Search for ReCQL4 mutations in 39 patients genotyped for suspected Rothmund–Thomson/Baller-Gerold syndromes

Three autosomal recessive disorders have been associated with mutations in the RECQL4 gene: Rothmund–Thomson (RTS; MIM268400), Baller-Gerold (BGS; MIM218600) and RAPADILINO syndromes (MIM266280). RTS is the most prevalent phenotype in association with RECQL4 mutations, with more than 300 cases in the literature so far 1, 2. The main clinical hallmark is poikiloderma and the clinical diagnosis of RTS is currently based on the unique time of onset, and the appearance and spreading of poikiloderma. RTS diagnosis could also be discussed in cases of atypical rashes if they are associated with at least two of the following clinical signs: sparse scalp hair, eyelashes, and/or eyebrows; small size; gastrointestinal disorders; radial ray defects; radiographic bone abnormalities that include dysplasia, absent or malformed bones, osteopenia, abnormal trabeculation; dental abnormalities; dysplastic or poorly formed nails; hyperkeratosis particularly of the soles of the feet; cataracts; skin and bone cancers 2. Two clinical RTS subtypes have been defined. RTSI is characterized by poikiloderma and juvenile cataracts, and absence of RECQL4 mutations. RTSII is characterized by poikiloderma, congenital abnormalities including bone defects and an increased risk of cancer. Deleterious RECQL4 mutations are found in 2/3 of cases 1. Differential diagnoses for RTS mainly include disorders with poikiloderma [Clericuzio-type poikiloderma with neutropenia (CPN; MIM604173), Kindler syndrome (MIM173650), hereditary sclerosing poikiloderma (HSP; 173700), dyskeratosis congenita, xeroderma pigmentosum], as well as other rare genodermatoses with prominent telangiectasia but not true poikiloderma (Bloom, Werner, ataxia-telangiectasia, and Cockayne syndromes).

BGS is characterized by craniosynostosis (usually coronal), skeletal dysplasia with radial ray defects, and growth retardation 3. Differential diagnoses for BGS include disorders exhibiting radial ray hypoplasia as a major component and occasional craniosynostosis (Fanconi anaemia, foetal valproate syndrome, VACTERL, SALL4-related disorders, Holt–Oram syndrome, thrombocytopenia-absent radius syndrome) and syndromes with predominant craniosynostosis, in particular Saethre–Chotzen syndrome (SCS, MIM101400; 4 5). RECQL4 mutations have only been found in a subset of patients with BGS and poikiloderma 3.

Because only a few genes have been assigned to syndromic poikiloderma or BGS, the search for RECQL4 mutations is often prescribed, given the risks of recurrence and of malignancy. From the 5-year experience of a laboratory offering RECQL4 screening as a diagnostic test, we analysed a cohort of 39 patients referred for RECQL4 screening in order to determine the best indicators for RECQL4 sequencing, as well as possible diagnosis in negative patients.

Patients and methods

Results

Clinical analysis

In cohort 1, the patients were analysed depending on whether or not they carried RECQL4 mutations. Detailed clinical data in the 10 patients with RECQL4 mutations are presented in Table 1 (Fig. 1). Besides poikiloderma, all patients had other manifestations of the RTSII spectrum (growth retardation, skeletal manifestations and/or digestive abnormalities), except the patient with only one RECQL4 mutation with a phenotype limited to skin appendages.

Clinical and molecular reevaluation of RECQL4-negative patients led to a diagnosis of HSP in five patients in the presence of tendon contractures and myopathy, CPN in one patient, and CDAGS (craniosynostosis, anal anomalies, and porokeratosis) in one patient in the presence of suspected poikiloderma, alopecia and bone manifestations including craniosynostosis and a sibling presenting with porokeratosis and anal atresia (Fig. 2). Four of the five patients with HSP were molecularly confirmed in the context of the recent identification of the causal gene 7. Among the 10 remaining RECQL4-negative cases, a diagnosis of RTS could not be ruled out despite negative RECQL4 sequencing in one case in the presence of growth retardation and skeletal abnormalities, whereas the others could be classified into two groups: (i) syndromic poikiloderma with developmental delay (n = 5); (ii) isolated poikiloderma when no involvement of organs other than skin appendages (n = 4; Fig. 2). Within the group with syndromic poikiloderma, one patient had juvenile cataract, but it was difficult to raise the diagnosis of RTSI in the presence of developmental delay. Within the group with abnormalities limited to skin appendages, a new entity was probable in a consanguineous family with recurrence in siblings, with total alopecia, normal stature and multiple spinocellular-type skin cancer.

The clinical features of patients of cohort 2 are presented in Table 2.

Table 2. Clinical data of the 12 patients referred for BGS diagnosis in our series

	BGS patient with one TWIST mutation	BGS patient with abnormal array-CGH	Other BGS patients(n = 10)
Sex (male/female)	0/1	0/1	6/4
Familial history	+	−	0/10
Consanguinity	−	−	3/10
Mean age at referral (years)	26	8	7 [2.0–21.7]
Facial dysmorphism	+	+	10/10
Craniosynostosis	+	+	8/10
Type of craniosynostosis
Coronal	+	NA	3/7
Other	NA	NA	3/7
Radial ray malformations
Thumb agenesis/hypoplasia	+	NA	8/9
Other radial ray defects	−	+	7/9
Other skeletal abnormalities
Patellar hypoplasia	−	NA	1/3
Joint luxations	−	NA	2/7
Others	Carpus, metatarsus and phalange abnormalities	Scoliosis	8/9a
Growth retardation	−	NA	4/8
Skin abnormalities	−	−	0/10
Intellectual deficiency	−	+	3/7
Visceral malformations			b
Digestive malformations	Oesophageal atresia	−	2/8
Cardiac malformations	−	−	4/8
Genital malformations	−	−	1/7
Renal malformations	−	−	4/8
Cerebral malformations	NA	NA	2/8
Eye abnormalities	Ptosis	−	3/8
Others
Cleft palate	+	−	1/8

• NA, not available.
• ^a Including five cases with short hands and feet, four cases with joint contractions, four cases with cubital abnormalities, three cases with vertebral abnormalities, and three cases with carpal, tarsal and phalangeal abnormalities.
• ^b Including anal anteposition (n = 1), oesophageal atresia (n = 1), atrial septal defect (n = 2), ventricular septal defect (n = 1), tetralogy of Fallot (n = 1), complex heart malformation (n = 1), hypospadias (n = 1), renal agenesis (n = 1), hypoplastic kidney (n = 1), kidney ectopia (n = 2), holoprosencephaly (n = 1), thin corpus callosum (n = 1), strabismus (n = 2) and cataract (n = 1).

Discussion

From our series of 39 patients with suspected RTS and BGS referred for RECQL4 screening, we aimed to define the best indicators for RECQL4 sequencing and to search for differential diagnoses in negative patients, in order to help physicians faced with such diagnoses in clinical practice.

We first confirmed that RECQL4 sequencing was not justified in BGS patients without poikiloderma. In order to avoid confusion, the presence of BGS features with poikiloderma would rather be considered a severe presentation of RTS, especially because poikiloderma was not mentioned in the initial definition of BGS 8. We showed that the prescription of array-CGH and TWIST1 sequencing led to higher diagnostic work-up than RECQL4 screening in patients with suspected BGS without poikiloderma 8. Interestingly, another patient with craniosynostosis, abnormal corpus callosum, intellectual deficiency and a 11.2 Mb deletion at the same locus (ch1:58927412–70127412;hg19), has been reported in the Decipher database, suggesting that this locus can be candidate for syndromic craniosynostosis.

Within cohort 1, 25/27 patients met the criteria for possible RTS as defined by Wang and Plon 2 even though only 10 had at least one RECQL4 mutation. These criteria were therefore not appropriate to differentiate positive from negative RECQL4 patients. All of the patients with two RECQL4 mutations had at least one of the three features including growth retardation, skeletal manifestations and digestive abnormalities, and absence of developmental delay.

The search for alternative diagnoses in patients with absence of RECQL4 mutations was a useful strategy. Because CPN could be a differential diagnosis in the presence of poikiloderma, the C16orf57/USB1 gene was screened, leading to CPN diagnosis in one patient with previously undetected neutropenia 6. Because it is now shown that all patients with C16orf57/USB1 mutations have neutropenia, the search for neutropenia should be mandatory in patients with poikiloderma 6. In addition, five patients had features in favour of HSP, in particular tendon contractures and myopathy. HSP has recently been described in a South African family with congenital poikiloderma, hypotrichosis, hypohidrosis, tendon contractures with varus feet, and the causal gene was recently identified as FAM111B 7, 9. In a few cases, the diagnosis of poikiloderma can also be difficult. For example, one patient with suspected poikiloderma was reassigned to CDAGS syndrome after the birth of a sibling, presenting with porokeratosis and anal atresia 10. From this experience, given the high number of genodermatoses presenting with poikiloderma, this pattern of presentation should be considered carefully, with special attention paid to features in favour of CPN or HSP.

In the literature, it is mentioned that RECQL4 mutations could be detected in 60–65% of affected individuals with RTS, suggesting genetic heterogeneity 1. From the retrospective reevaluation, the percentage of convincing negative RTS cases appeared lower in our series (1/10 cases with no RECQL4 mutation, Fig. 2). In the remaining patients, because of partial clinical overlap, ambiguity can be resolved by RECQL4 sequencing until additional progress has been made in the clinical delineation and molecular basis of other syndromes with poikiloderma.

In conclusion, we showed that a significant number of patients reported in the past as RTS with poikiloderma might carry other entities that would benefit from clinical dissection with the help of next generation sequencing tools. This study should lead to a reduction in the prescription of RECQL4 sequencing analysis, but molecular testing remains necessary in cases with overlapping features and undefined diagnosis to ensure appropriate genetic counselling and specific oncosurveillance.