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2011-10-01-12 Case of the week #309 © Philippe Jeanty

Answer to the case of the week #309

January 5, 2012 - January 19, 2012


Philippe Jeanty, MD

Inner Vision Women's Ultrasound, Nashville, Tennessee, USA.

Case report

This case was sent from across the world by a mother whose baby showed abnormal biometry during her prenatal ultrasound. She was afraid about the diagnosis that she had been given and was researching information about possible diagnoses. In in her effort she also sent some pictures to us. There was no known family history of skeletal dysplasias in the parent's family. Mother's body height was 160 cm; father's height was 183 cm.
Reviewing the images we suspected hypochondroplasia, since the shortening of the long bones was rather mild. The diagnosis was confirmed after birth. The baby was born at term (female, length - 45 cm, weight - 2.69 kg, head circumference - 34.5 cm).
Postnatal radiograms showed a mildly squared off pelvis; flat acetabula, proximal femoral radiolucency, and mild generalized metaphyseal changes. Although quite mild, all are consistent with a diagnosis of achondroplasia, and so FGFR3 testing was recommended by radiologist, to confirm achondroplasia or hypochondroplasia.

The FGFR3 testing result was negative for achondroplasia, but positive for hypochondroplasia, with mutation on exon 13, 1620C>A, ASN540LY, where the amnio acid asparagine is replaced by the amino acid lysine.

Hypochondroplasia is an autosomal dominant disorder characterized by short-limbed dwarfism, lumbar lordosis, short and broad bones, and caudad narrowing of the interpediculate distance of the lumbar spine. It shows some resemblance to achondroplasia, but is much milder and can be distinguished on clinical and radiographic grounds [1].

The images showed decrease biometry of the long bones (below 5%), normal biometry of the head with only slight frontal bossing, and normal skeletal ossification. No other anomalies were found. These features may give impression of mild form of achondroplasia, but the diagnosis on ultrasonographic ground is often uncertain. Biometric decrease with normal ossification, and normal cranial biometry should increase suspicion of possible hypochondroplasia, and postnatal genetic FGFR3 testing may be offered to reveal correct diagnosis.

Here are the series of images that were sent to us:
Images 1 - 11: 31+4 weeks of pregnancy:







Postnatal radiograms:





Postnatal appearance of the newborn (normal appearance)


1. Walker, B. A., Murdoch, J. L., McKusick, V. A., Langer, L. O., Jr., Beals, R. K. Hypochondroplasia. Am. J. Dis. Child. 122: 95-104, 1971.
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