Rheumatoid arthritis in an adult patient with mosaic distal 18q-, 18p- and ring chromosome 18

Introduction

Changes in the structure of chromosome 18 are implicated in a number of conditions affecting health and development. 18p- and distal 18q- syndrome has been estimated to occur in 1/50,000 and 1/40,000 live births, respectively. The characteristics of 18p- syndrome are wide ranging and include speech delay, holoprosencephaly spectrum, micrognathia, ptosis, flat nasal bridge, wide mouth with short upper lip, excessive dental caries, large protruding ears, and skeletal abnormalities. 18q- syndrome also presents with a wide variety of clinical features that commonly includes foot anomalies, carp like mouth, midface hypoplasia, cleft palate, cleft lip, inner epicanthal folds, slanted palpebral fissures, narrow or atretic external auditory canals and low set ears. Features common to both syndromes include intellectual disability, short stature, microcephaly, tone abnormalities, seizures, hearing loss and cardiac defects. The phenotypic severity of either condition appears to be correlated with the amount of genetic material affected¹.

Ring chromosome 18, or r(18), is a rarer condition that most commonly forms when there is breakage in both chromosome arms, fusion of those breakpoints and the subsequent loss of the distal fragments². Ring chromosomes can also result from terminal deletions as well as contiguous duplication, with some of these cases demonstrating inversion of these duplications and thus an inv dup del rearrangement mechanism. Individuals with a ring chromosome may have varying levels of mosaicism which is termed as “dynamic tissue mosaicism³. As a result of the inconsistent amount of duplication and hemizygosity of the distal ends, the r (18) phenotype is extremely variable. Clinical characteristics are typically a combination of 18p- and distal 18q- syndrome⁴. The occurrence of late onset lung disease in probands’ with ring chromosome 18 has not been reported. IgA deficiency and immunological diseases such as type 1 diabetes mellitus (T1DM), juvenile rheumatoid arthritis (JRA), Grave’s disease, hypothyroidism, and vitiligo have been reported in individuals with r(18)^4–9. Here we report the first case of late onset rheumatoid arthritis (RA) associated with mosaic 18p-, distal 18q-, and r(18) in a 32 year old Dominican woman with intellectual disability, hypothyroidism, vitiligo, IgA deficiency, interstitial lung disease (ILD), cystic bronchiectasis, and features consistent with both 18p- and distal 18q- syndrome.

Case report

Cytogenetics

Her primary care physician referred her to the genetics department in our hospital for suspected chromosomal abnormalities. Comparative genome hybridization (aCGH) was done using the custom designed Agilent 44,000 oligonucleotide probes microarray. Probes were placed approximately every 50–100 kb across the entire euchromatic genome with a resolution of 500 kb. The probe density at clinically relevant regions was about 5–10 kb, thus increasing the resolution to 50 kb in targeted regions based on hg19. The aCGH revealed a 14 Mb deletion at 18p11.21-p11.32 (148963-14188180)x1, a 47.8Mb duplication at 18q11.21-q22.1 (18542074-66367715)x3, and a 11.6 Mb deletion at 18q22.1-q23 (66377285-78010032)x1 (Figure 1a). Standard chromosome analysis which involved growing of lymphocytes obtained from peripheral blood in RPMI culture media supplemented with L-glutanin and Phytohemagglutanin (PHA) and antibiiotics for 72 hours, followed by mitotic arrest by adding colchicine and hypotonic treatment and fixation of cells in 3:1 methanol:acetic acid. Chromosome slides were prepared 24 hours later, and then GTG banded using Trypsin and Giemsa. Chromosome analysis was performed using the Ikaros Software (Metasystem, Germany). Of the 20 cells analyzed, 14 cells showed a ring chromosome 18 which was determined to be of chromosome 18 origin, and 4 cells showed a normal female chromosome complement. The dicentric ring was seen as a single non-clonal anomaly that was not confirmed by FISH analysis and hence omitted in the discussion of this manuscript. Fluorescence in situ hybridization Analysis (FISH) was performed to confirm the chromosome analysis findings. Briefly, slides aged for 24 hours were pretreated in 2XSSC. ThermoBrite (Vysis Inc., IL, USA) was utilized for the denaturation (73 C for 6 minutes) of the BCL2 and D18Z1 (centromere) probes followed by co-hybridization of probes to chromosomal DNA on the slides. Slides were then subjected to post-hybridization washes. Image analysis was performed using the Metasystem Ikaros Software (Metasystem, Germany). FISH analysis confirmed that 75% of the cells were ring 18 in origin with the presence of 2 BCL2 signals and one centromere 18 signal (Figure 1c). The 18 centromere signal in the picture is obscured due to its close proximity with the breakpoints close to the BCL2 DNA probe.

Figure 1.

A. CGH panel illustrates deletions on distal arms (red) and duplication of proximal long arm (blue). B. Karyotype in metaphase showing a ringed chromosome 18. C. FISH analysis showing a ringed chromosome 18.

Discussion

The described chromosomal abnormalities are most likely de novo, since maternal analysis was normal and her father was normal in appearance and health. Furthermore, ring chromosomes usually arise de novo, with only 1% inherited¹⁰. Of the inherited cases, 90% are maternal since the presence of a ring blocks spermatogenesis and induces infertility in males^12,13.

Consistent with previously reported cases of r(18) and RA (see Table 1), our patient had many of the characteristics associated with both 18p- and distal 18q- syndrome. The features shared between the two conditions include intellectual disability, short stature, microcephaly, IgA deficiency, autoimmune disorders (RA, vitiligo, hypothyroidism), and likely conductive hearing loss. Features specific to 18p- include excessive dental caries, while those specific to distal 18q- include cleft palate, carp shaped mouth, and clubfoot. Duplication did not appear to cause any distinguishing Edwards syndrome manifestations such as clenched fist, rocker bottom feet, severe organ involvement, and failure to thrive.

The unique feature of our patient was her late onset of RA compared to the early JRA previously reported^5–9,10. Our patient was RF positive, anti-CCP negative and met 9/10 of the 2010 American College of Rhematology (ACR) Clinical Classification Criteria for RA⁷. To the best of our knowledge there have been seven reported, and six published, cases of RA associated with chromosome 18 abnormalities (Table 1). Daentl first mentioned an unpublished case of JRA in a patient with 18p- and IgA deficiency⁸. In the first published case, Finley et al. reported a 9-month-old female with 18p-, swelling and contractures in many joints, fever, rash, and hepatosplenomegaly, consistent with JRA⁷. JRA has subsequently been associated with cases of 18q- as well^6,8,11.

The exact genes involved with RA and autoimmune disease development in chromosome 18 abnormalities are still not well defined. There is a suggested link between PTPN2 (protein tyrosine phosphatase non-receptor type 2), located at 18p11.2-11.3, and RA and T1DM^14,15. Genome wide studies have shown evidence for the association of the PTPN2 locus with RA susceptibility in both Japanese and European populations^14,16. A case similar to ours was reported by Jain et al. with de novo r(18), del(18q23-18qter) and del(18p11.3-18pter) associated with hyperthyroidism, T1DM, vitiligo, and IgA deficiency, but not RA⁴. Their case had a more distal deletion that likely spared PTPN2. Another autoimmune critical region was proposed on 18p, with molecular breakpoints at 12,316,423-1,231,7830; interestingly, PTPN2 is not in this region¹⁵. The genetic basis of autoimmune disease is not as well established in 18q- compared to 18p-. On the long arm, Merriman et al. proposed a locus at 18q12-21 that influences development of autoimmune diseases¹⁷. Another gene of interest is NFATc1 (nuclear factor of activated T cells) at 18q23, implicated in maintaining the programmed death receptor (PD-1) and ligand (PD-L) pathway that is essential for regulatory T cells to terminate immune responses and protect against autoimmunity^18,19. It is difficult to establish a definitive genotype-phenotype association, but it appears plausible that this proposed autoimmune critical region and PTPN2 on the short arm, as well as NFATc1 on the long arm may play a part in the autoimmune diseases seen in our patient.

Overall, adult RA has a poorer outcome compared to JRA²⁰. Mortality rates in RA patients are increased due to medication related infections, gastrointestinal bleeding as well as extra-articular pulmonary, renal disease, and cardiovascular manifestations²⁰. Our patient was also found to have ILD, bronchiectasis, and pulmonary hypertension. To the best of our knowledge, there is no known connection between interstitial lung pathologies and chromosome 18 abnormalities. However, ILD and bronchiectasis are known extra-articular manifestations of RA. In a population study, the lifetime risk of developing ILD was 7.7% for RA patients and 0.9% for non-RA subjects²¹. The classic presentation is a reticular, reticulonodular or honeycomb pattern in the lung bases.

The patient was also on several medications known to cause drug-induced interstitial lung disease (DI-ILD) including: methotrexate, adalimumab, sulfasalazine, and diclofenac²². Our report describes the first case of late onset RA associated with mosaic 18p-, 18q- and dicentric r(18). The complex rearrangements were detected by aCGH, karyotype and FISH. Her syndrome has features of both 18q- and 18p-, including multiple autoimmune disorders that support the idea of genetic loci on chromosome 18 playing a role in disease expression. Additionally, the finding of ILD - whether caused by RA, drug exposure, or an unexplored linkage - is an important condition to be aware of in patients with chromosome 18 abnormalities and autoimmune diseases.

Consent

Written and informed consent was obtained from the mother, who was the designated health care proxy prior to publishing this case report, for publication of any potentially identifiable clinical data that may be associated.