Growth Standards for Children With Smith–Magenis Syndrome (SMS)

Abstract

Smith-Magenis syndrome (SMS, OMIM 182290) is a complex syndromic diagnosis marked by neurobehavioral differences and distinct facial dysmorphisms, caused by haploinsufficiency of the retinoic acid-1 (RAI1) gene either by a pathogenic sequence variant or deletion at chromosome 17p11.2 involving a portion or all of this gene. Dysmorphisms may include a broad square face and brachycephaly, heavy eyebrows, a full mouth with an everted upper lip, and early micrognathia evolving to prognathism after excessive relative mandibular growth. All patients with SMS have variable global cognitive impairment, greatest in speech/language, disturbed sleep patterns, and distinct behaviors including self-injury, food foraging, and abnormal oral intake regulation, hyperactivity, and aggression. Short stature and central obesity are common in patients with SMS, and reference curves are needed to assess growth in clinical care and research endeavors. After IRB approval, anthropometry (including length/height, weight, head circumference) was collected via direct patient encounter, parental report from external medical encounters, and extraction from medical records. Utilizing polynomial smooth splines with a B-spline basis and variable windows depending on age, sex-specific length/height and weight curves were created, including 5th, 50th and 95th percentile lines for 0 through 15 years. Head circumference data were pooled from males and females to create 5th, 50th, and 95th percentile lines for 0 through 5 years. Nearly 6000 length/height, weight, and head circumference measurements from 190 patients with SMS from birth through adulthood were gathered. Length/height and weight data were plotted against age from birth through 15 years to create new length/height-for-age and weight-for-age curves by sex. Similar processes were employed to construct head circumference-for-age curves from birth through 5 years, combining data from both sexes into one figure. Final adult height was derived from the maximum adult height for each subject over the age of 18 years. The curves included in this article represent the first set of standardized growth curves for individuals with SMS. As such, they will permit clinicians to monitor and set expectations for linear growth, weight gain, and cranial growth in individuals with SMS.