of these studies and summarizes the success of hGH therapy in treating this condition It should be mentioned at the beginning of this review, that the number of genetic variations for any particular gene that has been associated with SGA birth does not necessarily correlate with the number of patients who have this defect. It should be noted that a second research group later sequenced IGF-1 (exons 1–6) in 53 children born SGA and determined that none of the mutations in the coding region of IGF-1 correlate with SGA stature [14]
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