Clinical Genetics 1979: 15: 509-512
Dizygosity of discordant twins with Noonan syndrome K. N. LAI,K. C . LAM AND J. W. M. LAWTON Departments of Medicine and Pathology, University of Hong Kong, Queen Mary Hospital, Hong Kong A pair of discordant twins, one of whom had Noonan syndrome, is reported. Most of the
cardinal signs of Noonan syndrome were demonstrated by the affected twin. The etiology of the syndrome is briefly reviewed. The dizygosity of the twins was proved by ABO blood grouping and mixed lymphocyte reaction. The findings are interpreted as reasonably good evidence that genetic factors are the prime etiology in the pathogenesis of Noonan syndrome. Received 8 November 1978, accepted f o r publication 18 January I979 Key words: Discordance; dizygosity; Noonan; twins.
The Noonan syndrome was first described as a distinct clinical entity by Noonan 6r Ehmke (1963) and Noonan (1968). Only four families in two separate studies have been reported in the literature (Baird & De Jong 1972, Collins & Turner 1973). Of the two pairs of twins so far described, the disease affected both members in one pair (Karpouzas & Papaioannou 1974), but only one in the other pair (Noonan 1968). Although the syndrome is generally assumed to be an inherited disease, the possibility of environmental teratogenic factors has never been excluded. Genetic studies on a pair of discordant twins may shed light on this problem. Materials and Method
The dizygosity of the twins was deter-
mined by ABO blood grouping and mixed lymphocyte reaction. The one-way mixed lymphocyte reaction (MLR) was performed under standardized optimal conditions cstablished in the Immunology Laboratory, Queen Mary Hospital (Hong Kong). Briefly, 5 x 104 responder cells (R) were mixed in flat-bottomed Linbro microculture tray5 with 1 x 105 mitomycin-treated stimulator cells (Sm) in a total volume of 200 p1 tissue culture medium R P M 11640, supplemented with 20 % ( V N )pooled human serum. Cultures were incubated at 37°C in 5 % COz for 6 days, after which dividing cells were pulse-labelled with 1 pCUwell 3H-thymidine (sp. act. 2 CYmmol) for 6 hours before semi-automated harvesting onto glass fiber discs using the Mini Mash harvester. 3H-thymidine incorporation was determined by scintillation counting for 10
0oO9-9163/79/060509-04$02.50/0 0 1979 Munksgaard, Copenhagen
510
LAI. L A M A N D L A W T O N
minutes. Results were expressed as incremental counts per minute per 106 cells (AcprnllOG cells). Case Report
A 17-year-old Chinese boy was admitted to Queen Mary Hospital, Hong Kong, because of abdominal pain, constipation and fever. Salmonella typhi was isolated by blood culture. The patient responded satisfactorily to chloramphenicol. Physical examination on admission revealed that his height was 135 cm and his weight 35.5 kg, both below the third percentile. He had typical features of Turner's phenotype (Fig. 1). These included hypertelorism, a relatively short neck and lowset ears. Ptosis of eyelids and antimongo-
Table 1 Results of immunological studies on the discordant twins with Noonan's syndrome Lymphocyte transformatlon (PHA & CON A) CON A 64,087 CPM1106 cells PHA 240,261 CPMI10" cells (Normal range) Mixed Lymphocyte Reaction (MLR) Patient brother's (Mit. C blocked) 121,576 CPM/10" cells cells Patient patient (Mit. C blocked) 136,851 CPM/10" cells cells pooled (Mit. C blocked) 2G9,039 CPM/lOG Patient cells allogenic cells
+
+ +
Patient's blood group 0, Rh +ve Twin brother's blood group A, Rh +ve
loid slant were prominent. H e had an undescended right testis. Auscultation revealed a grade 3/4 systolic ejectional murmur at the pulmonary area radiating down the left sternal border, P,, was diminished. Subsequent cardiac catheterization revealed valvular type of pulmonary stenosis and atrial septa1 defect. Psychological examination showed a slightly impaired intelligence: I.Q.was 75. The patient had a twin brother who was of normal height and physical appearance (Fig. 2) Clinical, radiologic, electrocardiographic and echocardiographic examination revealed no abnormality. Blood grouping and mixed lymphocyte reaction showed he was dizygotic with the patient (Table I ) There was no physical or mental abnormality in the blood relatives known t o the patient's family. Clinical, radiologic, electrocardiographic and echocardiographic examination of the five family members resident locally revealed no abnormality. Discussion
Flg. 1. Facial features of the patient with Noanan syndrome.
This patient had the clinical features of thc syndrome described by Noonan & Ehmke (1963). He and his brother are the third pair of twins affected by the syndrome so
TWINS WITH NOONAN SYNDROME
51 1
Fig. 2. The patient with his discordant twin brother.
far reported in the literature. The first pair, described by Noonan (1968), had different physical appearances and were stated to be dizygotic. The second pair, described by Karpouzas & Papaioannou (1 974), had similar physical features and were assumed to be monozygotic. Specific investigations on mono- or dizygosity of the twins were not performed. In our pair of twins, immunological studies clearly showed that they were genetically different, and therefore dizygotic.
The etiology of Noonan syndrome has not been well defined. Levy et al. (1970) first postulated that the disease might be transmitted as an autosomal dominant pattern with variable expressivity. Subsequent reports of four families revealed familial clustering. Familial clustering of a disease is generally considered to be evidence of a genetic etiology. Before accepting such presumption as fact, intrauterine infection or environmental teratogenic factors shouId be excluded. Both twins described by Karpou-
512
LAI, L A M A N D L A W T O N
zas & Papaioannou were affected by the disease. Such concordance indicated only common factors operating on both twins in utero, but did not discriminate one etiologic agent from another. The pair reported by Noonan were discordant and were stated to be dizygotic. Discordance of her twins would provide presumptive evidence for the genetic theory of the syndrome. Documentation of dizygosity in our discordant twins provides strong evidence for genetic factors being the prime etiology in the pathogenesis of Noonan syndrome. References
Baird, P. A. & B. P. De Jong (1972). Noonan syndrome (XX and XY Turner phenotype) in three generations of a family. J . Pediat. 80, 110.
Collins, E. & G. Turner (1973). The Noonan syndrome - a review of the clinical and genetic features of 27 cases. J . Pediat. 83, 941. Karpouzas, J. & A.C. Papaioannou (1974). Noonan syndrome in twins. J . Pediat. 85, 54. Levy, E. P., H. Pashayan, F. C. Fraser & L. Pinsky (1970). XX and XY Turner phenotype in a family. Amer. J . Dis. Child. 120, 36. Noonan, J. A. (1968). Hypertelorism with Turner phenotype. Amer. J . Dis. Child. 116, 373. Noonan, J. A. & D. A. Ehmke (1963). Associated noncardiac malformations in children with congenital heart diseases. J . Pediat. 63, 468. (Abst.)
Address: K . C . Lam, M.B., B.S., F.R.A.C.P. University Medical Unit Queen Mary Hospital Hong Kong
Dizygosity of discordant twins with Noonan syndrome K. N. LAI,K. C . LAM AND J. W. M. LAWTON Departments of Medicine and Pathology, University of Hong Kong, Queen Mary Hospital, Hong Kong A pair of discordant twins, one of whom had Noonan syndrome, is reported. Most of the
cardinal signs of Noonan syndrome were demonstrated by the affected twin. The etiology of the syndrome is briefly reviewed. The dizygosity of the twins was proved by ABO blood grouping and mixed lymphocyte reaction. The findings are interpreted as reasonably good evidence that genetic factors are the prime etiology in the pathogenesis of Noonan syndrome. Received 8 November 1978, accepted f o r publication 18 January I979 Key words: Discordance; dizygosity; Noonan; twins.
The Noonan syndrome was first described as a distinct clinical entity by Noonan 6r Ehmke (1963) and Noonan (1968). Only four families in two separate studies have been reported in the literature (Baird & De Jong 1972, Collins & Turner 1973). Of the two pairs of twins so far described, the disease affected both members in one pair (Karpouzas & Papaioannou 1974), but only one in the other pair (Noonan 1968). Although the syndrome is generally assumed to be an inherited disease, the possibility of environmental teratogenic factors has never been excluded. Genetic studies on a pair of discordant twins may shed light on this problem. Materials and Method
The dizygosity of the twins was deter-
mined by ABO blood grouping and mixed lymphocyte reaction. The one-way mixed lymphocyte reaction (MLR) was performed under standardized optimal conditions cstablished in the Immunology Laboratory, Queen Mary Hospital (Hong Kong). Briefly, 5 x 104 responder cells (R) were mixed in flat-bottomed Linbro microculture tray5 with 1 x 105 mitomycin-treated stimulator cells (Sm) in a total volume of 200 p1 tissue culture medium R P M 11640, supplemented with 20 % ( V N )pooled human serum. Cultures were incubated at 37°C in 5 % COz for 6 days, after which dividing cells were pulse-labelled with 1 pCUwell 3H-thymidine (sp. act. 2 CYmmol) for 6 hours before semi-automated harvesting onto glass fiber discs using the Mini Mash harvester. 3H-thymidine incorporation was determined by scintillation counting for 10
0oO9-9163/79/060509-04$02.50/0 0 1979 Munksgaard, Copenhagen
510
LAI. L A M A N D L A W T O N
minutes. Results were expressed as incremental counts per minute per 106 cells (AcprnllOG cells). Case Report
A 17-year-old Chinese boy was admitted to Queen Mary Hospital, Hong Kong, because of abdominal pain, constipation and fever. Salmonella typhi was isolated by blood culture. The patient responded satisfactorily to chloramphenicol. Physical examination on admission revealed that his height was 135 cm and his weight 35.5 kg, both below the third percentile. He had typical features of Turner's phenotype (Fig. 1). These included hypertelorism, a relatively short neck and lowset ears. Ptosis of eyelids and antimongo-
Table 1 Results of immunological studies on the discordant twins with Noonan's syndrome Lymphocyte transformatlon (PHA & CON A) CON A 64,087 CPM1106 cells PHA 240,261 CPMI10" cells (Normal range) Mixed Lymphocyte Reaction (MLR) Patient brother's (Mit. C blocked) 121,576 CPM/10" cells cells Patient patient (Mit. C blocked) 136,851 CPM/10" cells cells pooled (Mit. C blocked) 2G9,039 CPM/lOG Patient cells allogenic cells
+
+ +
Patient's blood group 0, Rh +ve Twin brother's blood group A, Rh +ve
loid slant were prominent. H e had an undescended right testis. Auscultation revealed a grade 3/4 systolic ejectional murmur at the pulmonary area radiating down the left sternal border, P,, was diminished. Subsequent cardiac catheterization revealed valvular type of pulmonary stenosis and atrial septa1 defect. Psychological examination showed a slightly impaired intelligence: I.Q.was 75. The patient had a twin brother who was of normal height and physical appearance (Fig. 2) Clinical, radiologic, electrocardiographic and echocardiographic examination revealed no abnormality. Blood grouping and mixed lymphocyte reaction showed he was dizygotic with the patient (Table I ) There was no physical or mental abnormality in the blood relatives known t o the patient's family. Clinical, radiologic, electrocardiographic and echocardiographic examination of the five family members resident locally revealed no abnormality. Discussion
Flg. 1. Facial features of the patient with Noanan syndrome.
This patient had the clinical features of thc syndrome described by Noonan & Ehmke (1963). He and his brother are the third pair of twins affected by the syndrome so
TWINS WITH NOONAN SYNDROME
51 1
Fig. 2. The patient with his discordant twin brother.
far reported in the literature. The first pair, described by Noonan (1968), had different physical appearances and were stated to be dizygotic. The second pair, described by Karpouzas & Papaioannou (1 974), had similar physical features and were assumed to be monozygotic. Specific investigations on mono- or dizygosity of the twins were not performed. In our pair of twins, immunological studies clearly showed that they were genetically different, and therefore dizygotic.
The etiology of Noonan syndrome has not been well defined. Levy et al. (1970) first postulated that the disease might be transmitted as an autosomal dominant pattern with variable expressivity. Subsequent reports of four families revealed familial clustering. Familial clustering of a disease is generally considered to be evidence of a genetic etiology. Before accepting such presumption as fact, intrauterine infection or environmental teratogenic factors shouId be excluded. Both twins described by Karpou-
512
LAI, L A M A N D L A W T O N
zas & Papaioannou were affected by the disease. Such concordance indicated only common factors operating on both twins in utero, but did not discriminate one etiologic agent from another. The pair reported by Noonan were discordant and were stated to be dizygotic. Discordance of her twins would provide presumptive evidence for the genetic theory of the syndrome. Documentation of dizygosity in our discordant twins provides strong evidence for genetic factors being the prime etiology in the pathogenesis of Noonan syndrome. References
Baird, P. A. & B. P. De Jong (1972). Noonan syndrome (XX and XY Turner phenotype) in three generations of a family. J . Pediat. 80, 110.
Collins, E. & G. Turner (1973). The Noonan syndrome - a review of the clinical and genetic features of 27 cases. J . Pediat. 83, 941. Karpouzas, J. & A.C. Papaioannou (1974). Noonan syndrome in twins. J . Pediat. 85, 54. Levy, E. P., H. Pashayan, F. C. Fraser & L. Pinsky (1970). XX and XY Turner phenotype in a family. Amer. J . Dis. Child. 120, 36. Noonan, J. A. (1968). Hypertelorism with Turner phenotype. Amer. J . Dis. Child. 116, 373. Noonan, J. A. & D. A. Ehmke (1963). Associated noncardiac malformations in children with congenital heart diseases. J . Pediat. 63, 468. (Abst.)
Address: K . C . Lam, M.B., B.S., F.R.A.C.P. University Medical Unit Queen Mary Hospital Hong Kong
