Null leukemia inhibitory factor receptor (LIFR) mutations in Stuve-Wiedemann/Schwartz-Jampel type 2 syndrome

Abstract

Stuve-Wiedemann syndrome (SWS) is a severe autosomal recessive condition characterized by bowing of the long bones, with cortical thickening, flared metaphyses with coarsened trabecular pattern, camptodactyly, respiratory distress, feeding difficulties, and hyperthermic episodes responsible for early lethality. Clinical overlap with Schwartz-Jampel type 2 syndrome (SJS2) has suggested that SWS and SJS2 could be allelic disorders. Through studying a series of 19 families with SWS/SJS2, we have mapped the disease gene to chromosome 5p13.1 at locus D5S418 (Zmax=10.66 at theta =0) and have identified null mutations in the leukemia inhibitory factor receptor (LIFR or gp190 chain) gene. A total of 14 distinct mutations were identified in the 19 families. An identical frameshift insertion (653_654insT) was identified in families from the United Arab Emirates, suggesting a founder effect in that region. It is interesting that 12/14 mutations predicted premature termination of translation. Functional studies indicated that these mutations alter the stability of LIFR messenger RNA transcripts, resulting in the absence of the LIFR protein and in the impairment of the JAK/STAT3 signaling pathway in patient cells. We conclude, therefore, that SWS and SJS2 represent a single clinically and genetically homogeneous condition due to null mutations in the LIFR gene on chromosome 5p13.

Figure 1

Clinical and radiological features of patient 3. The general appearance is characterized by bowing of the lower limbs, with skin dimple and camptodactyly. X-rays of the lower limb show bowing of the long bones, with internal cortical thickening at the concave site and irregular metaphyses.

Figure 2

Map of the region encompassing the candidate genes and genomic organization of LIFR. A, The common region of homozygosity is located between markers D5S1964 and D5S1457. B, The seven candidate genes identified in that region. C and D, Exon-intron structure of the 115-kb LIFR. Mutations were identified in four extracellular domains.

Figure 3

RT-PCR detection of LIFR transcript and Scatchard analysis of high-affinity receptor. A, RT-PCR analyses were done using RNA isolated from control osteoblasts, chondrocytes, and fibroblasts and from patient fibroblasts (patients 4, 7, and 10). The specific transcript was detected in control osteoblasts, chondrocytes, and fibroblasts but was almost absent in SWS fibroblasts. B, Scatchard analysis showing specific binding of the iodinated LIF in control fibroblasts (blackened circles) and the absence of binding in patient 10 fibroblasts (unblackened circles).

Figure 4

Analysis of the STAT pathway in control and patient fibroblasts. A, Patient (patients 1, 4, and 7) and control cell lysates (C1 and C2) analyzed by western blot by use of antiphospho-Tyr STAT3 or STAT3 antibodies. Fibroblasts were stimulated with LIF (20 ng/ml) for 5 min. Only control cells gave a Phospho-STAT3 signal after LIF stimulation. B, Immunofluorescence of control and patient 10 fibroblasts with an anti-STAT3 antibody in the absence (upper panel) or presence (lower panel) of LIF (20 ng/ml) for 15 min. Only LIF-stimulated control cells showed nuclear localization of the STAT3 protein. Bar = 20μm.