Birth Weight and Length May Help Identify Newborns with Prader-Willi Syndrome

Newborns with Prader-Willi syndrome often have a lower birth weight and can be shorter than newborns who do not have this rare disease, a study conducted in Italy reports.

Recognition of these body features may help clinicians in diagnosing the syndrome earlier, and in beginning suitable support and treatment measures for long-term care.

The study, “Antropometric characteristics of newborns with Prader-Willi syndrome,” was published in the American Journal of Medical Genetics.

A sequence of clinical events are common to people with Prader-Willi syndrome (PWS) and help in diagnosing the disease beginning in early infancy. It starts by unexplained general low muscle tone and a poor ability to suck, often followed by excessive weight gain that can lead to early obesity.

Other common features include hormone imbalances, musculoskeletal issues, cognitive disability, and short stature. In fact, short stature is another physical characteristic of Prader-Willi syndrome, whose patients have a poor growth velocity during childhood and lack the growth spurt of puberty.

Difficult to detect fetal movements are commonly reported during gestation, with an increased incidence of preterm births. The stature of newborns is generally within the normal range, while full-term birth weight of PWS infants is typically 15% to 20% lower than that of other newborns.

Italian researchers explored the distribution of weight and length at birth of 252 males and 244 females with Prader-Willi syndrome born in the country between 1988 and 2018. All were born to parents of Italian origin at between 36 and 42 gestational weeks (a birth is considered full-term at 39 gestational weeks).

Their aim was to produce standardized growth curves for these newborns, to help with diagnosing Prader-Willi and following its progression. For example, a low birth weight is considered to be a risk factor for metabolic and cardiovascular ills.

Prader-Willi syndrome can be due to multiple genetic defects, and 341 of the newborns had undergone genetic testing. In 142 of these children, a region of the paternal copy of chromosome 15 (known as the 15q11.2-13 region) was deleted, preventing  production of the encoded genes; 127 had a genetic abnormality called maternal uniparental disomy (mUPD15), where two copies of chromosome 15 are inherited from the mother and none from the father; four had other genetic defects; and the final 68 children had an unidentified genetic defect.

Compared to healthy newborns, those with Prader-Willi were approximately 0.5 kg (1.1 pounds) lighter, and were 1 cm (0.4 inches) shorter. Previous studies identified similar trends in different ethnic groups. The head circumference of PWS newborns was similar to that of healthy babies.

Statistical analysis of the distribution of birth weight and length, taking into consideration the gestational age, showed that males with a paternal chromosome 15 deletion had similar weight and length patterns to males with mUPD15. However, the same statistical analysis for females showed that those with the paternal chromosome 15 deletion were shorter than those with mUPD15.

Overall, “the present growth curves may be useful as further traits in supporting a suspicion of PWS [Prader-Willi syndrome] in a newborn,” the researchers wrote.

“Because impaired prenatal growth increases risk of health problems later in life, having neonatal anthropometric standards could be helpful to evaluate possible correlations between the presence or absence of small gestational age and some clinical and metabolic aspects of PWS,” they concluded.